The goal of 'The Eye Digest' is to provide objective information to the public about LASIK surgery. Given the extensive publication record and surgical experience, we believe we are qualified to provide you with credible and unbiased information on all aspects of laser vision correction.

In addition to a general overview of LASIK surgery, we are posting review articles written by 'The Eye Digest' editors. These articles are comprehensive peer-reviewed and evidence-based treatise on several issues associated with LASIK.

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Review Articles Published in Professional Journals Laser eye surgery for refractive errors Published in The Lancet. It is the world's leading medical journal. Laser Vision Correction - Preoperative Considerations. Videos

Overview of Laser Vision Correction Surgery - Essential Facts

Several effective options for laser refractive surgery are available. Navigating the complex array of options can be difficult, but more choices also bring the opportunity to meet more of the needs of an individual patient. The choices can broadly be divided into:

• Flap Surgery (Laser-Assisted In Situ Keratomileusis - LASIK)
LASIK is lamellar laser refractive surgery in which the excimer laser ablation is done under a partial-thickness lamellar corneal flap. Until recently, the lamellar flap could only be made with a microkeratome. The microkeratome uses an oscillating blade to cut the corneal flap. A femtosecond laser (Intralase) has now been developed that can etch lamellar flaps within the cornea stroma at a desired corneal depth. The femtosecond laser provides more accuracy in flap thickness than previous methods and it might be more reliable in cases of steep or flat corneas.

Sub-Bowmans keratomileusis (SBK) - A new trend in LASIK. The only differentiating feature of sub-Bowmans keratomileusis is that the corneal flap is much thinner than usual LASIK flaps. Flap thickess in SBK is less than 100 microns. There may be theoretical advantages of SBK like less corneal nerve damage (therefore less dry eye complication). At this point, it is not possible to evaluate the risk-benefit of SBK because of non-availability of high quality published data.

• Surface Surgery (photorefractive keratectomy [PRK], laser epithelial keratomileusis [LASEK], and Epi-LASIK).
In these procedure the excimer laser is used to ablate the most anterior portion of the corneal stroma. These procedures do not require a partial thickness cut into the stroma. Surface ablation methods differ in the way the epithelial layer is handled. In PRK the epithelium is removed, a large epithelial defect ensues, and healing occurs by migration of surrounding epithelium (usually within a week). In LASEK and Epi-LASIK surgery, the patient's epithelium is not removed. The epithelium is lifted as a sheet and then after laser ablation, the epithelial sheet is re-placed to cover the treated area. In LASEK dilute alcohol is used to loosen the epithelium. LASEK procedure was developed by Dr. Dimitri Azar, Editor of The Eye Digest. In Epi-LASIK, a purely mechanical means of epithelial dissection (using Epikeratome) allows the creation of the epithelial sheet.

Compared with surface ablation, LASIK results in earlier and faster improvement of uncorrected visual acuity, and has less (or almost no) postoperative discomfort, improved stability, and predictability. With LASIK, however, the risks of flap-related complications (wrinkles, debris, folds, buttonhole, and diffuse lamellar keratitis) may be associated with the creation of the lamellar flap.

Conventional versus wavefront-guided treatment: Regardless of whether the surgeon does LASIK or surface ablation, there is an additional choice in “how” the laser will be applied to the cornea. Conventional ablations make use of data obtained during manifest and cycloplegic refractions. This data, that is generated by humans (surgeon, technician etc) based on their examination of your eye, is what tells the laser how much to treat and how to treat. The ablation profile will contain a spherical component and an astigmatic component. Conventional ablations essentially treat what glasses have been treating for hundreds of years. Wavefront-guided treatments allow optical properties beyond spherical and cylindrical defocus to be corrected. Wavefront aberrometers (automated machines) capture data that describe the optical aberrations of a patient's eye. This data, that is generated by an automated machine (wavefront aberrometer) based on an average of 3 automated recordings, is what tells the laser how much to treat and how to treat.

Whether the additional information obtained with wavefront-guided treatments is translated into better ablations and improved acuity compared with conventional LASIK can be determined by comparing the FDA trials data. In wavefront-guided LASIK, 89% of patients achieved uncorrected visual acuities of 20/20 or better . By contrast, with conventional treatment, patients reached 20/20 or better only 72% of the time. Therefore more people can expect to achieve uncorrected vision of 20/20 with wavefront-guided LASIK. The likely reason for this difference is that wavefront-guided treatments treat higher order aberrations as well (conventional treatments do not treat higher order aberrations).

Will I have 20/20 vision without glasses after LASIK?
If the myopia is low to moderate (i.e. -7 D or less), then 96% patients achieve uncorrected visual acuities better than 20/40, however only 72% of patients achieve vision equal to or better than 20/20. As mentioned earlier, more people achieve 20/20 vision with wavefront-guided treatment. If the myopia is high (i.e. more than -7 D ), then 89% patients achieve uncorrected visual acuities better than 20/40, however only 48% of patients achieve vision equal to or better than 20/20. Note that the uncorrected vision results in high myopes is not as good as in low myopes (FDA data). LASIK and surface ablation have largely similar vision outcomes. Therefore, most - but not all - people will have 20/20 vision after LASIK without glasses. Some people will not be able to "get rid of glasses" to see 20/20. Taken together, this means that LASIK will almost certainly reduce your dependence on glasses and contact lenses, however, there is no certainty and there can be no guarantee that you will be able to achieve perfect vision without glasses. You have 90 to 95% chance of passing the vision test to get a drivers license without glasses (i.e 20/40 vision) and therefore 90 to 95% chance that you will be able to legally drive without glasses after LASIK. Our recommendation, however, is that you drive with the best vision that your eyes are capable of achieving.

Serious complications from refractive surgery are rare, as evidenced by the low rate of loss of best spectacle-corrected visual acuity. However, before undergoing any refractive procedure, you should carefully weigh the risks and benefits based on your own personal value system, and try to avoid being influenced by friends that have had the procedure or doctors encouraging you to do so. Remember that, even though rare, complications do occur.

• Some patients lose vision. Some patients lose lines of vision on the vision chart that cannot be corrected with glasses, contact lenses, or surgery as a result of treatment. Loss of best spectacle-corrected visual acuity of more than two lines is noted in just under 1·0% of patients (FDA data)
   

• Some patients develop debilitating visual symptoms. Some patients develop glare, halos, and/or double vision that can seriously affect nighttime vision. Even with good vision on the vision chart, some patients do not see as well in situations of low contrast, such as at night or in fog, after treatment as compared to before treatment.
  
  Even though it is unclear to what extent pupil size plays a role in the pathogenesis of glare and halos, patients with pupil diameter of more than 6.0 mm should be informed of the significant risk of night vision disturbances after LASIK. Generally, these symptoms abate over time. It is not clear if this is due to resolution of an underlying anatomic irregularity or to patient's adaptation. A small subset of patients report no significant improvement and can be substantially incapacitated under various lighting situations, such as night driving, despite good uncorrected visual acuity at high contrast levels (during daytime).
  
  There is growing evidence that higher order aberrations are the main reason for glare and halos after LASIK. Another reason relates to the pupil size. These symptoms are more pronounced after treatment of cylindrical errors (for high astigmatism) due to the oval shape of laser treatment with inherently smaller optical zone in the steep meridian. If pupils dilate to a diameter larger than the size of the optical treatment zone, rays of light refracted by the untreated peripheral cornea are not focused at the same position as the central rays and result in blur circles. Glare and halos may be significantly reduced through enlargement of the ablation zone by means of the currently developed wavefront- or topography-guided lasers. Leaving the car dome's light on when driving at night has also been reported to improve symptoms because the pupil becomes smaller.
  

  Starburst Headlights after LASIK Ghosting in Dim Light video from: VisionSimulations
   

• You may be under treated or over treated. Only a certain percent of patients achieve 20/20 vision without glasses or contacts. You may require additional treatment, but additional treatment may not be possible. You may still need glasses or contact lenses after surgery. This may be true even if you only required a very weak prescription before surgery. If you used reading glasses before surgery, you may still need reading glasses after surgery.
  
  Variations in corneal healing, atmospheric pressure, humidity, and ambient temperature are among the many factors that contribute to the relative unpredictability of refractive surgical procedures. Surgical procedures based on inaccurate refractions could result in significant residual or induced postoperative refractive errors. These include erroneous refraction, relying on non-cycloplegic refraction in an accommodating patient, and wrong information input into the laser secondary to human error. Failing to reexamine a contact lens wearer until a stable and reproducible refraction is obtained may result in unexpected refractive outcomes.
  
  Over- or under-correction may be corrected by lifting the flap (even months after the surgery) and applying additional laser ablation.
   

• Some patients may develop severe dry eye syndrome. The dry eye condition after LASIK may be due to decreased corneal sensation, resulting from severing of corneal nerves, with subsequent decreased blinking rate. As a result, your eye may not be able to produce enough tears to keep the eye moist and comfortable. Dry eye not only causes discomfort, but can reduce visual quality due to intermittent blurring and other visual symptoms. This condition may be permanent. Intensive drop therapy and use of plugs or other procedures may be required.
  
  To learn more about Dry Eyes click below

  Dry Eye Info Questionnaire Exam & Tests Treatment Overview Artificial Tears Restasis
  
   

• Results are generally not as good in patients with very large refractive errors of any type. You should discuss your expectations with your doctor and realize that you may still require glasses or contacts after the surgery.
   

• For some farsighted patients, results may diminish with age. If you are farsighted, the level of improved vision you experience after surgery may decrease with age. This can occur if your manifest refraction (a vision exam with lenses before dilating drops) is very different from your cycloplegic refraction (a vision exam with lenses after dilating drops).
   

• Long-term data is not available. LASIK is a relatively new technology. The first laser was approved for LASIK eye surgery in 1998. Therefore, the long-term safety and effectiveness of LASIK surgery is not known.

You are probably NOT a good candidate for refractive surgery if:

• You are not a risk taker. Certain complications are unavoidable in a percentage of patients, and there are no long-term data available for current procedures.

• It will jeopardize your career. Some jobs prohibit certain refractive procedures. Be sure to check with your employer/professional society/military service before undergoing any procedure.

• Cost is an issue. Most medical insurance will not pay for refractive surgery. Although the cost is coming down, it is still significant.

• You required a change in your contact lens or glasses prescription in the past year. This is called refractive instability. Patients who are:

• In their early 20s or younger, 

• Whose hormones are fluctuating due to disease such as diabetes,

• Who are pregnant or breastfeeding, or 

• Who are taking medications that may cause fluctuations in vision, 

are more likely to have refractive instability and should discuss the possible additional risks with their doctor.

• You have a disease or are on medications that may affect wound healing. Certain conditions, such as autoimmune diseases (e.g., lupus, rheumatoid arthritis), immunodeficiency states (e.g., HIV) and diabetes, and some medications (e.g., retinoic acid and steroids) may prevent proper healing after a refractive procedure.

• You actively participate in contact sports. You participate in boxing, wrestling, martial arts or other activities in which blows to the face and eyes are a normal occurrence.

• You are not an adult.  Currently, no lasers are approved for LASIK on persons under the age of 18.

Precautions
The safety and effectiveness of refractive procedures has not been determined in patients with some diseases. Discuss with your doctor if you have a history of any of the following:

Other Risk Factors
Your doctor should screen you for the following conditions or indicators of risk:

• Blepharitis. Inflammation of the eyelids with crusting of the eyelashes, that may increase the risk of infection or inflammation of the cornea after LASIK.
   

• Large pupils. Make sure this evaluation is done in a dark room. Younger patients and patients on certain medications may be prone to having large pupils under dim lighting conditions. This can cause symptoms such as glare, halos, starbursts, and ghost images (double vision) after surgery. In some patients these symptoms may be debilitating. For example, a patient may no longer be able to drive a car at night or in certain weather conditions, such as fog.

• Thin Corneas. Cornea is the transparent covering of the eye that is over the iris (the colored - brown or blue - part of the eye). All laser vision correction procedures change the eye’s focusing power by reshaping the cornea by removing tissue - the higher the refractive error, the greater the amount of tissue removed. Performing a laser vision correction on a cornea that is too thin may result in blinding complications.
  
  Average normal cornea is about 550 microns thick (i.e slightly more than half millimeter). An important safety goal during LASIK procedure is to leave sufficient stromal bed beneath the corneal flap that will prevent destabilization of the corneal structural integrity (i.e. bulging or ectasia). While the minimum stromal bed thickness required to preserve the structural integrity of the cornea is not known with certainty, it is thought to be at least 250 microns, and many surgeons recommend leaving even more - upto 275 or 300 microns (more stromal bed thickness equals greater safety). Given that at least 250 microns of stromal bed should be left untreated to prevent the possibility of postoperative blinding complications (ectasia), and given that the corneal flap is about 160 microns in thickness, only limited extent of treatment is possible in patients with thin corneas if LASIK is to be performed. Therefore, if the cornea is thin (about 500 microns or so), then for safety reasons, surface ablation (Epi-LASIK or LASEK) may be preferable to LASIK.

• Previous refractive surgery (e.g., RK, PRK, LASIK).  Additional refractive surgery may not be recommended.  The decision to have additional refractive surgery must be made in consultation with your doctor after careful consideration of your unique situation.

• Dry Eyes. LASIK surgery tends to aggravate this condition.

Finding the Right Doctor If you are considering refractive surgery, make sure you: Compare. The levels of risk and benefit vary slightly not only from procedure to procedure, but from device to device depending on the manufacturer, and from surgeon to surgeon depending on their level of experience with a particular procedure. Don't base your decision simply on cost and don't settle for the first eye center, doctor, or procedure you investigate. Remember that the decisions you make about your eyes and refractive surgery will affect you for the rest of your life. Be wary of eye centers that advertise, "20/20 vision or your money back" or "package deals." There are never any guarantees in medicine. Read. It is important for you to read the patient handbook provided to your doctor by the manufacturer of the device used to perform the refractive procedure. Your doctor should provide you with this handbook and be willing to discuss his/her outcomes (successes as well as complications) compared to the results of studies outlined in the handbook. Even the best screened patients under the care of most skilled surgeons can experience serious complications. During surgery. Malfunction of a device or other error, such as cutting a flap of cornea through and through instead of making a hinge during LASIK surgery, may lead to discontinuation of the procedure or irreversible damage to the eye. After surgery. Some complications, such as migration of the flap, inflammation or infection, may require another procedure and/or intensive treatment with drops. Even with aggressive therapy, such complications may lead to temporary loss of vision or even irreversible blindness. Under the care of an experienced doctor, carefully screened candidates with reasonable expectations and a clear understanding of the risks and alternatives are likely to be happy with the results of their refractive procedure. Advertising Be cautious about "slick" advertising and/or deals that sound "too good to be true." Remember, they usually are. There is a lot of competition resulting in a great deal of advertising and bidding for your business. Do your homework.

What to Expect Before, During, and After Surgery
What to expect before, during, and after surgery will vary from doctor to doctor and patient to patient.  This section is a compilation of patient information developed by manufacturers and healthcare professionals, but cannot replace the dialogue you should have with your doctor.  Read this information carefully and with the checklist, discuss your expectations with your doctor.

Before Surgery
If you decide to go ahead with LASIK surgery, you will need an initial or baseline evaluation by your eye doctor to determine if you are a good candidate. This is what you need to know to prepare for the exam and what you should expect:

If you wear contact lenses, it is a good idea to stop wearing them before your baseline evaluation and switch to wearing your glasses full-time. Contact lenses change the shape of your cornea for up to several weeks after you have stopped using them depending on the type of contact lenses you wear. Not leaving your contact lenses out long enough for your cornea to assume its natural shape before surgery can have negative consequences. These consequences include inaccurate measurements and a poor surgical plan, resulting in poor vision after surgery. These measurements, which determine how much corneal tissue to remove, may need to be repeated at least a week after your initial evaluation and before surgery to make sure they have not changed, especially if you wear RGP or hard lenses.  If you wear:

• soft contact lenses, you should stop wearing them for 2 weeks before your initial evaluation.

• toric soft lenses or rigid gas permeable (RGP) lenses, you should stop wearing them for at least 3 weeks before your initial evaluation.

• hard lenses, you should stop wearing them for at least 4 weeks before your initial evaluation.

You should tell your doctor:

• about your past and present medical and eye conditions

• about all the medications you are taking, including over-the-counter medications and any medications you may be allergic to

Your doctor should perform a thorough eye exam and discuss:

• whether you are a good candidate

• what the risks, benefits, and alternatives of the surgery are

• what you should expect before, during, and after surgery

• what your responsibilities will be before, during, and after surgery

You should have the opportunity to ask your doctor questions during this discussion.  Give yourself plenty of time to think about the risk/benefit discussion, to review any informational literature provided by your doctor, and to have any additional questions answered by your doctor before deciding to go through with surgery and before signing the informed consent form.

You should not feel pressured by your doctor, family, friends, or anyone else to make a decision about having surgery. Carefully consider the pros and cons.

The day before surgery, you should stop using:

• creams

• lotions

• makeup

• perfumes

These products as well as debris along the eyelashes may increase the risk of infection during and after surgery. Your doctor may ask you to scrub your eyelashes for a period of time before surgery to get rid of residues and debris along the lashes.

Also before surgery, arrange for transportation to and from your surgery and your first follow-up visit. On the day of surgery, your doctor may give you some medicine to make you relax. Because this medicine impairs your ability to drive and because your vision may be blurry, even if you don't drive make sure someone can bring you home after surgery.

During Surgery
The surgery should take less than 30 minutes. You will lie on your back in a reclining chair in an exam room containing the laser system. The laser system includes a large machine with a microscope attached to it and a computer screen.

A numbing drop will be placed in your eye, the area around your eye will be cleaned, and an instrument called a lid speculum will be used to hold your eyelids open. A ring will be placed on your eye and very high pressures will be applied to create suction to the cornea. Your vision will dim while the suction ring is on and you may feel the pressure and experience some discomfort during this part of the procedure. The microkeratome, a cutting instrument, is attached to the suction ring. Your doctor will use the blade of the microkeratome to cut a flap in your cornea.

The microkeratome and the suction ring are then removed. You will be able to see, but you will experience fluctuating degrees of blurred vision during the rest of the procedure. The doctor will then lift the flap and fold it back on its hinge, and dry the exposed tissue.

The laser will be positioned over your eye and you will be asked to stare at a light. This is not the laser used to remove tissue from the cornea. This light is to help you keep your eye fixed on one spot once the laser comes on. NOTE: If you cannot stare at a fixed object for at least 60 seconds, you may not be a good candidate for this surgery.

When your eye is in the correct position, your doctor will start the laser. At this point in the surgery, you may become aware of new sounds and smells. The pulse of the laser makes a ticking sound. As the laser removes corneal tissue, some people have reported a smell similar to burning hair. A computer controls the amount of laser energy delivered to your eye. Before the start of surgery, your doctor will have programmed the computer to vaporize a particular amount of tissue based on the measurements taken at your initial evaluation. After the pulses of laser energy vaporize the corneal tissue, the flap is put back into position.

A shield should be placed over your eye at the end of the procedure as protection, since no stitches are used to hold the flap in place. It is important for you to wear this shield to prevent you from rubbing your eye and putting pressure on your eye while you sleep, and to protect your eye from accidentally being hit or poked until the flap has healed.

 

After Surgery
Immediately after the procedure, your eye may burn, itch, or feel like there is something in it. You may experience some discomfort, or in some cases, mild pain and your doctor may suggest you take a mild pain reliever. Both your eyes may tear or water. Your vision will probably be hazy or blurry. You will instinctively want to rub your eye, but don't! Rubbing your eye could dislodge the flap, requiring further treatment. In addition, you may experience sensitivity to light, glare, starbursts or haloes around lights, or the whites of your eye may look red or bloodshot. These symptoms should improve considerably within the first few days after surgery. You should plan on taking a few days off from work until these symptoms subside. You should contact your doctor immediately and not wait for your scheduled visit, if you experience severe pain, or if your vision or other symptoms get worse instead of better.

You should see your doctor within the first 24 to 48 hours after surgery and at regular intervals after that for at least the first six months. At the first postoperative visit, your doctor will remove the eye shield, test your vision, and examine your eye. Your doctor may give you one or more types of eye drops to take at home to help prevent infection and/or inflammation. You may also be advised to use artificial tears to help lubricate the eye. Do not resume wearing a contact lens in the operated eye, even if your vision is blurry.

You should wait one to three days following surgery before beginning any non-contact sports, depending on the amount of activity required, how you feel, and your doctor's instructions.

To help prevent infection, you may need to wait for up to two weeks after surgery or until your doctor advises you otherwise before using lotions, creams, or make-up around the eye. Your doctor may advise you to continue scrubbing your eyelashes for a period of time after surgery. You should also avoid swimming and using hot tubs or whirlpools for 1-2 months.

Strenuous contact sports such as boxing, football, karate, etc. should not be attempted for at least four weeks after surgery. It is important to protect your eyes from anything that might get in them and from being hit or bumped.

During the first few months after surgery, your vision may fluctuate.

• It may take up to three to six months for your vision to stabilize after surgery.

• Glare, haloes, difficulty driving at night, and other visual symptoms may also persist during this stabilization period. If further correction or enhancement is necessary, you should wait until your eye measurements are consistent for two consecutive visits at least 3 months apart before re-operation.

• It is important to realize that although distance vision may improve after re-operation, it is unlikely that other visual symptoms such as glare or haloes will improve.

• It is also important to note that no laser company has presented enough evidence for the FDA to make conclusions about the safety or effectiveness of enhancement surgery.

Contact your eye doctor immediately, if you develop any new, unusual or worsening symptoms at any point after surgery. Such symptoms could signal a problem that, if not treated early enough, may lead to a loss of vision.

REFERENCES:
The above article is based on excerpts from the following published papers in which the editors of The Eye Digest were senior/corresponding authors. The full text of these papers can be accessed from the respective journals. We are providing a journal link that will aid you in finding the full text.

Sakimoto T, Rosenblatt MI, Azar DT. Laser eye surgery for refractive errors
Lancet 2006 Apr 29;367(9520):1432-47.

Melki SA, Azar DT. LASIK complications: etiology, management, and prevention.
Surv Ophthalmol. 2001 Sep-Oct;46(2):95-116.

Sippel KC, Jain S, Azar DT. Monovision achieved with excimer laser refractive surgery.
Int Ophthalmol Clin. 2001 Spring;41(2):91-101.

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