PUPILS, ANTERIOR SEGMENT AND FUNDI

Section 5 of 11

Pupils:

• Pupils of any patient with unexplained visual loss, ptosis or dysmotility should not be dilated until reviewed by the senior examiner for the following reasons:
  • Pupil examination is one of the few objective indicators of potential visual function. The pupils are an important clue to patients with suspected functional visual loss.

  • Horners syndrome is easily missed, unless the combination of anisocoria worse in the dark, pupil dilation lag and ptosis can be correlated.

  • The presence or absence of pupil involvement markedly changes the management of new-onset third nerve palsy.

  • The pupils are clinically normal in myasthenia gravis.

• When recording pupil size, a pupil gauge or millimeter rule should be used with the patient fixating in the distance, in both a dark and illuminated environment.
  • If there is a difference in the size of the pupils (anisocoria) determine if the anisocoria is greater in the dark or in the presence of light.
    • If the anisocoria is less than 1 mm, and remains the same in the light and dark and if the pupils are round and reactive, the patient may have physiologic anisocoria.

    • Anisocoria greater in the dark suggests sympathetic disease such as Horners syndrome.

    • Anisocoria greater in the light suggests parasympathetic disease such as Adies tonic pupil.

  • It should be noted that even if one eye is completely blind, in the absence of iris trauma, the pupil sizes should be equal.

• The briskness of the pupil response should be noted. If the pupils do not react briskly, vermiform constriction, iris notches, and the response to near stimulus should be recorded.
  • The near reaction is best tested with an accommodative target such as a reading card. When testing the near response, do not use an illuminated light source as the accommodative target since the pupillary light response will be added to the near response.
    • If the pupil reacts better to near than with light, light-near dissociation is present. The most common cause of light-near dissociation is probably optic neuropathy.

    • Well known eponymous causes of light-near dissociation include Adies tonic pupil, Parinauds syndrome (dorsal midbrain syndrome), and Argyll Robertson pupil (tertiary syphilis).

• Testing for a relative afferent pupillary defect (RAPD or Marcus Gunn pupil) is an essential part of any eye exam. The designation "relative" afferent pupillary defect is important.
  • Bilateral afferent pupillary defects are common (e.g., optic neuritis patients), but a bilateral relative afferent pupillary defect cannot exist.

  • In a dimly illuminated room, the patient fixates in the distance and a bright light is alternately flashed for 2-3 seconds in each eye.

  • If the light is directed towards one eye and the ipsilateral pupil appears to dilate paradoxically, an RAPD is present.

  • If the light is flashed on one eye and the pupil does not appear to constrict, or there is increased pupillary escape from constriction, an RAPD may also be present.

  • The RAPD can still be tested in patients where one pupil is dilated or unreactive. The examiner examines the pupillary reaction of the undilated pupil while the light is flashed back and forth between the two eyes.

  • In patients with strabismus, direct the light along the pupillary axis of each eye, so as not to induce an RAPD in the deviated eye.

  • Although an RAPD may correspond with ipsilateral poor vision, it is not always the case. For example, macular hole will result in poor acuity, but not result in an RAPD.

  • In patients who have marked unilateral field loss, or unilateral dyschromatopsia, there is usually an ipsilateral RAPD.

  • A lesion confined to the optic tract may cause an incongruous homonymous field defect and a contralateral RAPD.

  • In patients with lesions of the brachium of the superior colliculus, there may be a contralateral RAPD without field loss (midbrain RAPD).

• The differential diagnosis of heterochromia iridum (more commonly known as heterochromia iridis) is vast. Patients with heterochromia iridum may present to the neuro-ophthalmologist with congenital Horners syndrome, Sturge-Weber syndrome, or unilateral glaucoma treated with latanoprost.

• Slit lamp examination is of great utility when the pupil is suspected to be abnormal.
  • Slight irregularities in the shape of the pupil are best seen with the slit lamp. Irregularities in pupil shape may be congenital as with iris coloboma, or acquired as with synechiae (iritis), iris notches (trauma), and iridocorneal endothelial syndrome (glaucoma).

  • In patients with type I neurofibromatosis, Lisch nodules closely resembling iris nevi may be seen on the slit lamp.

  • Purse stringing of the pupil may be seen with Adies tonic pupil; it is best elicited by quickly turning on and off the slit-lamp beam while examining the pupil.

• Pupil-gaze synkinesis is a sign of aberrant regeneration of the third cranial nerve. Most commonly the pupil constricts on adduction. While the patient is fixating in the distance, the size of the pupils in primary gaze to the pupil size on adduction is compared.