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LASIK Laser Eye Surgery Frequently Asked Questions
Provided by Dr. Gary Kawesch


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What if LASIK is not the best procedure for me?


During your examination, we gather important information regarding the health of your eye, including various measurements regarding your prescription, your pupil size and the shape and thickness of your cornea. Our goal is to help you select the procedure which will have the highest chance of getting you to your goal of clear vision without glasses, while at the same time having the least risk possible of any complications.

Some patients have corneas that are thinner than average, and, depending on the amount of correction needed in these cases, a LASIK procedure could be riskier than in a patient with a cornea of normal thickness. With LASIK, a flap is created and lifted aside, and the laser is used to sculpt the exposed corneal bed, which is usually 130-180 microns deeper into the cornea from the surface.

The laser sculpts the cornea by vaporizing corneal tissue. So, the laser will make the cornea thinner than it was. If the thickness of the corneal bed is reduced too much with LASIK, a complication known as "ectasia" can occur, which is a destabilization of the cornea, causing high levels of nearsightedness, astigmatism and possibly cornea irregular curvatures to result. This is something which needs to be avoided. The amount of corneal tissue vaporized with the laser depends on the degree of correction being attempted, and the treatment zone diameter programmed into the laser. Bigger treatment zones are helpful in reducing nighttime side effects, but they do go deeper into the cornea.

Patients with thinner corneas might be better off with a procedure other than LASIK. A procedure which does not create a flap would give us more cornea to work with, to enable a more complete correction and/or a bigger treatment zone diameter. There are surface treatments available, known as LASEK or PRK. These techniques are extremely similar. They involve removing the very surface layer of the cornea, known as epithelium (usually about 50 microns thick), then lasering the exposed corneal bed. This way, the laser is not vaporizing tissue as deep in the cornea as with LASIK, and the risk of ectasia is lowered. With LASEK, a form of alcohol is applied to the cornea, which loosens (and kills) the surface epithelium. After the laser part of the procedure, the layer of dead and dying epithelial cells is replaced over the treated area to act as a bandage, and a contact lens is placed over that. Much of the healing involves the regeneration of new epithelium cells, over the course of a week. With PRK, no alcohol is used, and the surface epithelial cells are removed with a soft brush. After the laser treatment, as with LASEK, a disposable contact lens is placed on the eye, without replacing the damaged epithelial cells. New epithelium regenerates naturally, over two to three days. Both techniques are effective, however I have found that the alcohol used with LASEK causes significant inflammation and delayed recovery of vision. In other words, patients seem to see and recover more quickly with PRK, without trying to salvage the surface epithelium cells.


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Can I wear contact lenses after surgery if I want to?


It is very uncommon that someone would want or need to wear contacts after surgery. Most patients do not need any correction, and those who do usually just need part-time correction for things like night driving. Rarely will someone want to wear contacts versus glasses for activities like this. If full-time glasses or contacts is needed after surgery, usually a retreatment can be done to improve the vision and reduce the need for use of glasses. In the rare case that someone wants to wear contacts after surgery, usually they can without any trouble (assuring they could wear contacts prior to surgery). There is always the outside possibility that a contact would not fit well, but this is rare.


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What causes nighttime side effects? And what can be done to help it they occur?


Nighttime side effects include blurring at night, glare, and starburst and halos around lights. There are several things that can cause these effects. Residual nearsightedness, farsightedness, and astigmatism can cause these problems. If this is the case, glasses at night, or more surgery may help.

Another possible cause has to do with the size of the pupil and the shape of the treated cornea. In low light, the pupil inside the eye dilates to allow more light into the eye. When the pupil dilates, the light coming into the eye is focused by a larger area of the cornea than when the pupil is small. If light is being focused by more peripheral areas of the cornea that have not been reshaped by the laser, optical aberrations can cause these night effects. The best bet is to reduce the risk of this occurring by using a laser which can reshape a large area of cornea, or to avoid treating patients with very large pupils if a large treatment zone cannot be done.


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What if these effects occur? What can be done?


There are medication eyedrops that can be used to constrict the pupil at night. These will reduce glare, starburst and halos, but they will also cause less light to be allowed into the eye, usually giving murky or washed out night vision. One problem is traded for another, and usually this is not a viable solution. In some patients, though, it may be helpful. Similarly, some patients find that turning on the light inside the car causes just enough pupillary constriction to eliminate annoying night effects.

Treatments which are not centered properly over the cornea can also lead to severe nighttime side effects. This is usually easily avoided by a skilled surgeon. This trouble, if it occurs, is extremely difficult to fix. Future techniques like custom corneal sculpting (custom LASIK) may be the best solution.


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How long will the results of surgery last?


LASIK has been done since 1991, with generally stable results. Beyond this length of time, we do not know. It is important to realize that your eyes still can change as you age, causing a need for glasses or contacts. Some people may become nearsighted or farsighted again over time, though most seem not to. If your eyes are very unstable (i.e. still changing rapidly) prior to surgery, this may continue after surgery. You may decide to wait until your eyes are more stable to have the surgery, if this is the case. If there are changes down the road after you do have LASIK, it is usually easy to have more surgery to adjust the vision. In some cases, this will not be an option.

We do know that as people reach their early 40's they develop presbyopia, and begin to need reading glasses.


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What keeps the flap in position?


There are several things occurring that keep the flap in position without stitches. Initially, there is a vacuum effect created by the cells lining the inner surface of the cornea. These cells, known as endothelial cells, function as a pump to move fluid (water) from within the substance of the cornea into the inner part of the eye. This suction type of force initially holds the flap in position. As the eye heals over the first day or two, the outer surface of the cornea, known as the epithelium, seals the edges of the flap. Over weeks to months, natural substances in the cornea help bond the flap to the underlying cornea.


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Can I lose my corneal flap?


With a flap there is a hinge, which attaches the flap to the rest of the cornea. There is no chance of losing a corneal flap. A corneal flap can be DISPLACED if the eye is rubbed shortly after surgery. This would require repositioning of the flap in the operating room. Rarely (roughly 1 in 1,500 cases), there will be no hinge and the microkeratome will cut a free cap. A free cap CAN be lost, if you rub your eye too hard shortly after surgery. If a free cap is created at the time of surgery, the laser part of the procedure will be done, the cap will be replaced on the eye, and you will be notified of this occurrence so that you can be sure to take extra precautions in the postoperative healing period to reduce the risk of losing the free cap. Please note that, as recently as 1994, this type of surgery was done without any hinge-ALL cases had free caps. It was extremely rare for any of these patients, in those days, to lose their corneal cap.

Even if the corneal cap were to be lost, this would probably not be as disastrous as it sounds. The cornea would overall be somewhat thinner, and there would be a chance of scarring, but overall the vision would likely be quite good. It is possible, but unlikely, that a corneal transplant would be needed. Nevertheless, this is a complication we wish to avoid.


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One Eye or Two at a Time?


Ultimately this choice is up to you, the patient. There are theoretical advantages and disadvantages each way. Basically, two issues arise. One, is there a MORE ACCURATE RESULT when the eyes are done separately? In other words, do we learn something from the outcome of the first eye which we can apply to the second eye to increase the chance of a perfect result? And secondly, is it SAFER to do the eyes separately?

In answering the first question regarding accuracy, a study done at Emory University in Atlanta a few years ago demonstrated NO increase in accuracy if the eyes are done separately. Each eye can respond slightly differently, and any over or undercorrection in the first eye does not predict a similar response in the second eye.

With regard to the second question concerning safety, what we are worried about is a complication occurring which is not apparent at the time of the surgery, but which appears a few hours or days later, and which can occur in both eyes at once if both eyes were treated. An infection is one such complication. If an infection occurs, it usually will occur within the first two or so days postoperatively. An infection in both eyes, if severe, can lead to scarring, loss of vision, and even a need for a corneal transplant. Obviously, this is a situation we wish to avoid. Fortunately, the risk of an infection occurring in even just one eye is remote, but not zero. The risk is on the order of one in 5,000 to one in 10,000 cases. Additionally, most (but not all) infections are treatable and do not cause visually significant scarring. An analogy can be made with contact lenses. Contact lenses can cause corneal infections, scarring and loss of vision, especially extended wear contacts. The risk is fairly low. People generally wear contact lenses in both eyes, and they do take an extremely small risk of getting infections in both eyes at once, which can cause some loss of vision. They take this risk because it is astronomically small.

The advantage of doing both eyes at once is several fold. First, you will only be taking the medications used before, during, and after surgery just once. Any medication has some degree of risk of side effects and, generally speaking, if we can minimize your use of medications, that is beneficial. A second advantage is minimizing the number of office visits necessary for surgery and follow up care. This is certainly a convenience issue, and bear in mind that the decision to have one eye at a time or both at once should not be made simply out of convenience. There may be more to minimizing visits than simply convenience. A statistical analysis of risk presented in 1999 at one of our annual eye surgery meetings showed a higher risk of being injured or killed in a car accident while traveling to or from the doctor's office than risk of loss of vision in both eyes from infection caused by surgery. The point here is that there is risk inherent in almost anything we do. If the risk is acceptably small, then it makes sense to accept that risk. Most of our patients choose to have both eyes treated at once and I, as a surgeon, am very comfortable with that. Some of my patients elect to do the two eyes separately, and that is perfectly acceptable. Ultimately, it is up to each person to decide which way they would like to have the surgery done.


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What is the percentage chance of certain complications occurring?


Various complications have different risk frequencies associated with them. Below is a list of certain complications and their corresponding risk frequencies.


Free corneal cap - 1 case in 1,500 (note: a free cap does NOT mean a lost cap)

Thin, short or irregular flap - 1 case in 1,000. If this occurs, the proper way to proceed is to stop the surgery and NOT perform any laser treatment. The flap is replaced into position, the eye is allowed to heal and the surgery is repeated a few months later. Proceeding with the laser part of the treatment in a case where the flap is not of perfect quality can lead to disastrous results.

Epithelial ingrowth - 1 case in 300. This occurs when the surface layer of the corneal flap, composed of cells called epithelium, sneak under the edge of the flap and grow in the interface underneath the flap. They are normal cells growing in a place they shouldn't be. Treatment is observation if mild and, for more severe cases, surgically lifting the flap, removing the cells, and replacing the flap.

Diffuse interface inflammation (a.k.a. "Sands of the Sahara") - 1 case in 500-1,000. This is an inflammatory reaction in the interface, underneath the flap, which typically occurs one to three days postop. It can cause blurring, redness, and discomfort. It is NOT an infection. Cause is unknown, and treatment is with frequent use of steroid eyedrops. Most cases resolve without incident. Severe cases, which are even more rare, can cause corneal scarring.

Irregular astigmatism - 3 cases in 1,000, for average levels of correction. May increase to 3 cases in 100 for very high levels of correction (above 9 diopters). This is an irregularity in the curvature of the cornea which can cause blurriness. This blurring can NOT be corrected with glasses, or with current laser technology. It nearly always CAN be corrected with a contact lens, and hopefully with future laser technologies like "custom-LASIK." The blurring is usually, but not always, subtle. Most patients with irregular astigmatism still see 20/40 or better in the eye with the irregularity. The irregularities in curvature are microscopic, and can occur even in perfectly executed surgery. The risk of irregular astigmatism increases with novice surgeons, and can be increased with improperly assembled equipment, microkeratome blade irregularities, reused microkeratome blades, improperly calibrated lasers, poorly centered treatments, and generally poor surgical technique.

Flap wrinkles or striations - 1 case in 1,000. Can cause irregular astigmatism. Poor surgical technique can increase the chance of this occurring. Can occur if flap is not repositioned properly at the time of surgery, or can occur if you rub your eye too hard during the initial healing period (first few weeks to one month). Treatment is to lift the flap, smooth out, and reposition. This is usually done only if the striations are affecting the vision. It is possible to have wrinkles or striations which are not affecting vision -- these are best left alone.

Dry eye - Unclear what the exact risk is. The majority of patients do experience dryness after LASIK, which tends to resolve in most but not all patients over several weeks to months. I estimate the risk of permanently drier eyes to be in the 5% range. Treatment is with artificial teardrops. Risk is lower with a nasel flap compared to a superior hinge.

Glare, halos and starburst - Risk depends on many factors, but overall estimate is 5-10%. As with dryness, most patients experience these nighttime side effects and they tend to resolve in most but not all patients over a period of weeks to months. In some cases, they can continue to improve over a year postoperatively. The risk of these side effects depends on the amount of correction being done (larger corrections have higher risk), pupil size (larger pupils have higher risk), treatment zone size used (smaller treatment zone diameters have higher risk), surgeon skill in centering the treatment (better centered treatments will have less risk), and patient cooperation (it seems that patients who focus on the light better tend to have less risk). Most patients who experience permanent increase in nighttime side effects report them as mild, and usually are not impaired by the side effects.


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What is Wavefront Guided LASIK?


Wavefront Guided LASIK s a variation of LASIK surgery which uses "wavefront" technology to custom sculpt the cornea to correct vision. Wavefront Guided LASIK may, in certain situations, provide better results than traditional LASIK.


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What is wavefront technology?


Over the last few years, much research has been done in the area of "adaptive optics," which is the technique of removing blurring in images caused by distortions in optical systems. The field of astronomy has benefited greatly in this manner-new telescopes use microscopically adjusting mirrors and lenses to compensate for optical irregularities, enhancing the quality of the image received.

Ophthalmologists have looked at using this technology to improve laser vision correction techniques. The eye is basically an optical system with lenses (the cornea and the actual lens inside the eye both function as lenses).

Wavefront technology measures optical aberrations or distortions in the eye's optical system, and mathematically describes and quantifies these aberrations. Linking this information to a small-spot scanning laser like the LADARVision allows us to custom-sculpt the cornea and potentially correct these distortions.


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How are the aberrations described mathematically?


Zernike polynomials are mathematical descriptions of aberrations in vision. There are different "orders" or levels of polynomials. The low-level polynomials describe nearsightedness, farsightedness, and astigmatism, which are aberrations easily treated with glasses, or with traditional LASIK.

Higher-order polynomials are more recently described aberrations which affect vision, like coma, trefoil and spherical aberration. There are over a dozen higher-order aberrations--this chart graphically depicts some of the more common higher-order aberrations. Wavefront Guided LASIK or wavefront-based LASIK can treat higher-order aberrations.


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What is the regulatory status of Wavefront Guided LASIK?


The FDA Ophthalmic Devices Panel unanimously recommended approval for the Alcon LADARVision Custom Cornea wavefront-guided laser vision correction system in October of 2002. It is currently F.D.A. approved. The approval is for myopia between 0 and -7 diopters with 0.5 diopters or less of astigmatism. Alcon is the first laser manufacturer to gain approval for this technology.


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Who is a candidate for Wavefront Guided LASIK?


There are two general groups of patients who may benefit from this technology. First, any patient looking for LASIK who is in the proper range of correction, who wants to benefit from the correction of these optical aberrations, may be a candidate. There is evidence that shows Wavefront Guided LASIK treatments deliver sharper postop vision and fewer nighttime side effects than traditional LASIK. Amount of correction, corneal thickness, and general eye health are factors taken into consideration when planning treatment.

A second group of patients who may benefit tremendously from this technology are those who have already had LASIK, PRK, LASEK, or other refractive surgeries and are having some troubles. Problems such as nighttime glare, halos, quality of vision issues, and even simply residual refractive error may be eliminated with Wavefront Guided LASIK. Factors like corneal thickness and general eye health are important in determining candidacy.


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Why is Wavefront Guided LASIK more expensive?


The equipment needed to measure and describe higher order optical aberrations (the wavefront measuring device) is expensive.

Additionally, the laser manufacturer imposes additional royalties for the use of the technology in performing Wavefront Guided LASIK.


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What are the latest results with Wavefront Guided LASIK?


CustomCornea wavefront-guided LASIK using the Alcon LADARVision4000 laser and the LADARWave system is now approved for use. The latest FDA data shows that wavefront-guided treatments using this system provide superior visual results compared to traditional LASIK treatments.

In the latest study, 141 eyes were treated and postoperatively, 63% saw 20/16 or better without glasses. 88% saw 20/20 or better. This data is with a single surgery, without any retreatments (enhancements).

Looking at eyes with no astigmatism (45 eyes), results are even better, with 71% seeing 20/16 or better and 93% seeing 20/20 or better.

Accuracy of corrections was also extremely impressive, with 90% of eyes ending up within 0.5 diopter of the intended correction.

Regarding night vision, only 1.4% of patients reported significant worsening of night vision; nearly ten times more patients (11.3%) reported significant improvement of their night vision after treatment!


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What are the long-term results with Wavefront Guided LASIK?


Since it is so new, we do not have long term data on the results. We don't know if higher-order optical aberrations change as people grow older, or if they remain stable. We do have a 10+ year history with traditional LASIK, and anticipate custom LASIK will provide equally good, if not better long term results.


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Who is NOT a candidate for Wavefront Guided LASIK?


Patients with corneas that are too thin may not be able to have Wavefront Guided LASIK. Some patients may not see much of a benefit from this technology compared to traditional LASIK. Part of our job is to help determine as best we can who would benefit the most from this technology, and recommend it strongly to those patients.


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If I choose to have monovision, does that mean I will never need reading glasses?


No. Presbyopia continues to worsen as you get older, whether or not you have monovision. At some point, the presbyopia may be so bad that reading glasses will be necessary. Still, there is a benefit to having the monovision in that there won't be a complete dependence on glasses for things up close. Larger print will still be readable without glasses, and things slightly farther away (like computers and dashboards of cars) will still be readable. Without monovision, even these things would be blurry without reading glasses. For this reason, patients usually don't "give up" their monovision as they get older. They still read better with the monovision than they would if both eyes are corrected for distance, even though for certain things, reading glasses become necessary.


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What will the vision be in my reading eye with monovision?


The distance vision in the eye set for reading will be less than 20/20. The reading eye is left slightly near sighted to allow for better close vision. The amount of residual nearsightedness may be different for different patients, depending on age at the time of surgery, how "good" the patient wants the reading to be, how much distance vision they are willing to give up, and how long they want to be able to read before they eventually need reading glasses. Typically, the amount of nearsightedness left will be between -1.00 and -2.00 diopters. On average it is -1.50 diopters. Regardless of how many residual diopters of nearsightedness are left to allow for the monovision, the vision on the eyechart can NOT be predicted just by looking at this number. There is no conversion between diopters and visual acuity on the eyechart (20/20, 20/30, etc.). In other words, if you are left with -1.50 diopters of residual nearsightedness you may see 20/40 with that eye in the distance, or you may see 20/100, 20/80 or 20/50. We cannot predict. It can be and is different for different people. In any case, it is not really important WHAT the distance vision is in the reading eye. What IS important is that with both eyes open you are able to comfortably see both near and far for most of your needs.


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I tried monovision with contacts and didn't like it. Will it work better with surgery?


It may, and it may not. Part of it depends on how it was tried with the contact lenses. Was it tried for a day, or for a month or more? Sometimes it takes awhile for the brain to "adjust" to this way of seeing. Were the contact lenses properly fit? Was the proper eye set for distance? Was there any astigmatism that needed to be corrected that wasn't with the contacts? Even if everything was done "right" there is certainly a chance that monovision didn't work well. Some of these people have gone on to have surgery, and have tried monovision with surgery and have liked it. Some still did not like it, even with surgery. There may be some contact lens problems that people attribute to monovision problems, and that is why some people may do well with it, even if the contacts didn't work well.

In a random sample of patients who have done monovision with surgery, 85% of patients end up liking the monovision enough to keep it. 15% decided to give it up and have the reading eye set for distance. These 15% of patients either disliked the monovision, or felt the advantage of some reading ability was not worth the distance tradeoffs.

Patients who tried monovision properly with contacts and didn't like it will have a higher than 15% chance that the monovision with surgery will not be acceptable. It may be a 50:50, or even 80:20 chance that it won't work with surgery. However, if you are strongly motivated to get monovision to work for you, you may still want to try monovision with surgery, even if it did not work with contacts.


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How do you decide which eye to do for distance and which for near?


There are several factors involved. One is, which is the dominant eye? Usually, but not always, the dominant eye is set for distance. Sometimes a patient will come in who has been wearing contacts for monovision and the dominant eye is set for near. If this has been done for awhile, and the patient is doing well with the monovision, we will keep it this way and correct the non-dominant eye for distance. Some patients have a large difference between the measurements in the two eyes. One eye may be -4.00 diopters and the other may be -8.00. Even if the -8.00 diopter eye is the dominant eye, we might make that the reading eye in order to minimize the amount of treatment each eye gets. Part of the purpose of the comprehensive eye exam is to look at all of these issues and decide what will work out best.


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How will monovision impact my ability to perform in certain sports?


It depends on the person and the sport. Fast moving sports may be more affected than slower sports. Racquetball, tennis, baseball, motorcycle racing, and other fast moving activities may be more difficult with monovision because the depth perception might be affected slightly. Slower sports like golf, basketball, skiing and bicycling may be less affected, though some people may notice troubles with these sports with monovision. Everyone is different.

If you choose to do monovision and have problems with certain activities, the options would be to either have a retreatment, give up the monovision and improve this distance vision, or wear a contact lens in the undercorrected eye to bring the two eyes into balance. Many patients who do this for a few hours per week while playing tennis or racquetball, then take the lens out and enjoy the reading advantage monovision offers.


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Gary Kawesch, MD
Laser Eye Center of Silicon Valley

Office Address:

606 Saratoga Ave
San Jose, CA 95129
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