Microsoft Word - CPG18 Care of the Patient with Accommodative Vergence.doc

Accommodative and Vergence Dyxfunction iii

TABLE OF CONTENTS

INTRODUCTION

............................................................................................. 1

STATEMENT OF THE PROBLEM

................................................. 3

Description and Classification of Accommodative and Vergence
Dysfunction .................................................................................. 4

Accommodative

Dysfunction ............................................. 5

Accommodative

Insufficiency .................................. 5

Ill-Sustained Accommodation................................... 5

Accommodative Infacility......................................... 5

Paralysis

Accommodation .................................... 6

Spasm

Accommodation ........................................ 6

Vergence

Dysfunction ........................................................ 6

Convergence

Insufficiency........................................ 8

Divergence

Excess .................................................... 8

Basic

Exophoria ........................................................ 9

Convergence

Excess ................................................. 9

Divergence

Insufficiency .......................................... 9

Basic Esophoria ........................................................ 9

Fusional

Vergence

Dysfunction ................................ 9

Vertical

Phorias......................................................... 9

Epidemiology of Accommodative and Vergence Dysfunction .. 10

Accommodative

Dysfunction ........................................... 10

Prevalence ............................................................... 10

Risk

Factors ............................................................ 10

Vergence

Dysfunction ...................................................... 11

Prevalence ............................................................... 11

Risk Factors ........................................................... 12

Clinical Background of Accommodative and Vergence

Dysfunction............................................................................... 13

Accommodative

Dysfunction ........................................... 13

Natural History........................................................ 13

Common Signs, Symptoms, and Complications ..... 14

Early

Detection and Prevention .............................. 15

Vergence

Dysfunction ...................................................... 16

Natural History........................................................ 16

Common Signs, Symptoms, and Complications ..... 19

Early

Detection and Prevention .............................. 23

iv Accommodative and Vergence Dyxfunction

II.

CARE

PROCESS

.............................................................................. 25

Diagnosis

Accommodative and Vergence Dysfunction......... 25

Patient

History .................................................................. 25

Ocular

Examination.......................................................... 26

Visual

Acuity.................................................................... 27

Refraction................................................................ 27

Ocular

Motility and Alignment............................... 28

Near

Point

Convergence ..................................... 28

Near

Fusional

Vergence

Amplitudes ...................... 29

Relative

Accommodation

Measurements................ 30

Accommodative

Amplitude and Facility ................ 30

Stereopsis ................................................................ 30

Ocular Health Assessment and Systemic Health
Screening................................................................. 31

Supplemental

Tests........................................................... 31

Accommodative

Convergence/Accommodation

Ratio........................................................................ 31

Fixation

Disparity/Associated Phoria...................... 33

Distance

Fusional

Vergence

Amplitudes ................ 33

Vergence

Facility .................................................... 33

Accommodative

Lag ............................................... 33

Assessment

and Diagnosis................................................ 34

Graphical

Analysis.................................................. 34

Zones

Comfort .................................................... 35

Comparison

to Expected Values ............................. 35

Fixation Disparity and Vergence Adaptation.......... 37

Comparison

Methods of Analysis....................... 37

Management of Accommodative and Vergence Dysfunction .... 38

Basis for Treatment .......................................................... 38

Vision

Therapy........................................................ 38

Lens and Prism Therapy ......................................... 46

Available

Treatment

Options............................................ 49

Optical Correction................................................... 49

Vision

Therapy........................................................ 51

Medical

(Pharmaceutical)

Treatment ...................... 52

Surgery.................................................................... 53

Management Strategy for Accommodative Dysfunction.. 53

Accommodative

Insufficiency ................................ 53

Ill-Sustained

Accommodation................................. 53

Accommodative Infacility....................................... 53

Paralysis

Accommodation .................................. 53

Spasm

Accommodation ...................................... 54

Accommodative and Vergence Dyxfunction v

Management Strategy for Vergence Dysfunction............. 54

Convergence

Insufficiency...................................... 54

Divergence

Excess .................................................. 56

Basic

Exophoria ...................................................... 56

Convergence

Excess ............................................... 56

Divergence

Insufficiency ........................................ 57

Basic Esophoria ...................................................... 57

Fusional

Vergence

Dysfunction .............................. 58

Vertical

Phorias....................................................... 58

Patient

Education.............................................................. 58

Prognosis

and Followup ................................................... 58

CONCLUSION

................................................................................................ 61

III. REFERENCES

.................................................................................. 62

IV. APPENDIX

........................................................................................ 79

Figure 1:

Control Theory of Accommodative and Vergence

Interactions....................................................................... 79

Figure 2:

Potential Components of the Diagnostic Evaluation for

Accommodative and Vergence Dysfunction.................... 80

Figure 3:

Optometric Management of the Patient with

Accommodative Dysfunction: A Brief Flowchart .......... 81

Figure 4:

Optometric Management of the Patient with Vergence

Dysfunction: A Brief Flowchart ..................................... 82

Figure 5:

Frequency and Composition of Evaluation and

Management Visits for Accommodative or Vergence
Dysfunction...................................................................... 83

Figure 6:

ICD-9-CM Classifications of Accommodative and

Vergence Dysfunction ..................................................... 85

Abbreviations of Commonly Used Terms ........................................... 88

Glossary............................................................................................... 89

Statement of the Problem 3

STATEMENT OF THE PROBLEM

In previous generations, when survival depended on the ability to hunt,
fish, and farm, the visual system had to respond to constantly changing,
distant stimuli. Good distance visual acuity and stereoscopic vision were
of paramount importance. Today, the emphasis has shifted from distance
to two-dimensional near vision tasks such as reading, desk work, and
computer viewing. In some persons, the visual system is incapable of
performing these types of activities efficiently either because these tasks
lack the stereoscopic cues required for accurate vergence responses or
because the tasks require accommodative and vergence functioning that
is accurate and sustained without fatigue. When persons who lack
appropriate vergence or accommodative abilities try to accomplish near
vision tasks, they may develop ocular discomfort or become fatigued,
further reducing visual performance.

Accommodative and vergence dysfunctions are diverse visual anomalies.
Any of these dysfunctions can interfere with a child's school
performance, prevent an athlete from performing at his or her highest
level of ability, or impair one's ability to function efficiently at work.
Those persons who perform considerable amounts of close work or
reading, or who use computers extensively, are more prone to develop
signs and symptoms related to accommodative or vergence dysfunction.
Symptoms commonly associated with accommodative and vergence
anomalies include blurred vision, headache, ocular discomfort, ocular or
systemic fatigue, diplopia, motion sickness, and loss of concentration
during a task performance. The prevalence of accommodative and
vergence disorders, combined with their impact on everyday activities,
makes this a significant area of concern.

An accommodative or vergence dysfunction can have a negative effect
on a child's school performance, especially after third grade when the
child must read smaller print and reading demands increase. Due to
discomfort, the child may not be able to complete reading or homework
assignments and may be easily distracted or inattentive. Such children
may not report symptoms of asthenopia because they do not realize that
they should be able to read comfortably. The clinician should suspect a

4 Accommodative and Vergence Dyxfunction

binocular or accommodative problem in any child whose school
performance drops around third grade or who is described as

inattentive.1

Many children who have reading problems or who are learning disabled

or dyslexic have accommodative and vergence problems.2-4 Even if one
of these ocular conditions is not the primary factor in poor academic
performance, it can contribute to a child's difficulty with school work;
therefore, any child who is having academic problems should have a
comprehensive optometric examination. If indicated by signs or
symptoms, optometric vision therapy to improve accommodative and
binocular skills may enable the child to perform near tasks more
comfortably and benefit more effectively from educational remediation.

Good binocular skills contribute to better athletic performance. Sports
such as basketball, baseball, and tennis require accurate depth perception,
which in turn depends upon good binocularity. Studies show that tennis
players have significantly lower amounts of and more stable heterophoria

than nonathletes5 and that varsity college athletes have better depth

perception than nonathletes.6

The increased use of computers in the workplace, and in schools, has
focused attention on the impact of binocular vision dysfunction on both
performance and comfort. A high percentage of symptomatic computer

workers have binocular vision problems7 and ocular discomfort

increases with the extent of computer use.8-10 Similar findings are
reported for other populations who perform sustained near work, such as
students, accountants, and lawyers. Asthenopia associated with
sustained near work can usually be eliminated with proper lens
correction or vision therapy to improve accommodative-convergence
function.

Description and Classification of Accommodative and
Vergence Dysfunction

Although clinicians attempt to classify their vision problems, many
patients do not fit perfectly into specific diagnostic categories. Most

Statement of the Problem 5

symptomatic patients have defects in more than one area of binocular
vision. For example, the patient with vergence dysfunction may have a
secondary accommodative problem, while one with an accommodative
problem may have a secondary vergence problem, because the
accommodative and vergence systems are controlled by an interactive

negative feedback loop,11 as depicted in Appendix Figure 1. Blur and
unresolved disparity vergence errors are used to activate the system to
eliminate residual blur and disparity vergence errors. The ICD-9-CM
classification of accommodative and vergence dysfunction is shown in
Appendix Figure 6.

1. Accommodative

Dysfunction

This Guideline uses the Duke-Elder classification of accommodative

dysfunction.12

a. Accommodative

Insufficiency

Accommodative insufficiency occurs when the amplitude of
accommodation (AA) is lower than expected for the patient's age and is

not due to sclerosis of the crystalline lens.12,13 Patients with
accommodative insufficiency usually demonstrate poor accommodative
sustaining ability.

b. Ill-Sustained

Accommodation

Ill-sustained accommodation is a condition in which the AA is normal,

but fatigue occurs with repeated accommodative stimulation.12,13

c. Accommodative

Infacility

Accommodative infacility or accommodative inertia occurs when the
accommodative system is slow in making a change, or when there is a
considerable lag between the stimulus to accommodation and the

accommodative response.13 The patient often reports blurred distance
vision immediately following sustained near work. Some have

considered this infacility to be a precursor to myopia.14

6 Accommodative and Vergence Dyxfunction

Paralysis of Accommodation

Paralysis of accommodation is a rare condition in which the
accommodative system fails to respond to any stimulus. It can be caused
by the use of cycloplegic drugs, or by trauma, ocular or systemic disease,

toxicity, or poisoning.13 The condition, which can be unilateral or
bilateral, may be associated with a fixed, dilated pupil.

Spasm of Accommodation

The result of overstimulation of the parasympathetic nervous system,
spasm of accommodation may be associated with fatigue. It is
sometimes part of a triad (overaccommodation, overconvergence, and

miotic pupils) known as spasm of the near reflex (SNR).15 This
condition may also result from other causes, such as the use of either
systemic or topical cholinergic drugs, trauma, brain tumor, or myasthenia
gravis.

2. Vergence

Dysfunction

The classification of vergence dysfunction is based on a system

originally developed by Duane for application to strabismus.16 The
system has been modified for the classification of heterophoria and
intermittent strabismus (Table 1).

Statement of the Problem 7

Table 1

Modified Duane Classification System*

Convergence insufficiency

X < X'

Low AC/A ratio

Receded near point of convergence, reduced fusional convergence

Divergence excess

X > X'

High AC/A ratio

High tonic exo

Large exophoria/tropia at distance

Basic exo

X = X'

Normal AC/A ratio

Convergence excess

E < E'

High AC/A ratio

Divergence insufficiency

E > E'

Low AC/A ratio

High tonic eso

Basic eso

E = E'

Normal AC/A ratio

Vergence insufficiency

Normal AC/A ratio

Restricted fusional vergence amplitudes

Steep fixation disparity curve

8 Accommodative and Vergence Dyxfunction

Vertical phorias
Comitant

deviations

Noncomitant

deviations

Old decompensated 4th nerve palsies

Newly acquired 4th nerve palsies

Legend: X = exophoria at distance; E = esophoria at distance;
X' = exophoria at near; E' = esophoria at near

Modified from Duane A. A new classification of the motor anomalies of
the eye, based on physiologic principles. Part 2. Pathology. Ann
Ophthalmol Otolaryngol 1897; 6:247-60.

a. Convergence

Insufficiency

Classic convergence insufficiency (CI) consists of a receded near point
of convergence (NPC), exophoria at near, reduced positive fusional
convergence (PFC), and deficiencies in negative relative accommodation

(NRA).16 However, not all patients with CI have all of these clinical
findings. CI can be described as a deficiency of PFC relative to the
demand and/or a deficiency of total convergence, as measured by the

NPC.17

b. Divergence

Excess

Divergence excess (DE) can be described clinically as exophoria or
exotropia at far greater than the near deviation by at least 10 prism

diopters (PD).18

Statement of the Problem 9

c. Basic

Exophoria

The patient with basic exophoria has a deviation of similar magnitude at

both distance and near.19,20

d. Convergence

Excess

The patient with convergence excess (CE) has a near deviation at least 3

PD more esophoric than the distance deviation.21 The etiology of the
higher eso deviation at near most commonly is indicated by a high
accommodative convergence/accommodation (AC/A) ratio.

e. Divergence

Insufficiency

In a patient with divergence insufficiency (DI) tonic esophoria is high

when measured at distance but less at near.22 Symptomatic patients
usually have low fusional divergence amplitudes at distance and low
AC/A ratios.

f. Basic

Esophoria

The patient with basic esophoria has high tonic esophoria at distance, a

similar degree of esophoria at near, and a normal AC/A ratio.16

Fusional Vergence Dysfunction

Patients with fusional vergence dysfunction (vergence insufficiency)
often have normal phorias and AC/A ratios but reduced fusional

vergence amplitudes.23 Their zone of clear single binocular vision
(CSBV) is small.

h. Vertical

Phorias

Vertical phorias may be either comitant and idiopathic or noncomitant,

due to muscle paresis or other mechanical cause.24 One of the most
common causes of newly acquired vertical diplopia or asthenopia with
vertical deviation is longstanding, decompensated, fourth nerve palsy,

10 Accommodative and Vergence Dyxfunction

which results in superior oblique paresis. These patients demonstrate a
hyperphoria in primary gaze that is initially greatest during depression
and adduction of the affected eye. Over time, secondary overaction and
contracture of the inferior oblique muscle may overshadow the initial
fourth nerve palsy. Thus, the deviation may be largest during elevation
and adduction of the affected eye.

Epidemiology of Accommodative and Vergence Dysfunction

1. Accommodative

Dysfunction

a. Prevalence

Accommodative dysfunction has been reported to occur in 60 to 80

percent of patients with binocular vision problems;25,26 however, few
studies have been conducted to determine the prevalence of
accommodative dysfunction in the general population. An investigation
of the prevalence of symptomatic accommodative dysfunction in
nonpresbyopic patients examined in an optometry clinic found that 9.2
percent of these patients had accommodative insufficiency, 5.1 percent
had accommodative infacility, and 2.5 percent had accommodative

spasm.25

b. Risk

Factors

Most nonpresbyopic accommodative disorders originate from the need to
sustain the increased accommodation required for viewing two-
dimensional targets at near. Sustaining accommodation can fatigue the
accommodative system. One theory suggests that the cause of
accommodative fatigue is accommodative adaptation or slow

accommodation.27

Accommodation can be affected by a number of drugs and by diseases
(e.g., diabetes mellitus, myasthenia gravis).

Statement of the Problem 11

2. Vergence

Dysfunction

a. Prevalence

There are conflicting estimates of the exact prevalence of vergence
anomalies because clinicians and researchers use different definitions of
these conditions and different methods of analysis.

•

Convergence insufficiency.

CI is the most common vergence

anomaly. The reported prevalence of CI is 1 to 25 percent of

clinic patients.16,17,28,29 The median prevalence of CI in the
population is 7 percent, and it is similar for adults and

children.17

A report that 5 percent of a school-age population have reduced NPC and
6 percent fail a cover test used the following criteria for failure: at near,
more than 5 PD esophoria, 9 PD exophoria, or 1 PD vertical phoria; at
far, more than 5 PD esophoria, 5 PD exophoria, or 2 PD vertical

phoria.14 The findings were similar in the young adult population. The

ratio of females to males with CI is 3:2.30

•

Divergence excess.

The prevalence of DE is approximately 0.03

percent of the population, and it is more common in women and

blacks.18 DE strabismus has a strong hereditary

predisposition.18

•

Convergence excess.

One study of an urban population reported

that 5.9 percent of patients seeking optometric care had CE,25
and another found a 7.1 percent prevalence in a pediatric

population.31

•

Divergence insufficiency.

DI is probably the least common

vergence dysfunction. The only report on its prevalence came
from a study of urban pediatric patients seeking optometric care,

which showed a prevalence of 0.10 percent.31

12 Accommodative and Vergence Dyxfunction

•

Basic exophoria and esophoria.

One study of 179 patients with

exo deviation found that 62 percent had CI and 27 percent had

basic exophoria.32 Based on the prevalence of CI
(approximately 7 percent), the interpolated prevalence of basic
exophoria is 2.8 percent of the population.

•

Fusional vergence dysfunction.

One report ranks the

prevalence of this condition just below those of CI and CE.33

•

Vertical phorias.

Early estimates of the prevalence of vertical

deviations ranged from 7 percent34 to 52 percent.35 A recent
estimate of the prevalence of vertical phorias is about 20 percent

of the population.36 The reported prevalence differs on the basis
of criteria used to diagnose a clinically significant vertical
phoria. Only about 9 percent of vertical phorias are clinically

significant.24

b. Risk

Factors

Many patients with vergence anomalies are asymptomatic. Symptoms
usually occur when the visual environment is altered, specifically, when
near work is increased in situations such as school, work, and computer
use. Patients with low pain thresholds tend to be more symptomatic,
while patients who suppress an eye tend to be less symptomatic.

Defects in vergence may also be the result of trauma and certain systemic
diseases. For example, CI and fourth nerve palsy are common after

closed head trauma, especially in the presence of a concussion.37-39 CI

is the most common vergence dysfunction found with Graves disease.40
Myasthenia gravis may present as a CI or any other fusional vergence
disorder. Fusional vergence disorders are often associated with

Parkinson disease and Alzheimer disease.41,42

Statement of the Problem 13

Clinical Background of Accommodative and Vergence
Dysfunction

1. Accommodative

Dysfunction

a. Natural

History

Accommodation, which provides the retina with a clear, sharp image,

develops by 4 months of age.13 The primary stimulus for
accommodation is blur, with lesser roles played by apparent perceived
distance, chromatic aberration, and spherical aberration. During
accommodation, the ciliary muscle contracts, relaxing the tension on the

zonular fibers.43 This relaxation increases the convexity of the anterior
surface of the lens. If the system does not respond accurately, a negative
feedback loop repeats the process and reduces the error. This process
continues until the error is reduced to as near zero as possible. With age,
the lens fibers and lens capsule lose their elasticity and the size and shape

of the lens increase.44 This sclerosis of the lens causes presbyopia and a
reduction in AA.

The accommodative response is the actual amount of accommodation by
the lens for a given stimulus. It is usually the least accommodation
required to obtain a clear image. It is limited by the depth of focus
(which is dependent on pupil size) and the inability to detect small

amounts of blur.45 At distance, the system usually overaccommodates,
while at near the system usually underaccommodates, creating a lag in
accommodation. The resting state of accommodation is not at infinity
but at an intermediate distance that varies from individual to individual
within a range of 0.75 to 1.50 diopters (D). The resting state is similar to
the accommodation measured in night myopia or empty field

myopia.46,47

Sustained accommodative effort has been reported to cause
accommodative fatigue and asthenopia. In some individuals, the
punctum proximum recedes after repeated push-up stimulation of

accommodation.48 One study showed that the amplitude of
accommodation increased in 29 percent of the subjects after sustained

14 Accommodative and Vergence Dyxfunction

push-ups, while in 31 percent there was a decrease in amplitude and an

associated blur.49 Repeated near-far stimulation does not affect the AA

in most subjects.50 The few subjects who demonstrated fatigue also

reported asthenopia that was not age dependent.50 From these studies it
can be concluded that the accommodative system is resistant to fatigue in
most individuals. However, in patients who demonstrate fatigue,
asthenopia usually ensues.

Common Signs, Symptoms, and Complications

•

Accommodative insufficiency.

Patients with accommodative

insufficiency often complain of blurred vision, difficulty reading,
irritability, poor concentration, and/or headaches. Attempting to
accommodate, some patients may stimulate excessive
convergence by the AC/A crosslink and be incorrectly classified
as having CE.

In accommodative insufficiency, the AA is less than expected for the
patient's age. Patients with accommodative insufficiency usually fail the
+/- 2.00 D flipper test and have positive relative accommodation (PRA)
under -1.50 D. These patients may be able to make appropriate
accommodative responses, but they expend so much effort that
asthenopia ensues. They may complain about blur after sustained
reading or at the end of the day. The fast accommodative mechanism
becomes fatigued and the slow adaptive accommodative mechanism
takes over, resulting in blur.

•

Ill-sustained accommodation.

The most common sign or

symptom of ill-sustained accommodation is blurred vision after
prolonged near work. It occurs because the accommodative
system fails to sustain long-term accommodative effort. In ill-
sustained accommodation which is similar to accommodative
insufficiency, except that the AA is normal, the patient generally
fails the +/-2.00 D flipper test and has a decreased PRA. In
addition, such patients often have asthenopia.

Statement of the Problem 15

•

Accommodative infacility.

Patients with accommodative

infacility report that after prolonged near focusing, their distance
vision is blurred and/or that, after prolonged distance viewing,
reading material is blurred. These patients invariably fail the +/-
2.00 D accommodative facility test monocularly and binocularly.
They have normal AAs, but they may have abnormal relative
accommodative findings, PRA or NRA.

•

Paralysis of accommodation.

Paralysis of accommodation

results when a nonpresbyopic patient loses the ability to
accommodate either monocularly or binocularly. The chief
complaint is blur due to failure to accommodate, and there may
be associated micropsia. Paralysis can be the result of trauma,
toxicity, Adie's pupil, neuropathy, and/or drugs, such as
cycloplegic agents. The etiology of the paralysis should be
identified if possible.

•

Spasm of accommodation.

Spasm of accommodation occurs

when the accommodative system inappropriately
overaccommodates for a stimulus. It is most often secondary to
constant parasympathetic innervation as part of the SNR but its
origin is usually not associated with serious organic disease.
Spasms as great as 25 D have been reported, and distance vision
is usually impaired. One study reported that for most patients
with this disorder, the etiology is probably psychogenic. Some
clinicians use the term "accommodative excess" interchangeably

with "accommodative spasm."15

Early Detection and Prevention

Although early detection and treatment are ideal, there is no evidence
that early treatment affects the long-term use or disuse of the
accommodative system. However, early detection is important when the
AC/A ratio is high and accommodation results in an esotropia at near.
Early examination of children is important to detect and eliminate both
accommodative and vergence dysfunction because these anomalies may
affect future school performance adversely. The child's first eye and
vision examination should be scheduled just after 6 months of age.

16 Accommodative and Vergence Dyxfunction

When no abnormalities are detected at this age, the next examinations
should be scheduled at age 3 and before the first grade (age 6).

2. Vergence

Dysfunction

a. Natural

History

Rapid, accurate eye movements are necessary to fixate and stabilize a
retinal image. It is imperative to maintain a fixed retinal image to
stabilize the visual world during body movement. The eyes and the neck
work together to localize and stabilize an image by optokinetic and
vestibular reflexes. These reflexes provide a platform from which

voluntary eye movements are executed.51 Several components are
required to maintain fixation and to shift the line of sight to a new point
of interest: an accurate, efficient, smooth pursuit system to hold a
moving target on the fovea; a saccadic system to bring the fovea to the
object of regard; and a vergence system to place the object of regard on
both foveas while looking from near to far.

To maintain exact alignment, the eyes must incorporate disjunctive
movements into the scheme of normal conjugate movements. These
movements must be extremely accurate to avoid diplopia and facilitate a
unified perception. Two different types of stimuli initiate these
disjunctive movements: retinal disparity for vergence movements and

defocused (blurred) objects for accommodative responses.52

Two different types of fusional vergence have been described: (1) a fast,
reflexive vergence system driven by retinal disparity and (2) a slow,

adaptive system which receives its input from the fast system.11 The
slow system is also known as vergence adaptation. Theoretically,
heterophoria is a vergence error that is eliminated by fusional or disparity
vergence. Slow vergence reduces the stress or load placed on the fast
vergence system by heterophoria during binocular viewing. Total
fusional vergence is equal to the sum of the fast and slow systems.

Refer to the Optometric Clinical Practice Guideline for Pediatric Eye and Vision

Examination.

Statement of the Problem 17

The initial response to a new vergence demand is initiated by the fast,
disparity-driven vergence system. Upon attainment of fusion, the output
from the fast fusional system decreases; the output from the slow
vergence system increases proportionally. Once adaptation has occurred,
total fusional vergence is supplied by the slow vergence system and the
residual fast vergence. The residual error from the initiation of a new
disparity vergence response is the fixation disparity (FD). Thus, the slow
vergence system is responsible for sustaining CSBV during prolonged
reading or other near tasks. It is failure of the slow vergence system that
results in asthenopia.

•

Convergence insufficiency.

The etiology of CI is controversial.

It probably results from a breakdown in the accommodative-

convergence relationship.17,53-55 It is likely that a genetic
predisposition for CI exists because the parents of children with
CI often have the condition. Symptoms tend to occur when
persons use their eyes in a two-dimensional reading environment
for extended periods of time. The symptoms tend to increase
during the teenage years and continue to increase during the
early twenties. Symptoms commonly occur with computer use

or in a visually demanding work environment.8-10,17,56,57

Most patients with CI have normal stereopsis but may exhibit
suppression when viewing first-degree fusion targets. It is not
uncommon for the CI patient to manifest an exotropia during near point
testing without reporting diplopia. When an eye deviates, the patient
may report blurred vision or suppress the eye. Suppression provides a
mechanism of eliminating diplopia or asthenopia.

Patients with CI generally have poor fusional convergence ability,
compared with the magnitude of their exophoria. Typically, they do not
meet Sheard's criterion (i.e., a fusional vergence reserve at least twice the

magnitude of the heterophoria).17,58,59 Many patients with CI also

have poor accommodative facility.17,60 In some instances, CI results
from the accommodative system's failure to accommodate accurately at
near. The inability to obtain an appropriate accommodative response

18 Accommodative and Vergence Dyxfunction

results in an exodeviation at near because of a low AC/A ratio. Patients
experiencing this phenomenon have been called "pseudo-CI patients."

•

Divergence excess.

The most widely accepted theory of the

etiology of DE involves innervation and is based upon the use of
the eyes. According to this theory, divergence is active and

purposeful, and it occurs in the absence of stereoscopic cues. 18
The deviation may present as a heterophoria or a strabismus. It
has been suggested that the deviation extends the peripheral field

of view when the patient manifests a strabismus.18 The
deviation is often first noticed in children under 18 months of

age.61 Progression may occur throughout life, but at about 6
years of age, the deviation becomes more noticeable because of
an increase in both the frequency and extent of the deviation.

•

Basic exophoria.

The clinical findings of the patient with basic

exophoria are similar to those of the DE patient. Basic
exophoria is thought to occur in a patient with DE who develops
secondary CI. The extent of the deviation tends to increase with
age at both distance and near.

•

Convergence excess

. CE is due to a high AC/A ratio.62 The

angle of deviation is usually stable until school age, when it
tends to increase.

•

Divergence insufficiency

. This condition is due to high tonic

esophoria and tends not to change with time.

•

Basic esophoria

. Little is known about the natural history of

basic esophoria. The condition is presumed to be due to tonic
vergence errors, such as DI which develops early in life (at about
6-9 months of age). Deficits related to an abnormal
accommodative vergence system first occur at about 2 years of
age. Basic esophoria is probably due to an abnormal gain in
output from the neuromuscular system (i.e., high AC/A ratio). A
genetic predisposition for basic esophoria seems to exist in a
significant proportion of those who have it.

Statement of the Problem 19

•

Fusional vergence dysfunction.

The etiology of fusional

vergence dysfunction is uncertain. The patient often first notices
it when asthenopia occurs.

•

Vertical Phorias

. Vertical deviations have three different

origins; therefore, patients can present with three different
histories. Congenital or early acquired comitant hyperdeviations
are usually small in magnitude and nonprogressive over time.
Congenital fourth nerve palsies, which decompensate over time,
may be first noted after an insult, such as a high fever or trauma.
Newly acquired fourth nerve palsies occur after vascular,

infectious, traumatic, or neoplastic incidents.63 Depending on
the etiology of the vertical deviation, its course may change.
Deviations that occur secondary to vascular or ischemic
involvement tend to improve with time; those caused by trauma
may remain stable; and those of neoplastic origin usually
worsen.

Common Signs, Symptoms, and Complications

Most patients report symptoms of vergence dysfunction during their
second through fourth decades of life, when they have the greatest
amount of near work. Eliciting symptoms from patients can sometimes
be difficult, especially when the patients are very young children. Many
patients with chronic problems have learned to live with their condition
and may not voluntarily reveal their symptoms. Children may have
fewer near vision needs; more importantly, many are unable to describe
their symptoms. Young children may not report symptoms because they
consider diplopia and asthenopia normal. During the formative school
years, the additional load on the visual system may result in avoidance of
near tasks, such as reading. The relationship between asthenopia and
school performance is governed, to some extent, by pain thresholds. The
increase in symptoms reported by young adults is probably related to
increased severity of chronic symptoms that have been present most of
their academic lives.

Presbyopic patients may demonstrate vergence dysfunction due to the
loss of accommodative convergence or due to prism induced through

20 Accommodative and Vergence Dyxfunction

their bifocals. Those who are symptomatic generally have poor fusional
convergence and poor slow (adaptive) vergence abilities. Patients with
vergence anomalies may have the following symptoms: asthenopia,
headaches, pulling sensation, blurred vision, intermittent diplopia,
inability to sustain concentration, pulling of the eyes, and burning or
tearing of the eyes. Symptoms tend to increase by the end of the day and
are related to the use of the eyes.

•

Convergence insufficiency.

The most common symptoms

associated with CI are blurred vision, diplopia, a gritty sensation
of the eyes, discomfort associated with near work, frontal
headaches, pulling sensation, heavy eyelids, sleepiness, loss of
concentration, nausea, dull ocular discomfort, and general
fatigue. Some patients with CI report decreased depth
perception. A significant number of patients with CI complain

of motion sickness or car sickness.17 A high percentage of
patients with CI have emotional problems and anxiety reactions,
and it has been suggested that all symptomatic CI results from

psychosis and emotional problems.64,65 However, there is no
evidence to substantiate this theory, although it is possible that

CI may cause nervousness, tension, and anxiety.17

Most patients with CI have a low PFC amplitude (10 PD or less).17 One
study reported that 79 percent of all patients with CI have an exophoria

at near, while 18 percent are orthophoric and 3 percent are esophoric.56
Another study found that 63 percent of patients with CI have an

exophoria.66

Symptomatic CI patients have poor prism adaptation and slow vergence
ability. Recovery values, which represent voluntary convergence, also
may be below normal. The NPC, which is receded in most CI patients,

represents the most consistent finding.55,67 Other clinical findings
include low AC/A ratio, low NRA, and failure with plus lenses or the +/-
2.00 D accommodative facility test.

Statement of the Problem 21

•

Divergence excess

. The patient with DE may be asymptomatic.

When the deviation occurs with either deep suppression or
anomalous correspondence, asthenopia is not usually present.
However, if either suppression or anomalous correspondence has
failed to develop, diplopia or asthenopia generally ensues. The
closing of an eye in bright sunlight may be pathognomonic of
DE. Some DE patients complain of distance blur because they
overaccommodate to keep their eyes aligned. Common clinical
findings associated with DE include normal NPC, adequate PFC
at near, equal vision in each eye, and normal stereopsis at

near.68

When the eyes of a patient with DE deviate, any of a variety of sequelae-
-e.g., suppression, diplopia with normal retinal correspondence (NRC),
anomalous retinal correspondence (ARC) with single vision--may

occur.69 If ARC occurs when the eye deviates, the DE patient has an

extension of the binocular field known as panoramic viewing.69 Retinal
projection shifts to match the objective angle (harmonious ARC). There
may be little or no foveal suppression during deviation because each
fovea has its own unique visual direction.

•

Basic exophoria.

The most common symptoms of basic

exophoria are related to asthenopia. The clinical findings of
basic exophoria are similar to those of DE because the basic
exophoric patient is considered to be a DE patient who acquires
CI. Thus, like the DE patient, the patient with basic exophoria
may have no symptoms.

•

Convergence excess.

Symptoms of CE include blurred vision,

diplopia, headaches, and difficulty concentrating on near tasks.
Symptomatic patients with CE have low fusional divergence
amplitudes and PRAs in relationship to their near point demands.
Not all patients with CE present with symptoms. Some patients
with CE suppress, some have strong vergence adaptation, and
some have a high pain threshold, while others have no symptoms

because they avoid near work.70

22 Accommodative and Vergence Dyxfunction

•

Divergence insufficiency.

Symptomatic patients with DI

usually have reduced fusional divergence amplitudes at distance.
They also have low AC/A ratios. Such patients often report
diplopia or blur at distance.

•

Basic esophoria.

Patients with basic esophoria are symptomatic

only when their fusional divergence amplitudes are not large
enough to compensate for the esophoria. Moreover, symptoms
may not occur in the patient who suppresses. Because the
deviation is present at all distances, the symptoms are generally
the same with either far viewing or near viewing.

•

Fusional vergence dysfunction.

Some patients with vergence

anomalies do not have significant heterophorias present at any
distance; instead, like patients who have CI, they present with
asthenopia. If appropriately questioned, these patients generally
report asthenopia during vergence testing. They usually have
reduced fusional vergence amplitudes (fast vergence) in both
convergence and divergence directions. In addition, these
patients usually have accompanying accommodative problems.
Typically, the fixation disparity curve (FDC) is very narrow,
with a small flat zone indicating poor vergence adaptation.

•

Vertical phorias.

Diplopia is the typical presenting sign of the

patient who has a significant vertical deviation. The patient may
also have a head tilt and/or asthenopia as a result of trying to
maintain single, binocular vision. The patient with a recent-
onset vertical deviation has a normal break and recovery
(approximately +3 D of vertical fusional amplitude, as measured
from the heterophoria), while those with longstanding vertical
deviations usually have abnormally large opposing vertical
fusion ranges. The high opposing vertical fusional vergence
amplitudes are associated with a robust, slow vergence system.

The Care Process 25

II. CARE

PROCESS

Diagnosis of Accommodative and Vergence Dysfunction

The evaluation of a patient with accommodative and vergence
dysfunction may include, but is not limited to, the following areas. The
examination components described are not intended to be all inclusive.
Professional judgment and the individual patient's symptoms and
findings have a significant impact on the nature, extent, and course of the
services provided. Some components of care may be delegated (see
Appendix Figure 2).

1. Patient

History

The patient history is the initial component of the examination and an
important part of making an appropriate diagnosis. A good history
should lead to a tentative diagnosis, which the examination will either
confirm or disprove. A suggested history to investigate accommodative
and vergence problems is shown in Table 2.

26 Accommodative and Vergence Dyxfunction

Table 2

Suggested Questions for Patient History

Do your eyes bother you?

If yes, how often and under what circumstances?

How do your eyes bother you?

Do you experience eyestrain, fatigue, headaches, sleepiness, etc.,
associated with near tasks?

Do you ever get headaches?

If yes, explore further (e.g., frequency, location, type, and
associated activities).

How long can you read comfortably?

Have the patient specify an actual time.

When you read, does the print ever blur, double, or move around?

Do you experience car or motion sickness?

________________________________________________________

2. Ocular

Examination

The simplest way to evaluate the relationship of accommodation and
vergence to asthenopia is to place stress on the visual system during the
examination in an attempt to produce asthenopia. The clinician should
be as concerned with the patient's reaction to testing as with the absolute
values obtained. Accommodative and vergence measurements may be
more revealing at the end of the day when fatigue is more likely to occur.
Futhermore, even with normal fusional vergence amplitudes, some
patients complain of asthenopia when tested with lenses and prisms.
Because this finding is diagnostic of an accommodative-vergence
anomaly, one goal of testing is to create asthenopia similar to that which
occurs during normal day-to-day activities.

The Care Process 27

Normally, all components of vergence and accommodation are
synergistic; accommodation, convergence, and pupillary miosis occur in
synchrony. Procedures that isolate these individual functions by holding
one function constant actually measure the plasticity or flexibility of the
system. Patients who demonstrate poor plasticity or flexibility often are
those who experience symptoms. Measurements are influenced by the
size of the target, illumination, speed of measurement, and the effort

exerted by the patient.76 When taking any clinical measurement, the
optometrist should encourage the patient to exert maximum effort. The
clinician should record any asthenopic complaints induced by the
measurements. Patients who become uncomfortable or fatigued by
testing are usually symptomatic in everyday life.

a. Visual

Acuity

The best corrected visual acuity should be measured for each eye
individually and for both eyes together, at distance and near. Variability
between distance and near visual acuity may indicate an accommodative
anomaly. Some patients with accommodative dysfunction report that
their vision fluctuates, especially after prolonged near tasks. When
visual acuity is better monocularly than binocularly, the clinician should
suspect vergence dysfunction.

b. Refraction

The patient's refractive status should be evaluated. Patients with
uncorrected hyperopia--especially latent hyperopia--often have
accommodative dysfunction because accommodation compensates for
the hyperopia. Cycloplegic refraction is advised for the patient who
could have an excessive accommodative response that could affect the
measurement of refractive error.

28 Accommodative and Vergence Dyxfunction

Ocular Motility and Alignment

Cover testing should be performed with a small target to control

accommodation.77 The eye should be occluded for a minimum of 2
seconds to elicit any existing deviation. During unilateral testing, the
clinician should pay careful attention to the movement of the fellow eye
and, upon alternate cover testing, to the movement of the uncovered eye.
Both the extent of the deviation and the quality of fusion should be
noted. Any significant deviation seen upon alternate cover testing should
be neutralized with prisms. When the patient has poor fixation, a muscle
light (penlight or transilluminator) can be substituted for an
accommodative target.

In the evaluation of ocular motor function, versions should be performed
to rule out paresis, paralysis, overaction, or underaction of a muscle.
Careful attention should be given to lateral fields of gaze especially
during elevation and adduction. Defects associated with overaction of
the inferior oblique muscles, superior oblique palsy, Brown's syndrome,
and V syndromes are apparent in these fields of gaze. When the clinician
has difficulty evaluating motor response in a particular field of gaze, the
alternate cover test with prism neutralization should be performed in that
field.

The heterophoria may also be measured using Risley prisms in a
phoropter, or in free space at both distance and near, using an
accommodative target. When a torsional component is suspected, the
patient can be asked whether the two test targets are parallel. Other
methods that can be used to measure heterophoria include the Maddox
rod and stereoscopic devices.

Near Point of Convergence

The NPC test is important for assessment of binocular function. It is best

performed using a small accommodative target.78 The break and
recovery, as well as any discomfort evoked by testing, should be
recorded. The patient who grimaces, moves away from the target, or is
bothered by the test is usually symptomatic. The test should be repeated
several times if necessary. If the patient cannot provide good verbal

The Care Process 29

responses or demonstrates suppression (denoted by not reporting diplopia
upon deviation), the clinician should use a penlight to observe the
corneal reflexes. Placing a red lens over one eye and repeating the NPC
measurement 4 or 5 times will often cause a fragile binocular system to

break down and the NPC to recede.79

Near Fusional Vergence Amplitudes

Positive and negative fusional vergence amplitudes are measures of the
amount of prism that can be placed in front of the eyes before the patient
reports a sustained blur. Once blur is reported, the patient is no longer
using only fusional vergence to maintain single binocular vision, but is
also employing accommodative vergence. The measurements may be
made with a Risley prism or prism bar. It is advantageous to use a prism
bar to observe the eyes of young children or verbally uncooperative
patients.

The order in which fusional vergence tests are administered may affect

subsequent measurement of vergence functions.80,81 If base-out (BO)
fusional vergence amplitudes are measured before base-in (BI)
amplitudes, the BI fusional amplitudes will be reduced and vice versa. In
addition, the position of the heterophoria may be influenced by the test
that precedes its measurement. Measurement of convergence amplitudes
before heterophorias may cause the heterophoria to appear more
esophoric or less exophoric. Thus, the heterophoria should be measured
first, followed by divergence amplitudes, and then convergence
amplitudes.

Divergence and convergence fusional amplitudes should be measured

using an accommodative target.82 The patient should be instructed to
keep the target single and clear and to report whether the test bothers his
or her eyes. This is important because many patients experience fatigue
associated with the exertion of maximum effort to keep the target single
and clear. In this regard it is extremely important to note the patient's
subjective symptoms. These tests should be repeated if the patient's
responses are equivocal.

30 Accommodative and Vergence Dyxfunction

f. Relative

Accommodation

Measurements

Positive relative accommodation and negative relative accommodation
are indirect assessments of the fusional vergence system. In the
measurement of relative accommodation, plus or minus lenses are added
binocularly over the lenses that fully correct any refractive error until the
patient reports either blur or diplopia. The end point is the amount of
accommodation (clinically, the stimulus to accommodation) that can be
increased or decreased with a fixed amount of convergence. When
minus lenses are placed in front of the eyes, accommodation occurs,
clearing the image. The eyes converge by the AC/A crosslink. In order
to maintain CSBV, the eyes must neutralize this accommodative
convergence by fusional divergence. At the limit of PRA, fusional
divergence is exhausted, and accommodation must be inhibited to reduce
convergence, resulting in blur. An analogous response occurs when plus
lenses are substituted for minus lenses in these assessments.

Accommodative Amplitude and Facility

AA may be measured monocularly, using either the push-up or the minus
lens method. Generally, the optometrist uses a 20/20 to 20/30 target and

notes the first sustained blur.83

Accommodative facility testing can be performed using a +/-2.00 D lens
flipper or a phoropter. The patient should be able to clear these lenses

monocularly within 11 cycles per minute without evidence of fatigue.84

Patients with accommodative infacility frequently report intermittent
blurred vision and asthenopia after near work. Symptomatic patients
demonstrate reduced accommodative facility on the +/-2.00 D flipper

test.13,85,86

h. Stereopsis

Stereopsis can be assessed and quantified using measures such as the
Randot or Titmus Stereo tests. Contour or line stereograms can be used
to measure stereoacuity. Appreciation of a random dot stereogram

The Care Process 31

requires both fusion and bifoveal fixation,87 thus, confirming that the
patient was not strabismic at the time of testing.

Ocular Health Assessment and Systemic Health Screening

Gross inspection of the eyelids and adnexa is important to rule out
abnormalities such as exophthalmos associated with Graves disease,
facial and orbital asymmetry, and ptosis. Biomicroscopy may also be
performed to rule out media abnormalities that may cause decreased
visual acuity. A dilated fundus examination may be needed to rule out
retinal and vitreal abnormalities. Certain systemic diseases (e.g.,
multiple sclerosis, diabetes mellitus, Graves disease, and myasthenia

gravis) can cause accommodative-vergence anomalies.88 Many
medications (e.g., tranquilizers, antidepressants, antispasmodics, and

motion sickness medications)89 can also cause accommodative
dysfunction.

3. Supplemental

Tests

When the comprehensive examination does not identify a cause for
asthenopia, the following tests may be helpful:

Accommodative Convergence/Accommodation Ratio

The AC/A ratio is a measure of the convergence induced by
accommodation per unit of accommodation. In a perfect physiological
system, accommodative convergence supplies all the necessary
convergence for near viewing. The normal AC/A ratio is 4:1.

Both high and low AC/A ratios have been implicated in binocular vision
problems. The two most popular methods of calculating the AC/A ratio
are the calculated distance-near deviation method and the gradient
method.

Distance-near method.

Many clinicians advocate using the calculated

distance-near method of determining the AC/A ratio because it takes into
account the actual position of the eyes during distance and near fixation.

32 Accommodative and Vergence Dyxfunction

Clinically, however, the calculation method suffers from the
noncalculated effects of the effort of accommodation, depth of field,
proximal accommodation and convergence, and blur interpretation.
Moreover, the calculation varies with fixation distance and interpupillary
distance (IPD). The AC/A ratio may be calculated by the following
formula:

AC/A ratio = convergence demand of near target - Hd + Hn

stimulus to accommodation of near target

Where: Hd

= Distance heterophoria

Hn1

= Near heterophoria

With this formula, an esophoria is a plus value, while an exophoria is
a minus value. Convergence demand is calculated by dividing the

IPD by 4 (e.g., 60/4 = 15).90

Alternatively,

AC/A ratio = IPD (cm) + N (Hn-Hd)

Where N is the near fixation distance in meters.

Gradient method.

The gradient method of calculating the AC/A ratio

uses the change in vergence angle at a given distance in association with
a change in the stimulus to accommodation produced by ophthalmic
lenses. Either plus (+1.00 D or +2.00 D) or minus (-1.00 D or -2.00 D)
lenses are placed in front of each eye. The heterophoria is remeasured
while the patient views the same target through the lens and the ratio is
calculated thus:

AC/A ratio = heterophoria 1 - heterophoria 2

lens power (D)

The Care Process 33

The AC/A is thought to be innate and stable until the beginning of

presbyopia;91 however, the stimulus and response to accommodation
differ. Theoretically, the response AC/A ratio may be estimated by

multiplying the stimulus AC/A ratio by 1.08.92

Fixation Disparity/Associated Phoria

Fixation disparity is the small misalignment of the eyes that occurs while
single binocular vision is maintained for the point of fixation. FD is a
direct measurement of this misalignment, and the associated phoria is the
amount of prism needed to neutralize the FD. Measurements of FD may
be obtained to determine the forced FDC, the associated phoria, and the
FDC. The chief advantage of the FD method over methods that interrupt
fusion is that it permits evaluation of the vergence system under
binocular conditions.

Distance Fusional Vergence Amplitudes

Distance fusional vergence amplitudes are determined in the same
manner as near vergence amplitudes, except that the targets are placed at
20 feet. The testing should be performed when the patient experiences
asthenopia or when a significant heterophoria is present with distance
fixation.

d. Vergence

Facility

Prism flippers may be used to test vergence facility. Normative values

have been established for 16 PD BO and 8 PD BI prisms.93 Mean
values are 8 cycles per minute for children ages 5-8 years and 13 cycles

per minute for children ages 7-14 years.93 Prism flippers may be used
when standard testing does not elicit a clearly defined reason for
asthenopia.

Accommodative Lag

The lag of accommodation is the difference between the stimulus of
accommodation and the response. It may be measured using binocular

34 Accommodative and Vergence Dyxfunction

cross-cylinders or near point retinoscopy, such as the monocular
estimated method (MEM).

MEM retinoscopy is performed by having the patient read grade-level
words at his or her habitual near working distance while the clinician
performs retinoscopy. The clinician rapidly interposes a lens in front of
the eye being evaluated and estimates the motion of the light reflex.
Lenses of various power are briefly interposed in this manner until
neutrality is found. Each lens is removed before an accommodative
response occurs. For most patients, the lag is between approximately
+0.25 D and +0.75 D. A lag of greater than +1.00 D is often found in
individuals with accommodative insufficiency or infacility, suggesting
the using of plus lenses at near. A lead of -0.25 D or more usually
indicates accommodative excess.

The fused cross-cylinder test is a subjective means of determining the lag
of accommodation. It is not as accurate as the MEM test and is often
difficult to perform in children under the age of 8 years.

4. Assessment

and

Diagnosis

The clinician can use the history and clinical findings to make the
diagnosis, assess the need for treatment, and determine the plan of
treatment. Clinical assessment has used the following protocols:

a. Graphical

Analysis

Graphical analysis is not a method of analyzing binocular function;
rather, it involves plotting test results to form a visual representation of

accommodation and vergence, and their interaction.94,95 The
relationship between accommodation and convergence can be
demonstrated by plotting five findings: distance and near heterophorias,
AC/A ratio, PFC, negative fusional vergence (NFV), and AA. The outer
boundaries of these measurements define the zone of CSBV.

The Care Process 35

Zones of Comfort

Several attempts have been made to develop clinical rules for the

prediction of asthenopia.59,96,97 One approach, suggested by

Sheard,59 takes the heterophoria into account and specifies that the
fusional vergence reserve should be twice the demand (i.e., heterophoria)
for sustained comfort. For example, for a patient with 10 PD of
exophoria, the base-out to blur measurement should be at least 20 PD. A
base-out to blur measuring only 8 PD would not meet Sheard's criterion.

Comparison to Expected Values

Accommodation and vergence findings can be statistically analyzed and
compared with normative values. The assumption is that any finding that
deviates from the norm by 2 standard deviations may indicate an
anomaly. Although this type of statistical analysis does not provide
correlative information with regard to asthenopia, it can alert the
clinician to a potential problem. Table 3 shows the most commonly used
norms for accommodation and vergence testing.

36 Accommodative and Vergence Dyxfunction

Table 3

Expected Values*

Measurements Mean S.D.

Range

Distance

Phoria

1 X

2 X

0-2 X

Base-in blur

Base-in break

5-9

Base-in recovery

3-5

Base-out blur

7-11

Base-out break

15-23

Base-out recovery

8-12

Near

Phoria

3 X'

5 X'

0-6 X

Base-in blur

11-15

Base-in break

19-23

Base-in recovery

10-16

Base-out blur

14-20

Base-out break

18-24

Base-out recovery

7-15

PRA

-2.25

.50

-1.75-+2.25

NRA +2.00

1.1

+1.75-+2.25

Gradient AC/A

4/1

3-5

16-(0.25

age)

+2.00 +1.0

Legend:

AA = Amplitude of accommodation; AC/A = Accommodative

convergence/accommodation ratio; NRA = Negative relative accommodation;

PRA = Positive relative accommodation;

X = exophoria at distance; X' = exophoria at near

Modified from Morgan MW. Analysis of Clinical Data. Am J Optom
1944; 21:477-91.

__________________________________________________________

The Care Process 37

Fixation Disparity and Vergence Adaptation

Small errors in vergence often occur during normal binocular fixation, in
which the eyes do not align exactly on the target. As long as the
vergence error does not exceed Panum's fusional area and the patient

does not report diplopia, this error is called FD.98 Controversy exists
regarding whether FD provides a purposeful error to stimulate the
vergence system, or whether it is an error-related indicator of a

malfunction of the vergence system.11,99 Proponents of the latter theory
have used FD measurements to determine the need for and amount of
prism to prescribe.

Although heterophoria and FD measures are often correlated, they often
differ as well. For example, some patients require only a small amount
of prism to neutralize a large horizontal FD, while others may require a
large amount of prism for neutralization of a small FD. Proponents of
FD methods have suggested that clinicians should prescribe the amount

of prism that neutralizes or eliminates the FD.100 FD neutralization
methods are probably more useful in measuring and prescribing for
vertical imbalances than for horizontal deviations. The prism prescribed
should be the least required to neutralize the horizontal and vertical

components of the FDC for 10 minutes.101

Comparison of Methods of Analysis

Evaluation of these methods of measurement of heterophoria, vergences,
and FDCs in symptomatic and asymptomatic patients has been

accomplished with the aid of discriminant analysis.102,103 The
application of Sheard's criterion was found to be any means of
identifying symptomatic exophoric patients. When the use of Sheard's
criterion does not differentiate asthenopic from nonasthenopic exophoric
patients, the angular measurement of FD has been found to be effective.
The absolute magnitude of esophoria was found to be most predictive of
asthenopia for esophoric patients; the second best measure of esophoria
is the NFV recovery value.

38 Accommodative and Vergence Dyxfunction

Management of Accommodative and Vergence Dysfunction

Management of the patient with an accommodative or vergence
dysfunction is based on such interpretation and analysis of the
examination results. Appendix Figures 3 and 4 provide an overview of
patient management strategies for accommodative and vergence
dysfunction, respectively.

Basis for Treatment

The general goals for treating accommodative and/or vergence
dysfunction are:

•

To assist the patient to function efficiently in school
performance, at work, and/or in athletic activities

•

To relieve ocular, physical, and psychological symptoms
associated with these disorders.

a. Vision

Therapy

•

Accommodative Therapy

. The purpose of accommodative

therapy is to increase the amplitude, speed, accuracy, and ease of
accommodative response. At the end of therapy the patient
should be able to make rapid accommodative responses without
evidence of fatigue. Studies of the effectiveness of vision
therapy for types of accommodative dysfunction are summarized
in Table 4.

The Care Process 39

Table 4

Effectiveness of Vision Therapy for Accommodative Dysfunction

Research Results

Accommodative Dysfunction

Study Authors

Summary/Interpretation

Cooper13

Berens & Stark49

Carr & Allen104

Sisson105

Accommodation can be
modified with training.

Berens & Stark49

Repeated accommodative
testing has been shown to
improve accommodative
responses.

Marg106

Voluntary accommodation
can be taught.

Cornsweet & Crane106

Accommodation developed
by biofeedback can transfer
from one task to another.

Accommodative insufficiency

Accommodative infacility

Sisson105

Morris108

Accommodative therapy has
been shown to be effective in
eliminating decreased
accommodative amplitude
and facility.

Hoffman et al26

In 87% of patients with
accommodative anomalies,
asthenopia was eliminated
and accommodative findings
were normalized with
approximately 26 therapy
sessions.

Daum109

Therapy to improve
accommodative amplitudes
can result in a concurrent
improvement of positive and
negative fusional amplitudes
and stereopsis.

40 Accommodative and Vergence Dyxfunction

Table 4 (Continued)

Accommodative Dysfunction

Study Authors

Summary/Interpretation

Vision therapy is the method
of choice in eliminating
asthenopic symptoms
associated with
accommodative anomalies.

For patients who cannot
participate in vision therapy,
plus lenses are often
successful in decreasing
symptoms.

Cooper et al 110

Monocular accommodative
amplitude therapy for
asthenopia patients effected
dramatic improvement in
accommodative amplitudes, a
reduction in accommodative
time constants, and a
significant reduction in
symptoms.

Randle & Murphy111

Liu et al 112

Vision therapy may result in
positive changes in the
magnitude, velocity, and gain
of accommodative responses.

Liu et al 112

Accommodative therapy not
only eliminates symptoms but
shows objective changes in
velocity of the
accommodative response and
a concurrent decrease in
recorded time constants.

Bobier & Sivak113

Vision therapy improves the
time characteristics of the
accommodative response,
including the latency and
velocity.

The Care Process 41

Several studies have reported that accommodation can be modified with

therapy.13,49,104,105 Repeated accommodative testing itself improves

accommodative responses.49 Studies have also shown that voluntary

accommodation can be taught106 and that accommodation skills

developed by biofeedback can transfer from one task to another.107

Accommodative therapy has demonstrated effectiveness in eliminating

decreased accommodative amplitude and facility.105,108 In one study,
87 percent of the patients with accommodative anomalies eliminated
their asthenopia and normalized their accommodative findings after

approximately 26 therapy sessions.26

Therapy to improve AA can result in a concurrent improvement of PFC,
NFV, and stereopsis.109 Vision therapy is the method of choice in
eliminating asthenopic symptoms associated with accommodative
anomalies.110 For those patients who cannot participate in vision
therapy, plus lenses may successfully decrease symptoms.

In a double-blind prospective study to determine the effects of monocular
AA therapy on asthenopia110 the patients in the experimental group had
dramatically improved AA, reduced accommodative time constants, and
significantly reduced symptoms. None of these changes was evident in
the control group. When the control group underwent therapy identical
to that received by the experimental group, a similar reduction in
symptoms and normalization of accommodative function was
achieved.110

These studies demonstrate that vision therapy can alter accommodation,
with a resultant change in the amplitude and facility and a decrease in
symptoms. Therapy can also result in positive changes in the magnitude,
velocity, and gain of the accommodative response.111,112
Accommodative therapy not only eliminates symptoms but is associated
with objective changes in the velocity of the accommodative response
and a concurrent decrease in recorded time constants.112 Therapy
improves the time characteristics, including both latency and velocity, of
the accommodative response.113

42 Accommodative and Vergence Dyxfunction

•

Vergence Therapy.

Fusional vergence therapy improves slow

vergence (vergence adaptation); thus it reduces the apparent
vergence error. This reduction in the residual vergence error
apparently causes a change in the AC/A ratio.114 Other
important functions of slow vergence include maintenance of
fusion following blinking, reduction of the fusional demand with
the onset of presbyopia, and maintenance of binocularity with
the alteration of orbital contents that occurs with age and
diseases such as hyperthyroidism. If the vergence and
accommodative systems are functioning properly when a steady-
state level of accommodation or vergence is reached, the slow
accommodation and vergence systems maintain accommodation
and vergence without effort. The fast and slow vergence and
accommodative systems also use proximal, tonic, and voluntary
vergence and accommodation to reduce their loads. Defects in
any one of these systems alone may not result in asthenopia or
strabismus, owing to overlap with components in other systems.

Numerous studies have evaluated the effectiveness of vergence therapy
in eliminating subjective and objective findings associated with binocular
anomalies.87,115-119 These studies demonstrate that vergence therapy
improves vergence ability, and that the effects persist over time (Table
5). It should be noted that all of the studies demonstrating the efficacy of
vision therapy used in-office therapy regimens.

The Care Process 43

Table 5

Effectiveness of Vision Therapy for Vergence Dysfunction

Research Results

Vergence Dysfunction

Study Authors

Summary/Interpretation

Convergence
insufficiency

Cooper & Duckman17
Grisham54

72% of patients reported cured,
19% reported improved, 9%
reported failed

Grisham, et al115

Vision therapy has a lasting effect
when a complete cure is achieved.

Wick120

Age is not a deterrent to successful
treatment.

Cooper,

al121

Results demonstrated a dramatic
improvement in vergence
amplitudes with a concurrent
decrease in symptoms.

Intermittent exotropia

Coffey, Wick, Cotter, et
al122

Pooled success rates of different
treatment regimens (59% for
vision therapy, 46% for exotropia
surgery, and 28% for passive
therapy [e.g., minus lenses,
occlusion, and/or prisms]) suggest
that vision therapy is more
effective than surgery.

Sanfilippo &
Clahane123

64.5% reported cured, 9.7%
reported improved, 9% reported
fair

Sanfilippo &
Clahane124

Subsequently after 5 years, 52%
remained cured, 32% remained
improved.

Mann125
Durran126
Cooper & Leyman127
Altzier20
Chryssanthau128
Daum129

Similar rates of success for vision
therapy have been reported by
these studies.

44 Accommodative and Vergence Dyxfunction

Table 5 (Continued)

Vergence Dysfunction

Study Authors

Summary/Interpretation

Goldrich130

Highest success rate occurred
when office therapy was
supplemented with home vision
therapy.

Total elimination of symptoms in
80% of patients with the following
improvements: mean divergence
amplitude from 8 PD to 16 PD,
recovery value from 2 PD to 10
PD, and accommodative facility
from 1.5 cpm to 8 cpm.

Convergence excess

Gallaway &
Scheiman131

Vision therapy alone is highly
effective in eliminating abnormal
vergence findings associated with
CE.

Vision therapy is effective with
patients having small vertical
deviations and for older
decompensated vertical deviations.

Vertical deviations

Cooper132
Robertson & Kuhn133

Vision therapy may be used to
decrease prism adaptation and the
need for future increases in prism
correction.

Cooper132

Vision therapy is a better option
for patients with noncomitant
deviations, patients who wish to
wear contact lenses, patients in
whom the size of the vertical
deviation is different at distance
vs. near, and patients who adapt to
prism.

________________________________________________________

Vision therapy for vergence dysfunction has a high success rate. Pooled
data for patients with CI indicate that 72 percent of patients have been
cured, 19 percent improved significantly, and only 9 percent failed.17,54

The Care Process 45

Vision therapy has a lasting effect when a complete cure is achieved.115
Moreover, age is not a deterrent in the successful treatment of binocular
anomalies.120

A controlled, prospective, double blind, A-B reversal study to evaluate
experimental treatment versus placebo treatment for a group of patients
diagnosed with CI used automated therapy with random dot stereograms
in an operant conditioning paradigm to improve vergence amplitudes.
The experimental group had dramatic improvement in vergence
amplitudes and concurrent decrease in symptoms. When the control
group crossed over to become the experimental group, the findings were
similar.121

The pooled success rates of different treatment regimens for intermittent
exotropia have been reported as: 59 percent for vision therapy, 46
percent for surgery, and 28 percent for passive therapy (minus lenses,
occlusion, and/or prisms).122 These data suggest that vision therapy is
more effective than surgery in patients with intermittent exotropia.122

A study evaluating the use of vision therapy in 31 intermittent exotropia
patients reported that 64.5 percent were classified as cured; 9.7 percent,
improved; and 9 percent, fair.123 A followup study found that after 5
years, 52 percent of these patients remained cured, while 32 percent were
in the improved group.124 Similar findings have been reported by other
studies.20,125-129 One study reported that the highest success rate
occurred when office therapy was supplemented with home vision
therapy.130

The latest of recent studies demonstrating the effectiveness of

vision therapy for CE,131 treated 68 patients diagnosed with CE. Total
elimination of symptoms occurred in 80 percent of the patients. Among
the improvements achieved with vision therapy were an increase in mean
divergence amplitude from 8 PD to 16 PD, an increase in recovery value
from 2 PD to 10 PD, and increased accommodative facility from 1.5 to 8
cycles per minute. Prior to therapy, some subjects had spectacles
prescribed to eliminate the esophoria; others did not. When the results
for the patients receiving vision therapy alone were compared with the
results for those patients initially receiving reading spectacles and then

46 Accommodative and Vergence Dyxfunction

undergoing vision therapy, there was no difference in the post-vision
therapy results, suggesting that vision therapy alone is highly effective in
eliminating abnormal vergence findings associated with CE.131

Vertical prism is usually the treatment of choice for vertical deviation.
However, vision therapy has been shown to be effective in a small
sample of patients with vertical deviations and in patients with
longstanding decompensated vertical deviations. Vision therapy may be
used to decrease prism adaptation as well as to reduce the need for future
increases in prism correction.132,133 Vision therapy may be a better
option for a range of patients who have noncomitant deviations, who
wish to wear contact lenses, whose vertical deviation differs in
magnitude at distance and near, and who adapt to prism.132

Patients with closed head injuries often develop accommodative
dysfunction and CI secondary to trauma. Studies comparing therapeutic
options for these patients37,38,134-136 have concluded that patients
with closed head injuries who have associated accommodative and/or
vergence anomalies have a higher success rate with vision therapy than
with surgery and/or lens therapy. However, head-injured patients may
need prisms or surgery to supplement vision therapy treatment.

Lens and Prism Therapy

•

Horizontal Prisms

. Clinicians often prescribe prism to

eliminate symptoms of asthenopia and to reduce the fusional
vergence demand in patients with vergence dysfunction. Two
common methods of determining the amount of prism to
prescribe are (1) to satisfy Sheard's criteria and (2) to eliminate
the FD.137 One study evaluated the effect of prescribing prism
using the associated heterophoria to eliminate the FD in three
groups of patients: symptomatic exophoric patients, symptomatic
esophoric patients, and a control group. All patients were given
two pairs of spectacles to be worn for 2 weeks, one pair with a
prismatic correction that eliminated the associated phoria and the
second pair with no prism. While 73 percent of the symptomatic
exophoric patients and 90 percent of the symptomatic esophoric

The Care Process 47

patients preferred the prismatic glasses, 86 percent of the
asymptomatic patients rejected the prismatic glasses.138

Prism may be the only viable treatment for CI in patients who are unable
to participate in a vision therapy program because of time, cognitive, or
financial constraints. Patients with symptomatic vergence anomalies
may be treated with prisms. Unfortunately, some patients' adaptation to
prismatic correction limits its effectiveness. Slow vergence (prism or
vergence adaptation) varies from patient to patient. It also varies with
the amount of time spent wearing the prism, the power or strength of the
prism, and the direction of prism placement (e.g., base-out, base-up).
When prism adaptation occurs, prism therapy is contraindicated for two
reasons: (1) the prism will not permanently neutralize the deviation, and
(2) strong vergence adaptation will not be able to handle the stress placed
on the vergence system by the heterophoria. Only when there is a
significant deviation with minimal vergence adaptation can prism
compensation be effective.

Adaptation to base-out and base-in prisms differs. As expected, most
people adapt faster and more completely to base-out prism than to base-
in prism.139,140 Prolonged wearing of prisms not only alters the
heterophoria position, but also results in a readjustment of horizontal
fusional amplitudes.140 Once adaptation has occurred, measurements of
the fusional vergence amplitudes, with the prism in place, are almost
identical to the measurements prior to wearing the prism. Most of this
change occurs within the first 15 minutes of wearing the prism.

Vergence adaptation also occurs with noncomitant deviations.141-143
The phenomenon of adaptation, a continuous process that can occur over
the entire oculomotor field, explains why patients who wear incorrectly
centered ophthalmic lenses or anisometropic prescriptions may not
complain. Many patients adapt to a newly introduced prism and its
abrupt removal may result in diplopia and/or asthenopia. Symptomatic
patients who do not adapt to prisms usually report a reduction in
asthenopia once they wear a prism prescription.

•

Vertical Prisms

. Vertical deviations may be divided into three

different categories: small-angle comitant deviations; large-

48 Accommodative and Vergence Dyxfunction

angle, newly acquired paretic deviations; and large-angle,
decompensated, older deviations. Studies have shown that
patients with these deviations differ in their adaptation responses
to vertical prism.139,144 Although the adaptation process varies
from individual to individual, in general, the larger the prism, the
less complete the adaptation process. The longer the prism is
worn, the more complete the adaptation process and the longer
the recovery when the prism is removed. Patients who do not
show significant adaptation may benefit from prism correction.

Clinically, adaptation can be determined by having the patient wear a
vertical prism for as little as 1-2 hours. Adaptation can be predicted to
occur whenever a heterophoria increases dramatically after repeated,
prolonged cover testing.

The effectiveness of prism is limited by torsional deviations,
noncomitancies, and anisometropia. Surgery or vision therapy may be
needed to supplement prismatic correction.

•

Plus Lenses.

The purpose of plus lenses is to decrease the

demand on the accommodation system and/or to reduce the
amount of the esodeviation by manipulating the crosslink AC/A
ratio. Adaptation does seem to play a significant role in the
prescription of plus lenses. The effectiveness is limited in
patients who demonstrate accommodative dysfunction with
asthenopia in the absence of a large heterophoria, and in those
whose accommodative and fusional amplitudes are constricted
but balanced.

•

Minus Lenses.

Minus lenses may be used to change the motor

demand of the vergence system to reduce the amount of
exodeviation.

•

Surgery.

The purpose of extraocular surgery is to decrease the

size of the deviation; therefore, it is rarely indicated for
nonstrabismic binocular vision disorders. One study advocates
surgical intervention for CI when vision therapy fails;145
however, this study did not have a large enough sample to

The Care Process 49

support the author's conclusion concerning the use of surgery as
a primary mode of treatment for CI.

Surgery may be considered in noncomitant vertical deviations which
have a significant torsional component. Newly acquired large-angle
vertical deviations that cannot be resolved within 6 months may require
surgery.24 As a general rule, vision therapy alone is ineffective in
treating newly acquired large-angle vertical deviations. If the patient is
satisfied with prismatic correction or vision therapy, surgical intervention
is not necessary.

2. Available

Treatment

Options

Treatment of accommodative and vergence anomalies is designed to
eliminate signs and symptoms such as headaches, asthenopia, poor
academic performance, poor job performance, loss of concentration, and
ocular and systemic fatigue. Because it also eliminates other symptoms
such as diplopia, reduced stereopsis, and motion sickness, treatment
generally improves the patient's quality of life.

Treatment options can be divided into the following broad categories:
optical correction including added lens power and prism; vision therapy;
pharmaceutical agents; and extraocular muscle surgery. Therapeutic
results can vary due to differences in the application of the specific
treatment regimen.

a. Optical

Correction

•

Ophthalmic lenses.

Appropriate spectacle lens correction of

any existing refractive error is the first consideration in treating
persons with vergence or accommodative anomalies. Plus lenses
are often effective in eliminating symptoms in the patient who
has an accommodative insufficiency or imbalanced positive and
negative relative accommodative values. In addition, plus lenses
may positively affect abnormal esophorias according to the
AC/A ratio.

50 Accommodative and Vergence Dyxfunction

Plus additions at near may be used for patients diagnosed with an
accommodative anomaly, or for those with an abnormally high AC/A
ratio. The lens power may be determined by many different methods:
balancing the PRA and NRA values; cross-cylinder; near point
retinoscopy; or calculation of the AC/A ratio to determine the minimum
lens power that can significantly reduce the near deviation.

•

Prisms.

Prisms are often effective in eliminating vergence

disorders symptoms that involve a significant motor deviation
(tonic vergence anomaly).

Horizontal Prisms -- Sheard's criterion can be used to calculate the
amount of prism required to alleviate symptoms using the following
formula:

prism power = 2 X heterophoria - opposing vergence

Other methods of prescribing prism include using Percival's criterion, in
which the clinician prescribes prism to place Donder's line in the middle
third of the graph in graphical analysis, and FD methods, in which the
clinician prescribes the amount of prism that eliminates the FD (i.e., the
associated phoria).

Vertical Prisms -- There are three types of vertical deviations: (1)
longstanding, asymptomatic deviations that have very strong vergence
adaptation; (2) longstanding deviations that decompensate and have
moderate vergence adaptation; and (3) recent, small deviations with
minimal vergence adaptation. Each of these vertical deviations requires
a different prismatic correction. Patients with old deviations that
decompensate usually present with minimal symptoms in relationship to
the size of the deviation. The prismatic correction needed to eliminate or
reduce symptoms is usually minimal compared with the magnitude of the
deviation. On the other hand, the patient who has a newly acquired
hyperdeviation with minimal vergence adaptation may require full prism
correction, which is defined as the amount of prism needed to correct
either the heterophoria or the recovery value. Patients who have strong

The Care Process 51

vergence adaptation and are asymptomatic usually should not be treated
with prism.

b. Vision

Therapy

Three general phases of vision therapy will be discussed in this section:
accommodation, vergence, and accommodative/vergence interaction.
The first phase of therapy is to normalize accommodative and vergence
amplitudes. Most clinicians use large targets in which convergence and
divergence demand is slowly changed. The patient is encouraged to
exert maximum effort to increase his or her vergence amplitudes.
Accommodative facility exercises are performed concurrently.

The second phase of accommodative and vergence therapy is designed to
increase the speed of response to accommodative and vergence stimuli.
During this phase, it is beneficial to use targets that gradually become
smaller and to use different stimuli to obtain generalization. After the
amplitudes reach normal levels, the patient is encouraged to repeat the
task enough times to make the response become automatic and effortless.
Once monocular accommodative facility has improved, binocular
accommodative facility procedures can be performed. Suppression
controls may be needed with the binocular accommodative techniques.
In general, the power of the binocular accommodative flippers is
increased until the patient can successfully clear +/-2.50 D, according to
a specified criterion.13

The third phase of vision therapy uses jump or step vergence stimuli.
Instead of responding to incrementally increasing stimuli, the patient is
required to make large-jump accommodative and vergence movements.
Finally, accommodation and vergence are integrated through techniques
that stimulate accommodation while holding vergence stable and vice
versa. This final phase of vision therapy is designed to automate both
accommodative and vergence reflexes.

Vision therapy increases the magnitude and the velocity of the fast fusion
system. In addition, there is a concurrent increase in both the magnitude
and velocity of the slow vergence system (vergence adaptation). In a
study to evaluate the effect of vision therapy on vergence adaptation,

52 Accommodative and Vergence Dyxfunction

individuals who underwent 8 weeks of vision therapy that consisted of
push-ups and fusional amplitude therapy had improved vergence
adaptation and fusional amplitudes.144 Subsequent studies have
demonstrated that vision therapy alters the FDC, specifically, flattening
the FDC and concurrently reducing the symptoms.11

The success of vision therapy lies in the improvement of both the
accommodative and vergence adaptation systems because these systems
are the most important for a person's long-term comfort.146 Although
the patient may have a normal fast vergence system, he or she may have
an abnormal slow vergence system, with the resulting symptoms. Thus,
therapy is first aimed at improving reflex-fast fusional vergence, then at
expanding slow vergence responses. In the process, accommodative
flexibility is also restored. The last stage of therapy enhances the
flexibility between accommodation and vergence. The goal of vision
therapy is to re-establish automated, effortless accommodative and
vergence responses under any stimulus condition. Improvement of
amplitudes alone is not sufficient.

There is a paucity of data demonstrating the efficacy of using home-
based vision therapy alone. Home-based vision therapy may be less
effective than in-office therapy because no therapist is available to
correct inappropriate procedures or to motivate the patient. Thus,
preferred clinical management consists of in-office vision therapy
supplemented with home therapy.

Medical (Pharmaceutical) Treatment

Pharmacological agents are of minimal use in the treatment of
accommodative and vergence anomalies, except in the rare case of
myasthenia gravis and CE. With myasthenia gravis, trial use of
Mestinon 60 mg (1-4 times) may be appropriate.

CE patients may

benefit occasionally from the judicious use of phospholine iodine 0.06%
in 2.5% neosynephrine at bedtime.147

Every effort has been made to ensure that the drug dosage recommendations are

accurate at the time of publication of this Guideline. However, because treatment
recommendations change, due to continuing research and clinical experience, clinicians
should verify drug dosage schedules with product information sheets.

The Care Process 53

d. Surgery

Extraocular muscle surgery is rarely advocated to treat nonstrabismic
vergence defects. As a general rule, it should be considered only when
optical correction or vision therapy methods have failed and a significant
heterophoria continues to produce symptoms. There is no surgery
available for accommodative dysfunction.

Management Strategy for Accommodative Dysfunction

a. Accommodative

Insufficiency

The most effective treatment for accommodative dysfunction is vision
therapy to build AA and accommodative facility.112 Therapy should
focus on increasing accommodative amplitudes. Alternatively, plus
lenses may be prescribed at near,148 if the patient is not interested in or
is unable to meet the time requirements for vision therapy.

b. Ill-Sustained

Accommodation

Plus lenses and vision therapy are effective in treating ill-sustained
accommodation.148 Vision therapy is used to improve the speed of the
accommodative response, and generally is the treatment of choice.

c. Accommodative

Infacility

Plus lenses may be prescribed initially, but vision therapy is highly
effective in correcting accommodative infacility.110 The goal of therapy
is to improve the speed and flexibility of accommodation.

Paralysis of Accommodation

The treatment of paralysis of accommodation is directed at determining
its underlying cause and correcting it when necessary. Paralysis of
accommodation may be treated with a progressive addition lens in front
of the affected eye.149 Vision therapy is not effective in treating this
condition.

54 Accommodative and Vergence Dyxfunction

Spasm of Accommodation

The initial treatment of spasm of accommodation consists of plus lenses.
Because, in most cases, lenses alone are not sufficient to eliminate an
accommodative spasm, the clinician should also prescribe vision therapy
to relax accommodation.150 If vision therapy fails, short-term use of a
cycloplegic agent may be prescribed. The ultimate goal is elimination of
the spasm (and the need for cycloplegia and/or plus lenses). In addition
to these treatments, the clinician should reinforce the importance of
visual hygiene in the form of proper working distance, lighting, and
appropriate rest periods.

Management Strategy for Vergence Dysfunction

a. Convergence

Insufficiency

Patients with CI can be treated by various strategies, depending on the
severity of symptoms. Numerous studies have shown that vision therapy
is the treatment of choice for CI (Table 6).26,29,56,57,64,66,120,151-
159 The recommended treatment includes in-office therapy and
supplemental home therapy. Home therapy alone, which is less
effective, may be prescribed when in-office therapy is not possible. To
ensure its success, home therapy should be closely monitored for patient
compliance and to make adjustments when needed. For the patient who
cannot participate in vision therapy, prescribed prisms may reduce the
load on the vergence system; however, prisms do not always alleviate the
patient's symptoms.

The Care Process 55

Table 6

Vision Therapy Success Rate for

Convergence Insufficiency Patients in Large Studiesa

Author

Number

% Cured

% Improved % Failed

Mayou154

Lyle & Jackson151

300

Mann64

142

Cushman & Burri66

Duthie155

123

Mayou153

420b

Mayou153

100

Mellick152

Hirsch57

Passmore & MacLean56

100

Norn29

Hoffman et al26

Wick120

134

Daziel157

100

Pantano158

207

Daum156

110

Cohen & Soden159

28 96

Total 2149

78c

Adapted from Cooper J, Duckman R. Convergence insufficiency: incidence,
diagnosis, and treatment. J Am Optom Assoc 1978; 49:673-80.

The author reported that data were incomplete for 16% of the study population.

Mean weighted cure rate; 2% did not complete orthoptics.

56 Accommodative and Vergence Dyxfunction

b. Divergence

Excess

Among the variety of treatments for DE are occlusion, over-minus
lenses, base-in prism, active vision therapy, and, if necessary, surgery.
Therapy combining diplopia awareness with operant-conditioning
technique to reinforce alignment in the absence of visual cues has been
advocated for DE.18 When active vision therapy is not successful or the
deviation is too large, surgery may improve the outcome. For the
noncommunicative patient, passive therapy that includes part-time
occlusion, base-in prism, and over-minus lenses may be effective.

c. Basic

Exophoria

Most patients with a basic exophoria may be treated like CI patients for
near problems and like DE patients for distance problems. Vision
therapy is usually the initial treatment of choice, and the general goal of
treatment is to improve convergence amplitudes. Therapy usually starts
with near targets; distance targets are added later. Prism treatment is also
an option.

d. Convergence

Excess

Most patients with CE are emmetropic. When hyperopia is present, it
should be corrected. The best treatment options for CE are plus lenses at
near, vision therapy, or both.147 A plus lens addition at near may be
part of the initial treatment for these patients. The prescription can be
determined by calculating the AC/A ratio and prescribing the amount of
plus lens power that significantly reduces or eliminates the near
esophoria. Vision therapy can be successful in meeting its primary goal
to alleviate the symptoms associated with CE. This therapy should
incorporate divergence training and minus lenses. A secondary goal of
therapy for CE is to increase plus lens acceptance to make the spectacle
correction more comfortable and uncover any latent hyperopia, if
present.

The Care Process 57

e. Divergence

Insufficiency

Many patients with DI present with minimal symptoms because they
suppress at distance and have normal binocular vision at near.
Symptomatic patients usually complain of diplopia and asthenopia
during night-time driving, when there are fewer fusion cues. Because
patients with DI usually have low hyperopia or emmetropia and low
AC/A ratios, plus lenses have minimal effect. Prism should be
prescribed for distance only, because wearing the prism at near can cause
asthenopia.

Vision therapy is usually successful in patients with DI. If vision therapy
does not provide the needed therapeutic effect, a prismatic correction at
distance should be considered. Vision therapy may be used in
conjunction with prism correction to decrease the possibility of
adaptation to the prism. When the patient is young, it is important to
differentiate functional DI from acquired DI. Because a sudden-onset DI
in a child is sometimes the first sign of a brain tumor or other serious
neurological condition, the child should have an appropriate neurological
evaluation.

f. Basic

Esophoria

Patients with basic esophoria often have uncorrected hyperopia, and
correcting the hyperopia may eliminate the deviation. If not, prismatic
correction may be prescribed. Generally, the patient should be given the
least amount of prism needed to eliminate all of the symptoms. When
the patient has residual asthenopia or wishes to avoid prismatic
correction, a program of vision therapy may be helpful. The goal is to
eliminate the prism through vergence adaptation, which can be achieved
by increasing the fusional divergence amplitude and decreasing the
prismatic correction by approximately 2 PD every month or so. After the
patient overcomes both the accommodative and vergence deficits for
suppression, he or she should be re-evaluated. If suppression is present,
it should be eliminated.

58 Accommodative and Vergence Dyxfunction

Fusional Vergence Dysfunction

Patients with fusional vergence dysfunction have no significant
heterophoria at distance or near; therefore, lenses and prisms are
generally ineffective. The only treatment for this common binocular
problem is vision therapy focusing on both convergence and divergence
amplitudes. The patient with fusional vergence dysfunction usually has
an abnormal accommodative system, which should also be treated.

h. Vertical

Phorias

Treatment of vertical phorias generally consists of correcting the vertical
deviation with prism. The prism prescribed should be the least required
to eliminate the symptoms. If the symptoms remain, the patient may
have a vergence dysfunction, for which horizontal vergence therapy
should be prescribed.132 The vertical prism may be decreased slowly
over time, concurrent with the extension of horizontal amplitudes.
Vision therapy to increase the ability to control vertical vergence is also
an option, but it is more difficult to train the patient to control vertical
vergence than to control horizontal vergence.160

5. Patient

Education

Patients should be advised that many accommodative and vergence
anomalies are neuromuscular problems and not refractive problems.
Thus, the most effective treatment relies on not only spectacles, but
active vision therapy to eliminate neuromuscular dysfunction. The
patient should also be told that treatment improves accommodative and
vergence reflexes. Proper treatment usually results in a permanent cure,
due to changes in the slow vergence system.

Prognosis and Followup

When the patient is cooperative, the prognosis for the elimination of
accommodative and vergence dysfunction is excellent (see Appendix
Figure 5). The most effective treatment appears to be in-office vision
therapy, supplemented by home therapy. Prisms and lenses may be less
effective in eliminating some vergence dysfunction. The difficulty with

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Schor CM. Fixation disparity and vergence adaptation. In:
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Duke-Elder S. The practice of refraction, 5th ed. St. Louis: CV
Mosby, 1949:141-51.

13.

Cooper J. Accommodative dysfunction. In: Amos JF, ed.
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Allen D, Berman P, Brownson R, Olson D. Analysis of the
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Duane A. A new classification of the motor anomalies of the
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Cooper J, Duckman R. Convergence insufficiency: incidence,
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Cooper J, Medow N. Major review: intermittent exotropia;
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Scheiman M, Wick B. Clinical management of binocular vision:
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Appendix

Figure 5

Frequency and Composition of Evaluation and Management Visits

for Accommodative or Vergence Dysfunction

Dysfunction

Number of

Evaluation

Visits

Treatment

Options

Prognosis

Number of

Follow-up

Visits

(VT)

Management Plan*

Convergence
insufficiency

Vision
therapy;
prisms

Excellent 12-20

Provide in-office VT
with supplement home
VT; use prisms if patient
is not able to participate
in VT; educate patient

Divergence
excess

Vision
therapy;
prism; minus

Good 30

Provide active VT; use
passive VT including
occlusion, base-in prims,
lenses; surgery and minus
lenses for
noncommunicative
patient; surgery if VT is
not successful or the
deviation is too large;
educate patient.

Basic
exophoria

Prism; vision
therapy

Good 30

Treat near problems like
CI; treat distance
problems like DE;
educate patient

Convergence
excess

Plus lenses;
vision
therapy

Excellent 5-25

Prescribe plus lens
addition at near; provide
VT for residual
symptoms; prism;
increase plus acceptance;
use prism for the
nonresponsive patient;
educate patient

Divergence
insufficiency

1-2

Vision
therapy;
prism

Fair 15-25

Differentiate funcational
DI from acquired DI in
children; refer patient for
MRI if neurological; treat
with VT or prismatic
correction at distance;
educate patient

84 Accommodative and Vergence Dyxfunction

Figure 5 (Continued)

Dysfunction

Number of

Evaluation

Visits

Treatment

Options

Prognosis

Number

of Follow

up Visits

(VT)

Management Plan*

Basic esophoria

Prism,
vision
therapy

Good 20

Eliminate deviation by
correcting hyperopia;
prescribe prismatic
correction; provide VT
for residual asthenopia
and to eliminate prism;
educate patient

Fusional
vergence
dysfunction

Vision
therapy

Excellent 15-20

Provide VT balanced
between convergence
and divergence; treat
abnormal
accommodative system;
educate patient

Vertical phorias

1-2

Prism;
vision
therapy

Good 20

Correct vertical deviation
with prism; if vergence
dysfunction, proceed
with horizontal vergence
VT; educate patient

Accommodative
insufficiency

Vision
therapy, plus
lenses

Excellent 10

Provide VT to build
accommodative
amplitudes and
accommodative facility,
prescribe plus lenses at
near; educate patient

Ill-sustained
accommodation

Vision
therapy; plus
lenses

Excellent 10

Treat with VT or plus
lenses; educate patient

Accommodative
infacility

Plus lenses;
vision
therapy

Excellent 10

Improve speed of
accommodation with
plus lenses initially;
proceed with vision
therapy; educate patient

Paralysis of
accommodation

Optical
correction

Poor --

Determine underlying
cause; correct with
progressive lens when
necessary; educate
patient

Spasm of
accommodation

1-2

Plus lenses;
vision
therapy;
cycloplegic
drug

Fair 10

Begin with plus lenses
and VT; if VT fails, use
cycloplegic drug agent
temporarily; educate
patient

Note: VT = vision therapy; MRI = magnetic resonance imaging.
* See Guideline for other management strategies.

Appendix

Figure 6

ICD-9-CM Classification of Accommodative and Vergence

Dysfunction

Presbyopia 367.4

Disorders of accommodation

367.5

Paresis of accommodation

367.51

Cycloplegia

Total or complete internal ophthalmoplegia

367.52

Spasm of accommodation

367.53

Other disorders of refraction and accommodation

367.8

Transient refractive change

367.81

Other 367.89

Drug-induced disorders of refraction and accommodation

Toxic disorders of refraction and accommodation

Unspecified disorder of refraction and accommodation

367.9

Visual disturbances

368

Excludes: electrophysiological disturbances (794.11-794.14)

Subjective visual disturbances

368.1

Subjective visual disturbance, unspecified

368.10

Visual discomfort

368.13

Asthenopia

Photophobia

Eye

strain

Other visual distortions and entoptic phenomena

368.15

Photopsia

Visual

halos

Refractive:
diplopia
polyopia

86 Accommodative and Vergence Dyxfunction

Figure 6 (Continued)

Diplopia 368.2

Double

vision

Other disorders of binocular vision

368.3

Binocular vision disorder, unspecified

368.30

Suppression of binocular vision

368.31

Simultaneous visual perception without fusion 368.32

Fusion with defective stereopsis

368.33

Abnormal retinal correspondence

368.34

Other specified visual disturbances

368.8

Blurred vision NOS

Unspecified visual disturbance

368.9

Heterophoria 378.4

Heterophoria, unspecified

378.40

Esophoria 378.41

Exophoria 378.42

Vertical heterophoria

378.43

Cyclophoria 378.44

Alternating hyperphoria 378.45

Other disorders of binocular eye movements

378.8

Excludes: nystagmus (379.50-379.56)

Palsy of conjugate gaze

378.81

Spasm of conjugate gaze

378.82

Appendix

Figure 6 (Continued)

Convergence insufficiency or palsy

378.83

Convergence excess or spasm

378.84

Anomalies of divergence

378.85

Internuclear ophthalmoplegia

378.86

Other dissociated deviation of eye movements

378.87

Skew

deviation

88 Accommodative and Vergence Dyxfunction

Abbreviations of Commonly Used Terms

Amplitude of accommodation

AC/A

Accommodative convergence/accommodation ratio

ARC

Anomalous retinal correspondence

BI Base-in

BO Base-out

CE Convergence

excess

CI Convergence

insufficiency

CSBV

Clear, single binocular vision

D Diopter

DE Divergence

excess

DI Divergence

insufficiency

FD Fixation

disparity

FDC

Fixation disparity curve

IPD Interpupillary

distance

MEM Monocular

estimated

method

NFV

Negative fusional vergence

NPC

Near point of convergence

NRA

Negative relative accommodation

NRC

Normal retinal correspondence

PD Prism

diopter

PFC

Positive fusional convergence

PRA

Positive relative accommodation

SNR

Spasm of the near reflex

Appendix

Glossary

Accommodation

The ability of the eyes to focus clearly on objects at

various distances.

Accommodative convergence/accommodation (AC/A) ratio

The

convergence response of an individual to a unit stimulus of
accommodation.

Accommodative infacility

Slow or difficult accommodative response to

dioptric change in stimulus; accommodative inertia.

Accommodative insufficiency

Less accommodative amplitude than

expected for the patient's age.

Accommodative vergence

Vergence as a result of accommodation.

Amplitude of accommodation (AA)

The difference between the

farthest point and the nearest point of maximum accommodation denoted
by first sustained blur with respect to the spectacle plane, the entrance
pupil, or some other reference point of the eye, expressed in diopters.

Anomalous retinal correspondence (ARC)

A type of retinal

projection, occurring frequently in strabismus, in which the foveae of the
two eyes do not facilitate a common visual direction; a condition in
which the fovea of one eye has the same functional direction with an
extrafoveal area of the other eye; anomalous correspondence.

Asthenopia

Subjective symptoms or distress arising from use of the

eyes; eyestrain.

Convergence

The turning inward of the primary lines of sight toward

each other.

Convergence excess (CE)

Vergence condition characterized by

orthophoria or near-normal phoria at distance and esophoria at near.

90 Accommodative and Vergence Dyxfunction

Convergence insufficiency (CI)

Vergence condition characterized by

an inability to maintain effortless convergence at near distances. CI is
often accompanied by reduced near point of convergence, exophoria or
exotropia at near greater than the distance measurement, and/or reduced
convergence amplitude in relationship to the demand.

Cover test

A clinical test to determine the ocular alignment of the eyes.

Diplopia

A condition in which a single object is perceived as two rather

than one; double vision.

Divergence excess (DE)

A vergence anomaly characterized by

exotropia or high exophoria at distance greater than the near deviation.

Divergence insufficiency (DI)

A vergence anomaly characterized by

esotropia or high esophoria at distance greater than the near deviation.

Esophoria, basic

Vergence position of the eyes in which the two eyes'

lines of sight cross closer to the patient than the object of regard when
binocular fusion is disrupted, the magnitude of the deviation being the
same at both far and near fixation distances.

Exophoria, basic

Vergence position of the eyes in which the two eyes'

lines of sight cross further than the object of regard when binocular
fusion is disrupted, the magnitude of the deviation being the same at both
far and near fixation distances.

Fixation disparity (FD)

Overconvergence or underconvergence, or

vertical misalignment of the eyes under binocular (both eyes) viewing
conditions small enough in magnitude so that fusion is present.

Fusion

The process by which stimuli seen separately by the two eyes

are combined, synthesized, or integrated into a single perception.

Fusional vergence

Vergence (convergence or divergence) stimulated by

retinal disparity resulting in the avoidance of diplopia. Synonyms:
reflex vergence, disparity vergence.

Appendix

Fusional vergence amplitude

The angle between the maximum

convergence and the maximum divergence of the eyes that can be
elicited in response to change in convergence while the accommodation
response remains constant.

Ill-sustained accommodation

A condition similar to accommodative

insufficiency but lesser in extent.

Near point of convergence (NPC)

The maximum extent the eyes can

be converged.

Negative fusional vergence (NFV)

A measure of fusional convergence

from the phoria position of the eyes to the prism base-in limit of clear,
single binocular vision; fusional divergence.

Negative relative accommodation (NRA)

A measure of the maximum

ability to relax accommodation while maintaining clear, single binocular
vision.

Negative relative convergence

The base-in prism range of clear, single

binocular vision as measured from Donder's line.

Normal retinal correspondence (NRC)

Retinal projection in which the

two foveae (and/or other binocularly paired extrafoveal receptor areas)
have common lines of direction or a common local sign.

Orthophoria

Condition in which, in the absence of an adequate fusion

stimulus, the lines of sight intersect at a given point of reference, usually
the point of binocular fixation; absence of heterophoria.

Orthoptics

The treatment process for the improvement of visual

perception and coordination of the two eyes for efficient and comfortable
binocular vision. Synonyms: vision training, vision therapy.

Paralysis of accommodation

Absence of accommodation due to

paralysis of the ciliary muscle.

92 Accommodative and Vergence Dyxfunction

Positive fusional convergence (PFC)

Fusional convergence measured

in a positive or increasing direction from the phoria position of the eyes
to the base-out prism limit of clear, single binocular vision. Synonym:
positive fusional vergence (PFV).

Positive relative accommodation (PRA)

A measure of the maximum

ability to stimulate accommodation while maintaining clear, single
binocular vision.

Positive relative convergence

The base-out prism range of clear, single

binocular vision as measured from Donder's line.

Proximal convergence

Convergence due to the awareness of nearness.

Synonyms: psychic convergence, voluntary convergence.

Proximal vergence

Convergence response attributed to the awareness

of, or, the impression of nearness of an object of fixation.

Sensory fusion

The ability of the brain to bring together two sensations

with the end result of a single percept.

Spasm of accommodation

A ciliary muscle spasm that produces excess

accommodation.

Stereopsis

The ability to perceive three-dimensional or relative depth

due to retinal disparity.

Tonic vergence

Convergence due to the basic tonicity of the extraocular

muscles, which are responsible, in part, for the distance phoria.

Vergence

The disjunctive movements of the eyes in which the visual

axes move toward each other (convergence) or away from each other
(divergence).

Vergence insufficiency

See convergence or divergence insufficiency.

Version

A conjugate movement in which the two eyes move in the same

direction.