Vision Correction via LASIK

I AM NOT A DOCTOR. THE CONTENTS OF THIS SITE DO NOT CONSTITUTE MEDICAL ADVICE OR OPINION, AND NO WARRANTIES OF ANY KIND ARE OFFERED FOR THE INFORMATION HEREIN. THIS SITE IS OFFERED TO THE PUBLIC FOR EDUCATIONAL PURPOSES ONLY. IF YOU INTEND TO UNDERGO REFRACTIVE SURGERY, YOU ARE STRONGLY URGED TO SEEK THE ADVICE OF A QUALIFIED EYECARE PROFESSIONAL.

I HOLD NO STOCK IN ANY REFRACTIVE SURGERY CONCERN, SAVE PERHAPS BY BEING A SHAREHOLDER IN A FEW DIVERSIFIED MUTUAL FUNDS. I HAVE NO DIRECT FINANCIAL STAKE IN REFRACTIVE SURGERY, AND RECEIVE NO REMUNERATION FOR THIS SITE, WHICH WAS CREATED AND IS PLACED HERE AT MY OWN EXPENSE AS A PUBLIC SERVICE.

—Chris BeHanna

(Note: This site needs some more updating, regarding the status of refractive surgery with the U.S. military, regarding the current state of the art vis-a-vis lasers and topography, regarding the state of the art in the U.S., and regarding a very serious LASIK complication known as Sands of the Sahara, which appears to be caused by improper sterilization of the microkeratome between the end of one surgical day and the beginning of the next. To be absolutely up-to-date, you should follow the newsgroup sci.med.vision. Posts are archived at DejaNews.)

Contents:

• What is LASIK?
• Types of Lasers and Their Limitations
• Topolink and Custom Ablations
• LASIK and Mild Myopia
• Obsolete Methods
• LASIK vs. PRK
• My Personal Experience
• What You Experience During LASIK
• A Note to Pilots and Military Candidates
• Links to Detailed Technical Information

What is LASIK?

LASIK stands for “laser-assisted intrastromal in-situ keratomileusis,” a vision correction procedure in which a flap of 160-180 microns depth is cut in the front of the cornea, the flap is folded back to expose the stroma of the cornea, an excimer laser ablates (reshapes) the exposed stroma, and the flap is folded back down. The anterior layers of the cornea (epithelium, Bowman’s Layer) are preserved (unlike in PRK, in which Bowman’s Layer is burned away by the laser and does not grow back), and there is much less post-operative pain than with PRK, as well as lower incidence of dry eyes, hazing, and scarring. Healing time is much faster than for RK or PRK, and patients can see right away (I was seeing 20/25 the very next day, and 20/20 a couple of days later). The surgery corrects myopia, hyperopia, and astigmatism, but cannot fix presbyopia. If you needed reading glasses to see up close beforehand, you’ll still need them afterwards (unless you opt for monovision, but you may still need the readers anyway).

LASIK just recently began to be practiced in the U.S. in 1996. It has been done for years in Canada and in Colombia, where it is now routine. The U.S. equipment is (in my opinion) inferior to that offered elsewhere, but is catching up in some cases (the Autonomous Technologies laser, with automatic eye-tracking, is at least comparable to the Chiron 217, but the capabilities of the two lasers may not completely overlap). In the fall of 1997, I had considered going to Colombia for an enhancement to my right eye and for initial treatment of my left eye, but due to difficulty in obtaining statistics (for both successful and adverse outcomes) for the surgeon of interest through his international coordinator, I chose to go to Dr. Jeffery Machat in Canada instead. Dr. Machat is brutally forthcoming about the kinds of things that can go wrong, and is up-front with his firm’s complication statistics. Between that and the fact that Machat is the most experienced LASIK surgeon in North America, and has spent a lot of time advancing the state of the art, I was sold. I should disclose that the fact that the enhancement was free under TLC’s lifetime guarantee was part of the decision.

LASIK was invented in Colombia by Drs. Virgilio Galvis and Luis Ruiz, who followed the earlier work in keratomileusis of Dr. Jose Barraquer, who is considered to be the “father of modern refractive surgery.” Galvis’s clinic claims to be able to treat myopia as bad as -25 diopters (D), hyperopia as bad as +17D, and astigmatism as bad as 9D (note that higher myopes may not get 20/20 vision, but they will be improved dramatically). (NOTE: A patient’s correction for extreme cases is highly dependent upon available corneal thickness. One must have a deeper ablation to correct higher errors, and it is not safe to leave less than about 250 microns of untouched tissue. Note also that the higher the correction, the smaller the fully-corrected zone may have to be, because wider ablations must be deeper, all else equal.) These claims are from Dr. Friedman’s page, and echo the laser manufacturer’s claims. I do not know if Dr. Galvis actually attempts corrections as extreme as those claimed. TLC’s claims are slightly more conservative, and they explain why at their web site.

By comparison, the most advanced machine approved by the FDA in the U.S., the VISX laser, is only approved for treating myopia of -1 to -12D and astigmatism of 1 to 4D. Many U.S. clinics that do not possess the VISX laser are using “astigmatic keratotomy” (AK) to correct astigmatism—this is similar to radial keratotomy in that a surgeon makes an incision into the cornea. I have to ask—if there are lasers available that will do the correction without using a scalpel, then why allow yourself to undergo AK?

Types of Lasers and Their Limitations

The VISX (even the new S2 machine) and Summit machines are broadbeam-type lasers, which use expanding cones of laser light to treat the cornea, and are limited to ablations of 6mm in diameter. Not all of this 6mm will be corrected to full power. Mild corrections may get a central zone of 3-4mm that is fully-corrected, with the rest blending upward to make a “ramp” to the (uncorrected) rest of the cornea, while stronger corrections may have a central zone of only 1-2mm, with the rest being blending. The reason for this, as explained above, is that more tissue must be removed for stronger corrections, so they will be deeper and will need a larger blending area to minimize edge transition effects that might occur were light to hit a sudden “step” where the corrected zone met the uncorrected zone. These lasers are currently used only for correction of myopia and astigmatism.

If the surgeon doesn’t take some pauses during treatment with a broadbeam laser to allow the plume created from ablation to dissipate, a “central island” may form, which means that not enough tissue was ablated in the very center of the cornea to provide full correction. Central islands often resolve themselves after a few months, but they sometimes require an enhancement to make them go away.

A potential artifact of the 6mm limitation is that patients who have large pupils in dim light may experience glare, arcs, starbursts, and halos at night, and may also suffer from night myopia because their eyes are gathering too much light from the uncorrected and blended parts of their corneas in comparison to the central corrected zone. Yes, that’s right—some PRK and LASIK patients need glasses to see clearly in dim light. Your surgeon should disclose this to you, if he’s honest.

The other kind of laser is the “scanning-slit” or “flying spot” style of laser. These lasers use a 2mm or smaller beam of light that is scanned around the cornea in a preprogrammed fashion to produce the correction. They are capable of ablations larger than the 6mm used by VISX and Summit, and many people claim that they produce smoother, more accurate ablations. Because they offer a larger treatment zone (for those patients with adequate corneal thickness), night vision artifacts are minimized (but the risk of having them is still nonzero). These lasers are in widespread use outside of the U.S., and most incorporate some kind of automatic eye-tracking to compensate for involuntary eye movements. Examples are the Chiron 217, Nidek, and Autonomous Technologies machines. Automatic eye-tracking has only been approved for one manufacturer (Autonomous Technologies) in the U.S. One group in Minnesota was doing investigational work with a Chiron 117 (the precursor to the 217, but itself a broadbeam laser) but was not permitted by the FDA to use the eye tracker on human patients. Scanning lasers can correct myopia, astigmatism, and hyperopia.

There is some development going on with solid-state lasers that work on a wavelength of 213nm instead of the 193nm that is used by Argon/Fluorine gas lasers such as Summit, VISX, and Chiron. Early tests by the FDA indicate that the 213nm lasers will do more “collateral damage” to surrounding corneal tissues than the 193nm lasers do. I would stay away from solid-state 213nm lasers if I were you.

Topolink and Custom Ablations

The latest research is in the area of linking corneal topographies directly to the laser to produce custom ablations for each patient. Currently, there are preprogrammed treatments for each refraction, and they treat a prototypical “average” corneal shape for that refraction. The topo-linked lasers offer the promise of treating each patient’s unique idiosyncrasies, and may be able to treat patients who have irregular astigmatism (either naturally-occurring, or induced from previous unsuccessful refractive surgery). As of this writing (August, 1998), topo-linked lasers appear to be about two years away from mainstream use.

LASIK and Mild Myopia

I sometimes get questions about LASIK for mild myopia. The biggest risk is a 1% chance of induced irregular astigmatism from an irregularly-healed flap (provided you choose an experienced surgeon). This complication can cause permanent loss of from one to four lines of best-corrected visual acuity, or BCVA (i.e., if you saw 20/15 with your glasses before surgery, then even though you may see 20/70 unaided after surgery, you might not see any better than 20/40 with glasses after surgery. That’s a significant blur, and anyone who tries to brush that risk under the rug is doing you a vast disservice. You might get relief from rigid gas-permeable lenses in this case, but if you’re one of the extraordinarily unlucky few with severe induced irregular astigmatism, you won’t. My experience at TLC-Windsor is that they are very blunt about this risk, and do not attempt to hard-sell you. The decision is yours to make. By the by, the risk increases to about 2.1% for myopes worse than -6.00D). If you already see very well with glasses or contacts, and see at least well enough to function reasonably well without them, then I would NOT get LASIK if I were you. Obviously, this cutoff point is subjective, and each person has to decide for himself if the expected improvement is worth the risk. I’d set a hard limit at 20/40 (the legal driving limit, representing, on average, -0.50D to -0.75D of spherical refractive error), and a softer limit at about -2.00D. Myopia this mild is very easily corrected with lightweight glasses or contact lenses. Of course, the presence of a lot of astigmatism changes things, but in the end, only you can decide if the risk is worth it.

LASIK vs. PRK

Some surgeons prefer to treat patients with myopia less than a certain amount with PRK rather than with LASIK, in order to eliminate the risks from flap complications. This is a personal decision between the you and your surgeon, but you should be aware that PRK carries markedly greater risks of permanent haze and scarring and a much larger infection risk than does LASIK. The risk of permanent haze and scarring increases markedly with the attempted correction, and is most often seen when PRK is attempted on patients whose initial refractive error was greater than -4.00D. The infection risk is not dependent on the amount of correction required. Furthermore, PRK patients are more likely to experience post-op pain, and take considerably longer to heal enough to have useful vision. This is balanced against LASIK’s 1% to 2% risk of flap irregularities that cause loss of BCVA, and which might not be correctable until the topo-linked lasers come on-line. (For mild irregularities, rigid gas-permeable lenses may help, but there are no guarantees. Note also, that a botched PRK may also result in irregular astigmatism that can significantly interfere with your daily life. There have been a few patients of both PRK and LASIK on the USENET newsgroup sci.med.vision who have had their lives significantly affected by bad outcomes—in one case, the patient is nearly suicidally depressed.)

Obsolete Methods

ALK, or automated lamellar keratoplasty, from which LASIK was developed, is now obsolete. I do not believe there is any legitimate use for it anymore. Similarly, RK, or radial keratotomy, in which radial cuts made by a diamond scalpel are used to flatten the cornea, is unconscionable now that laser techniques are available. The scarring from RK is horrible, the night vision is atrocious, and there is a very real risk of corneal rupture if the eye receives a blow (there is one noteworthy case of a police officer who had RK and whose cornea ruptured when his car’s airbag deployed!). A great many patients experience “hyperopic shift,” in which they get progressively more and mor farsighted. To a myope, that might sound like a good thing, until you realize that you’ll need thicker and thicker glasses to be able to use your computer, read labels at the supermarket, and read books and newspapers. RK is bad news. Run, don’t walk, away from anyone who wants to treat you with RK.

My Personal Experience

I first had LASIK performed by Dr. Stephen Siepser at TLC-Plymouth Meeting (Pennsylvania) in mid-June of 1997. The surgery was performed using a Chiron Automated Corneal Shaper (the microkeratome that cut the flap), set to cut the flap at 180 microns, and a VISX Star. This was before I had discovered sci.med.vision and learned the limitations of that machine. Dr. Siepser himself is an excellent surgeon, and the anesthesiologist with whom he most often does anterior segment surgery (cataracts, etc.) trusted Dr. Siepser enough to let Dr. Siepser do LASIK on him, which is a glowing endorsement if there ever was one. That said, Dr. Siepser is limited to what the VISX Star can do (broadbeam 6mm ablation to correct myopia and astigmatism).

Dr. Siepser operated on my right eye, and corrected it from -5.50, -0.25 to about +1.00,-0.25 initially (overcorrection is done to compensate for the regression that occurs during healing. Surgeons try to be conservative so that you end up right at 0.0 or slightly myopic.). Over a few days, this improved dramatically as the corneal edema went away, and I was seeing 20/20. I wore a soft contact lens in my left eye to provide balanced vision. After a month or so, I began regressing more and more myopic, and could only see 20/50. Clearly, I would need an enhancement. (NOTE: enhancements have the exact same flap risk of irregular healing and resultant loss of BCVA as does the initial LASIK procedure.)

After a lot of research, I decided to trust my eyes to Dr. Machat. Part of this decision was influenced by the fact that my pupils dilate to a maximum of 8mm when drops are used to dilate them, and they typically go around 7mm or more in dim light. Dr. Machat’s Chiron 217 can blend out to 9.6mm, so the risk of night vision problems would be reduced. I booked my surgery two months in advance for the U.S. Thanksgiving Day (which is not celebrated in Canada :-) in Windsor, Ontario. This was November 27, 1997.

Dr. Machat was able to lift the flap on my right eye from my previous surgery, and performed the enhancement (my eye had regressed to -1.50, -0.25 by that time). He then cut the flap on my left eye and did the initial correction to it. The surgery went without a hitch, and the Ativan I had been given kept my nerves well under control. After about 20 minutes in the waiting room, my flaps were examined under the slit lamp and I was sent to my hotel (my wife drove), where I slept for several hours. When I awoke, it was dark outside, but I could see very well to go to dinner, with no glare, arcs, starbursts, or halos. The acuity was startling and crystal clear—I could see as well as my wife, if not a little better (she has natural 20/20 vision, and can read 20/15 in strong light). When checked the next day, I was +2.00D, 0.0D in my left eye and +1.00D,0.0D in the right. Over time, this overcorrection has reduced, and I am now about +0.25D in each eye, with about -0.25D of residual astigmatism in my right eye. I have no night vision problems, except perhaps when I am extremely tired and my eyes are dry (then I see some small starbursts). In fact, on the way home from surgery, I made a game out of trying to read the mile markers on the Ohio Turnpike before my wife could (in some cases, I could!).

Summary:

* Beyond about 20/400, Snellen Acuity measurements are pretty meaningless. I gauged this based upon a homemade Snellen chart with some really huge letters.

** In good light, I can almost pick out 20/15 on my homemade chart when I’m well-rested and well-hydrated.

*** This result is questionable: prior exams have been done in a dimly-lit room, so that my pupils were somewhat dilated. This particular exam was done in a brightly-lit room, which causes the pupils to contract, minimizing any optical errors that may be present. This phenomenon is known to camera buffs as “depth of field”, and it is very much an issue for getting correct refractions at eye examinations. Your exam should be performed in a dimly-lit room so that depth-of-field does not mask any refractive errors you may have. I may switch O.D.s for this very reason—I was not impressed with my current doc (I switched docs due to moving across the state. My old doc was very good, but I can’t be driving 300 miles for an eye exam!).

If my cylindrical or spherical error in my left eye increases to 1 diopter or more, then I will probably have an enhancement, and I’ll go back to Dr. Machat to get it.

Of course, I am very happy with my results, BUT THERE ARE NO GUARANTEES THAT YOUR RESULTS WILL BE THIS GOOD. The odds are in your favor, but the risks are nonzero, and not everyone who has a successful surgery ends up with unaided 20/20 vision. 95% of all LASIK patients get 20/40 or better (some require an enhancement to get there), for reference. The chances for 20/20 improve as initial refractive error decreases. For typical outcome statistics (when experienced surgeons are involved), have a look at TLC’s website.

What You Experience During LASIK

Prior to the procedure itself, your local O.D. will have screened you for eye diseases, keratoconus, or retinal problems, all of which disqualify you for surgery. He will also have performed a cycoplegic refraction, in which he gave you drops to paralyze your eyes’ ability to accommodate, so that he can get a very accurate refraction. You should have ceased wearing soft contacts for at least one week prior to this exam, and hard contacts for at least four weeks, and you may not wear them again between the exam and your surgery (they can leave some residual misshapenness in your cornea that can cause inaccurate surgery). When you arrive at your laser center, a map, called a corneal topography, will be made of your eye. This map will be used to help the laser select a program, called a nomogram, to tell it how many pulses to deliver to various spots on your cornea to produce the intended correction.

Your refractive error will be double-checked, possibly by using an autorefractor, but definitely by hand with the phoropter (that funky mask-shaped device your eye doctor uses to determine your prescription).

You will be given drops to anesthetize your cornea, and measurements will be made by tapping your cornea with a pachymeter to determine your corneal thickness. You’ll see it, but you will not feel it. FYI, average corneal thickness is about 500 microns at the center, tapering to about 300 microns at the edges.

If any of the above checks are omitted, get up and leave! They are vital safeguards to make sure that you have a safe surgery with the best possible chance of a good outcome.

You will be given more numbing eye drops, and your face will be washed with an antibiotic cleanser. You’ll also receive antibiotic eye drops and either diazepam (the generic name for Valium) or iorezepam (the generic name for Ativan) to help you calm your nerves. I strongly suggest that you accept the medication, but make sure that you don’t take too much, because you need to be awake during the procedure! (Note contraindications for these medicines, however—your surgeon should be aware of them).

You will lie in the operating chair, which is motorized and will draw you up under the operating microscope and laser. The eye that is not being treated at the moment will be taped shut, and your operative eye will have its lashes taped back with a surgical drape. You will be given much more powerful anesthetic drops (usually Tetrocaine, a cocaine derivative). These sting a little until they take effect. The surgeon will ask you if you can still feel the stinging, and will continue to apply the drops until you can’t. Don’t be a hero! Your cornea is very sensitive, so make sure you get all the medication you need so that you feel nothing when your cornea is touched. Then the surgeon will insert a speculum to hold your eyelids open (Machat’s speculum is much more comfortable than the one Dr. Siepser uses, FYI). Relax and do not fight with the speculum. Do not squeeze it with your eyelids, just relax. Your relaxation (and the fact that you do NOT squeeze with your eyelids—ask your surgeon to give you guidance and feedback on this during the procedure, because you won’t realize you’re doing it) is crucial to getting a good cut when the flap is made (this is why you should accept the tranquilizers unless there’s a medical reason not to).

A couple of reference marks will be made on your cornea with a soluble ink. These are made so that the surgeon can properly realign the flap when he’s done. This happens very quickly—if you aren’t watching for it, you’ll miss it.

The suction ring will now be placed on your eye. It surrounds your cornea, and applies pressure to your eye so that the cornea is easier for the microkeratome to cut. About 60mmHg of pressure is applied (this is 3 to 6 times normal eye pressure, so if you have glaucoma or retinal problems, you should definitely bring them to your doctor’s attention beforehand, as this part of the surgery may be dangerous for you), and your vision blacks out. Do not worry! Your vision will return as soon as the suction is released, which will be only 10-30 seconds after it is applied! Make sure your doctor tells you when he’s about to start the microkeratome. Concentrate on breathing normally, to the exclusion of all else. This will help you control your nerves, if you happen to still be nervous. You must hold as still as you possibly can, and must avoid flinching, which will produce a bad cut. If you get a bad cut, the surgeon should smooth the flap back down, let you heal for three months, and then try again. He should not attempt to perform the laser part with a bad cut, because you will get a bad result. Don’t worry about this, and don’t clench your body up. If you just concentrate on taking regular, deep breaths, you won’t even notice that the cut has been made (when Dr. Machat did my left eye, the whole suction ring and cutting procedure went so fast that I had to ask him if he’d made the cut already, because I didn’t remember his having turned on the microkeratome!).

Thanks to your concentration on your breathing (normal, deep breaths) and the tranquilizers, you’ve controlled your nerves, and the surgeon has made a good cut. He removes the microkeratome and flips back the flap. Congratulations! You’ve just made it through the most difficult part of the procedure, and it was over in less than 30 seconds. You can see, but what you see is a blurry light (red for VISX, green for the Chiron 217) upon which you must try as best you can to stay focussed while the laser operates. The assistant will give you a running count of how many seconds of treatment are left, and many surgeons (including both Drs. Siepser and Machat) will take a pause every dozen seconds or so to wipe away any debris on your cornea and present a clean surface to the laser (this practice minimizes the risk of central islands and uneven treatment).

When the laser is done, the surgeon will rinse your cornea, then smooth the flap down with a tiny Weck cell sponge. He’ll spend some time and care with this, because it is critical to your final outcome. Then you will lie there for a few minutes while the cornea beds down, you’ll get more antibiotic drops, and the surgeon will remove the speculum when he is satisfied that your cornea is smoothly in place. Then the procedure is repeated on your other eye (unless you have chosen to have only one eye done at a time, which is rare but not unreasonable).

After the procedure, you’ll suddenly feel heavy and sleepy. Your adrenaline and anxiety from the surgery are over, and you’re relaxing while the tranquilizers take over. You will be put in the waiting room for about 20 minutes for your corneas to bed down some more, and may fall asleep. Your eyes will be checked under the slit lamp microscope to verify that your flaps are properly bedded down, and then you’ll be sent on your way, but you will NOT be allowed to drive, so make sure you have someone with you.

You will have a dark pair of wraparound sunglasses, which you should use every time you go outside for the first week. You should use good sunglasses regularly afterwards, since exposure to UV has been suspected in causing haze in PRK patients, and LASIK is similar enough to PRK that you don’t want to take a chance. In addition, you’ll be minimizing your chances of having cataracts or retinal problems later in life, all of which apparently are increased by exposure to the sun’s UV light. You will also have plastic eye shields that you should tape over your eyes every night before going to sleep so that you don’t rub your eyes and accidentally dislodge your flaps before the epithelium regrows over the edges (there’s a 50nm-wide “gutter” around the edge of the flap at first, that the epithelium must fill in and grow over. Eventually, this gutter will form a scar—don’t worry; it’s too small to see with the naked eye and too small to show up in your visual field. You will never see it, and only people who look carefully at your eyes under a slit-lamp microscope will be able to find it.). The first 5 days are critical—you do not want to dislodge the flap! After that critical period, you’re not going to move the flap without surgical tools (NOT that you should try!)—loose talk about rubbing your eyes and coming away with your flaps in your hands is hokum (barring complications that delay re-growth of the epithelium). You will also have some steroid drops, some antibiotic drops (ofloxacin is best), some artificial tears (patients in Canada get this nifty tear gel instead), and possibly a non-steroidal anti-inflammatory drop. Use them all religiously, and follow instructions. You can use the artificial tears as often as you like—use them liberally. Make sure you wash your hands before doing anything at all with your eyes, so that the chance of infection is minimized. An infection under the flap can cause scarring that can blind you, so do not screw around here!

You will probably want to take a nap. Go right ahead—you heal the fastest while you sleep. Use your eye shields! When you wake up, you will already be able to see quite well, and it should get even better over the next few days as your corneal edema (swelling) goes away. You may experience a mild burning sensation after a few days. This is the severed nerve endings from the cutting of your corneal flap re-growing. Avoid the urge to rub your eyes—try to soothe them by using refrigerated artificial tears instead (the coolness feels good).

The day after surgery, you will return to the laser center to have your flaps checked under the microscope and to have an initial refraction. If everything is OK, you’ll be discharged to the care of your local O.D., whom you should see when they tell you to (usually 3 days post-op, then 1 week, then 2 weeks, then 1 month, then 3 months, then 6 months, then 1 year). Don’t blow these visits off. If any complications arise, such as epithelial ingrowth, you’ll want to get them resolved right away.

Vision isn’t perfect the first day after LASIK. There is some post-surgical edema that causes a bit of haze, especially at night, when you see some halos around lights and have reduced visual acuity. This clears up within three months.

For about three months, you may experience fluctuations in your acuity. You may see really well one day, and not so well the next. Be patient— because there’s no blood supply, the cornea heals slowly. It can take three to six months for vision to stabilize. Don’t even think about getting an enhancement until at least three months have passed!

You may be a little farsighted at first, to compensate for regression during healing (on the flip-side, if you were hyperopic before, you may be a little myopic at first). Over the next few months, this will normalize itself and you should end up either emmetropic (i.e., neither near nor far sighted) or slightly myopic. You don’t want to end up very far-sighted, or else you’ll need reading glasses earlier than you otherwise would as you age. If you end up slightly myopic, it will be a blessing when you turn 45, because you’ll still be able to read most things without reading glasses.

A Note to Pilots and Military Candidates

At the current time, the Federal Aviation Administration permits (yes, permits) recipients of RK, PRK, LASIK, epikeratophakia, and IOL to hold commercial pilot’s licenses following a satisfactory report from the pilot’s ophthalmologist that the results have stabilized (this could take from one to six months after surgery) and meet FAA medical criteria. For further reference, please refer to the FAA’s Aeromedical Certification Update of March, 1998, titled “RK and Laser Visual Acuity Procedures,” by Dr. Warren Silberman, D.O., M.P.H. See also this note I received from an FAA employee.

A WORD OF WARNING: As documented in Jon Krakauer’s book, Into Thin Air, RK recipients will experience degradation of their vision at low atmospheric pressure. One climber, Dr. Beck Weathers, was effectively blind near the top of Mount Everest—his RK-treated corneas had so dramatically changed shape in the thin air that he could not focus on his feet (he was terribly farsighted at this point). He got lost in a sudden storm and spent a night in the open, exposed to wind chill of seventy degrees Fahrenheit below zero, and ended up losing one of his hands and all of the fingers of the other hand to frostbite. Hyperopic progression at altitude is a well-known problem with RK. If you get (or have had) RK, are flying at high altitude, and lose cabin pressure, you will be unable to read your instruments. If you’re a passenger who has had RK and the plane loses cabin pressure, you won’t be able to see the oxygen mask right in front of your face. This is yet another reason to avoid RK at all costs. Now that PRK and LASIK are available, there is no reason for anyone to ever elect to get RK.

(NOTE: I do not know if LASIK or PRK recipients will have the same problems as RK recipients at low atmospheric pressures. I don’t know that the question has ever been studied, and I would appreciate it if someone who does know would drop me a line.)

I have also recently been informed that refractive surgery is now allowed by the United States Armed Forces. However, it is NOT allowed for military pilots, and might not be allowed for divers and SpecOps personnel. If you fall into one of those categories, or if you want to, investigate this issue thoroughly.

Don’t think of having surgery and lying about it, either. In the case of RK, ICR (intrastromal corneal ring), and some ICLs (implantable contact lenses), the evidence will be visible to the naked eye during close inspection (as in, during your annual medical evaluation). In the case of PRK and LASIK, the evidence shows up quite clearly when a corneal topograph is made of the eye (the front of the cornea shows up as flatter for myopia patients, while the edges show up steeper for hyperopia patients). ICLs implanted behind the iris may be difficult to detect, but should show up rather dramatically when the iris is dilated for a routine retinal health examination. I’ll omit for now the discussion of increased cataract risks from this type of ICL.

Links to Detailed Technical Information

That’s the Cliff’s Notes version. For more technical reading, follow the links below. (NOTE: I moved Dr. Friedman’s site to the bottom of the list of links. In my opinion, his continual extolling of the virtues of Dr. Galvis on sci.med.vision, without disclosing that Galvis pays him to set up groups to go get the surgery, is unethical. Furthermore, getting information from Friedman about Galvis’s statisics (and particularly complication rates) and treatment techniques is like pulling teeth. His website downplays the risks, almost to the point of completely failing to mention them. Finally, the informational video I received from Friedman makes little to no mention of the things that can go wrong, and is big on testimonials. (Compare this to Dr. Machat’s video, in which Machat personally delivers TLC’s complication statistics). The rest of the links are to articles from Ocular Surgery News, The Journal of Refractive Surgery, and archives from the American Medical Association’s publications website.

The first link is the SurgicalEyes^TM website, which was established by people who have had poor results from refractive surgery. They have provided images of what their vision is like, and have also provided a list of personal experiences of others who have had poor (or even disastrous) results. You are doing yourself a grave disservice if you don’t read through their entire website before undergoing refractive surgery.

The second link is the “I know why all refractive surgeons wear glasses” web site, which contains a wealth of detailed information about what can go wrong in refractive surgery, as well as “quirks” that will be present in your vision even if you have an excellent result. I have a few issues with some of the content, and there’s little LASIK-specific information there (most of the information is relevant to PRK and much less so to LASIK), but on the whole, it is a very well-done and balanced web site. I cannot encourage you strongly enough to read through that site completely and carefully before you undergo LASIK or any other procedure. There are risks to refractive surgery, and, as I mentioned, there are some negatives even in a successful result (e.g., you may read 20/20 on the eye chart, but your night vision may be fraught with glare and halos, especially in the first few months post-op). The negatives may be lesser in frequency and severity with the more advanced treatments and hardware available outside the U.S. (the “I know why” web site doesn’t discuss foreign LASIK results—this is one of my issues with it), but I can’t say for certain, because everyone heals differently.

If you read nothing else, read those first two websites in their entirety.

A few things are worth repetition and emphasis:

• Despite all the advertising hype, not everyone gets a 20/20 result. In fact, truth-in-advertising would require that laser vision advertisements advertise “reduced dependence upon glasses or contacts,” and would require that no mention of something like “throw away your glasses” be permitted at all (the FTC has cracked down on some of the more egregious advertising, but there’s still a lot of hype out there). Somewhat less than 60% of PRK patients in the VISX FDA study achieved 20/20 or better after one treatment. (The “I know why” web site will tell you why I believe the VISX numbers are more trustworthy than the Summit numbers.) The FDA numbers for LASIK aren’t in yet, but they are expected to be at least as good, if not slightly better (the final correction in LASIK is much more predictable than it is with PRK, so the initial correction can be made much more precisely). There is no guarantee that you’ll end up 20/20. There’s a very large chance (95%) that you’ll be 20/40 or better, but if you aren’t willing to tolerate the chance that you’ll be one of the 35% or so that end up between 20/20 and 20/40, don’t get the surgery.
• 
  
• Even if you get 20/20 visual acuity, your vision still may not be perfect. LASIK is well-known for producing problems with night vision, including glare, halos, and a slight generalized blurriness when the lights go dim. Most of these problems go away almost completely within six months, but some people have permanent increases in night vision problems over preoperative levels, and almost everyone will notice some change for the worse, however minor. Night vision problems are subjective as well—what bugs the heck out of some people might not bother you at all, and vice-versa. These problems are reduced with larger ablation zones (6mm is really the minimum you should allow anyone to do), but there is a tradeoff: the larger the ablation zone, the deeper the ablation has to be to achieve the same correction. This leaves your cornea thinner than it might have been with a smaller ablation zone. Many surgeons believe 6mm is an ideal compromise, but patients needing lesser correction may be able to have their correction blended better with a larger ablation zone, alleviating a lot of these night vision problems. Note that no machine that is currently FDA-approved in the U.S. can make an ablation larger than 6mm. For larger ablations, you will have to get your surgery outside of the U.S. or at one of the few centers that is using an investigational laser such as the Nidek, Chiron 217, or Autonomous Technologies.
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• Refractive surgery can introduce astigmatism where you did not have it before, and it can be “irregular” to boot. Most astigmatism is “regular,” meaning that is is symmetrical with respect to the meridians of your cornea (if you don’t understand, the “I know why” web page can explain it). Irregular astigmatism is asymmetrical and is harder to fix—none of the current-generation lasers in the U.S. can fix it, and until topo-link is perfected, none of the 3rd-generation lasers elsewhere in the world can, either. Furthermore, glasses and contacts can only approximate a correction to irregular astigmatism (RGP contact lenses can completely correct mild cases, but even they have their limitations.). With respect to LASIK, this problem is caused by a flap that was not properly smoothed out when it was laid back down on your eye, or by irregular flap healing. A skillful surgeon is less likely to introduce this problem, but there are no guarantees.

Only you can decide if the risks and the potential lasting night vision problems are worth the chance to see much more clearly than you can now without glasses or contact lenses. In my case, I was so nearsighted at -5.5D that if I forgot where I put my glasses, I could not see well enough to find them. If you’re only a little bit nearsighted, my advice would be to forego surgery unless you really cannot tolerate glasses or contact lenses for some reason. For me, the risks were worth it—I can see when I wake up in the morning, and there is no fear of something happening to my glasses, and there is no hassle with a dried-up, sticky contact lens at the end of the day.

For what it is worth, my refractive surgeon does not wear glasses. :-)

Here are the links:

• Surgical Eyes. This site was founded and is maintained by people who have had adverse outcomes from refractive surgery (RK, ALK, PRK, and LASIK are all represented). Images of what it’s like to have some of the visual problems that can occur with refractive surgery are presented, as well as personal experiences. They have also set up some discussion groups for mutual support for people with adverse outcomes. This site, together with eyeknowwhy, provide the best possible informed consent you can have.
• “I Know Why Refractive Surgeons Wear Glasses”. (NOTE: This page has gone AWOL sometime in the recent past. If anyone knows where it went, please let me know.) This page carefully details the potential risks of refractive surgery, including the negative aspects that go along with successful outcomes. If you read nothing else, read everything at this site carefully. This site provides the best informed consent I have yet seen. The authors of this page have a friend who had a disastrous PRK outcome, and whose surgeon did NOT properly disclose the risks.
• TLC, The Laser Center. I don’t have many commercial links here, but this one is chock full of information, including realistic successful outcome expectations, hyperopic corrections, and TLC’s complication statistics. I used TLC, and I am very happy with the results.
• History and developments in the correction of vision
• OSN: LASIK is rising star in refractive arena
• OSN: LASIK called better than PRK for high myopes
• OSN International Edition: Patients are choosing LASIK over PRK
• PCON: LASIK, PRK go eye-to-eye in Saudi clinical trial
• OSN: Who should decide to perform LASIK or not
• JRS: Regulatory Considerations Regarding the Use of the Excimer Laser for LASIK
• PCON: Approach LASIK with caution, education
• OSN: LASIK, the future of refractive surgery
• OSN: Bilateral simultaneous LASIK is safe and effective
• OSN International Edition: LASIK shield protects hinge during astigmatic treatment
• OSN International Edition: Avoiding LASIK complications takes patience
• OSN: Patient's third enhancement procedure
• OSN: American team uses multizone LASIK to treat high myopia
• OSN International Edition: Restoring stretch to Bowman’s membrane reduces late-onset islands following LASIK
• OSN: Post-LASIK antibiotics must achieve deep penetration
• OSN: Superior hinge LASIK with new microkeratome improves safety
• OSN: Just how secure is the flap with LASIK?
• JRS: Histopathological Comparison of Photorefractive Keratectomy and Laser In Situ Keratomileusis in Rabbits
• Medical News & Perspectives - November 15, 1995 (c) AMA 1995
• Chiron Vision, makers of the Technolas Keracor 117 and 217 excimer lasers and the Chiron Automated Microkeratome
• Sci.med.vision newsgroup FAQ
• EyeWorld, a trade publication
• Hands on: Thirteen steps to a perfect LASIK for the beginning surgeon—Feature Article
• Refractive Tool Time: LASIK surgeons develop eye-opening speculum designs—Feature Article
• Brian’s Eye Tests—tests for abnormal/diseased eye function
• Physical and spatial aspects of night vision
• Friedman’s LASIK Page

This page © 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, and 2005 by Chris BeHanna. Copyrights of pages linked in above are owned by their respective copyright holders, including, but not limited to, SlackInc, the American Medical Association, Eyeworld, the author of the sci.med.vision FAQ, TLC, Kenneth Alexandor of Carnegie Mellon’s Computer Science Imaging Lab, SurgicalEyes, and Chiron Vision.

I have received no money for putting together this page. It is strictly for your information and education. I am not a medical professional; if you need medical advice, consult an opthalmologist. No warranties of any kind are offered for the information on this page.

Last updated 7 November 2005 (added 2004 and 2005 eye exam results, and reformatted to use CSS and proper XHTML).