Risks and Complications of Laser Refractive Surgery

Many of the messages I receive are about normal healing sensations. Here is the framework I use throughout this page.

Expected effects are part of the process. They are built into the biology of corneal healing, they follow a recognizable timeline and they subside. You get through them.

Complications are events that should not have happened. They require a diagnosis, treatment, sometimes a return to the operating room. They are rare, and most of my pre-operative work consists of preventing them from happening.

In between lies a gray area: an expected effect that lasts a very long time ends up becoming a problem. Three weeks of dryness is part of normal recovery; disabling dryness at one year is something else. The difference lies in duration and impact, not in the nature of the symptom.

Infection

This is the complication patients fear most, and it is extremely rare. Thank God, I have never had one in any of my patients. I would add something from my own background: I worked for five years at Cochin Hospital, three of them as head of the cornea department, and I never saw an infection there that followed refractive surgery. The infectious keratitis cases I treated came from contact lens wear, trauma, or vulnerable patients.

Surgery is performed under sterile conditions, and a topical antibiotic treatment is used as eye drops for two weeks after surgery. A corneal laser does not enter the eye: it stays at the surface, without opening the inside of the eye.

A corneal infection, when it occurs, can be treated: antibiotic eye drops, sometimes fortified preparations, sometimes a surgical washout of the interface after LASIK. Itshows up as pain that increases instead of decreasing, a red eye and a drop in vision, generally in the first week. You call me the same day.

Dryness that sets in

Cases of dryness persisting for several months are rare. I have had a few, and it has always eventually settled down, sometimes after six months, sometimes after a year.

When dryness sets in, I do not just prescribe artificial tears. There are enhanced tears, tear gels for the night, an anti-inflammatory eye drop, punctal plugs that keep tears in the eye, and an oral treatment that is useful in certain patients. Inserting the plugs takes a few seconds and does not hurt.

One mechanism is worth knowing about. Marked dryness is often accompanied by an inflammatory reaction that damages the surface of the cornea. This irregular surface diffracts light and creates astigmatism that can be measured at the check-up. It then feels as if the surgery has failed: it is the surface that needs treating, and vision returns once it is treated.

Undercorrection and overcorrection

The cornea heals, and healing retains an element of unpredictability. Sometimes part of the correction is missing, or the result slightly overshoots the target, generally by about half a diopter. This is more common with high corrections.

In my practice, it is rare. I operate on about 400 patients a year and I perform fewer than one enhancement a year in nearsighted and farsighted patients. It is a little more common after presbyopia correction, and it remains low.

The approach is always the same. We wait for stabilization, we measure objectively, and we decide. It is too early to talk about an enhancement before the end of the first six months, because part of the deviation corrects itself spontaneously. A simple pair of resting glasses is sometimes enough. Otherwise, we go as far as a laser enhancement.

Regression

The correction applied by the laser is lasting: the tissue removed does not grow back and the new curvature is maintained. What can change is the epithelium, the superficial layer of the cornea, which thickens again over the years and compensates for a small part of the ablation made beneath it. For a modest correction, this is on the order of 0.25 to 0.50 diopter over ten to fifteen years. A -1 nearsighted patient will almost never regress beyond -0.10 or -0.20 diopter, which has no visible effect on vision.

The higher the initial correction, the more regression is possible, particularly beyond -6 diopters of myopia, +4 of hyperopia or -2 of astigmatism. A -8 nearsighted patient who drifts back to -0.75 remains very happy with the result, and a laser enhancement is still possible if corneal thickness allows.

Two different mechanisms can bring back a small correction, and they are often confused.

Epithelial regression. This is the one I just described. The epithelium, the superficial layer of the cornea, thickens slightly again and offsets part of the laser's effect. It is the operated cornea that changes, not the eye. This phenomenon was significant fifteen or twenty years ago, with older generations of lasers. With the Schwind platform and current treatment profiles, it has become rare in simple and moderate myopia, and it remains moderate in high corrections.

Progression of the refractive error. Here, it is the eye itself that keeps changing, independently of the surgery, as if you had not been operated on and were changing glasses in a few years. For myopia, this mechanism is linked to the lengthening of the eye, which almost no longer occurs after age 23 or 24. An example: if you are at -2.00 today and your theoretical need were to go to -2.50 in ten years, you would be at -0.50 ten years after surgery. You willnot go back to your initial myopia.

That is why I look at the history of your eyeglass prescriptions during the assessment. And if the combination of the two brought back some discomfort after several years, an enhancement would still be possible in most cases.

Myopia: stability and progressionHyperopia and its laser correction

Loss of lines of corrected visual acuity

Your corrected visual acuity is the best you can see with the best possible correction, in glasses or contact lenses. It is the maximum your eye is capable of. Myopia, astigmatism or hyperopia do not change this maximum; they only prevent you from reaching it without correction.

The goal of surgery is to let you see without glasses what you used to see with them. A residual correction, regression or remaining astigmatism can be made up for with glasses or an enhancement. Losing lines of corrected acuity means that this maximum itself goes down, and no optical correction can make up for it.

This can happen after irregular healing, a corneal opacity, or a poorly managed complication. It is rare, and it is what the pre-operative assessment seeks to rule out first and foremost. A drop of one line during healing, on the other hand, is common and temporary.

Corneal ectasia

This is the most feared complication of LASIK. It has its own section, further down.

What ectasia is

Keratoconus is a progressive deformation of the cornea, which thins and bulges into a cone. It degrades vision irregularly, in a way that is difficult to correct with glasses. Post-operative ectasia is the same phenomenon, triggered or accelerated by surgery on a cornea that was predisposed or weakened too much. It is what every refractive surgeon seeks to avoid, because the treatment is heavy: rigid contact lenses, cross-linking, intracorneal rings, and in advanced forms, a corneal transplant.

A normal cornea, operated on according to the rules, does not become ectatic. Ectasia occurs in predisposed corneas that the assessment did not detect, in corneas too thin for the correction removed, or in the presence of chronic, repeated eye rubbing. I work on these three points.

First safeguard: pre-operative screening

The pre-operative assessment is not only used to check your correction. Above all, it is used to examine your cornea closely enough to identify those that should not be operated on.

Topography measures the curvature of your cornea point by point, on both of its surfaces. Advanced forms of keratoconus are obvious. Early forms, which do not yet cause any symptoms, require a trained eye: a subtle asymmetry between the two halves of the cornea, a localized thinning, a back surface that stands out.

Epithelial thickness mapping is my favorite test on this subject, and it is rarely performed in general ophthalmology. The epithelium, the superficial layer of the cornea, has a remarkable property: it compensates for irregularities in curvature. Over an area that is beginning to bulge, it thins to smooth out the relief, which masks the emerging deformation on curvature tests. Mapping it point by point amounts to removing this camouflage. A localized epithelial thinning over a bulging area is one of the earliest signs I have. This test is systematically part of the assessment at the Institut Voltaire, and it is what allows a decision on borderline corneas.

Added to this are pachymetry, mean and maximum keratometry, analysis of the back surface, and the indices calculated by topographers. There are dozens of formulas estimating the risk of post-operative ectasia, each giving more or less weight to one parameter or another, and none of them decides for me. My role is to review all these values comprehensively and to make a diagnosis of suitability for surgery. If it were just a matter of looking at corneal thickness or a score on a sheet, it would be a little too easy.

My training in corneal surgery, at the Hôtel-Dieu under Prof. Bourges, at the Fondation Rothschild with Prof. Gabison and Prof. Gatinel, then as Chief Resident (Chef de Clinique) at Cochin, taught me to spot these signs and to distinguish true positives from false positives. Refusing to operate on a patient who is perfectly suitable for surgery is also a mistake. When a case raises a question, I do not decide alone: at the Institut Voltaire, I work with Dr Camille Rambaud and Dr Romain Nicolau, who are also refractive surgeons, and we discuss borderline cases together every week.

Second safeguard: the residual stromal bed

The residual stromal bed is the thickness of intact cornea that remains beneath the treated area, and it is what guarantees the mechanical strength of your eye over decades. The calculation is simple and I do it for each eye. We start from the total thickness of your cornea, on average 525 microns. In LASIK, we subtract the thickness of the flap, on average 110 microns, sometimes reduced to 100 microns, or even 90 or 80 microns in very rare complex cases. We then subtract the ablation, about 15 microns per diopter of myopia corrected, a value that also depends on the diameter of the optical zone. What remains is the residual bed.

Traditional guidelines set the safety limit above 280 microns, and more recent work conducted in London has shown that a 250-micron bed in a regular cornea remained safe. I prefer a stricter approach and I set my limit at 300 microns, so that this risk is as low as possible.

The laser software simulates the ablation and displays the expected residual bed before each treatment. I check this value eye by eye, and when it falls below my limit, I change technique. TransPRK does not sacrifice a layer of stroma in a flap and preserves, for thesame correction, about sixty microns more. When that is not enough either, I do not operate with the laser.

The “RST manager” of the Schwind laser, on an anonymized case. The software starts from the thickness of the cornea (552 microns), subtracts the thickness of the flap (110 microns) and the ablation depth (134 microns), and displays the stromal bed that will remain: 308 microns. It is this calculation, done for each eye, that rules out the risk of ectasia.

Third safeguard: eye rubbing

This is the most underestimated factor, and it is the one you have control over.

There is a predisposition to corneal deformation, which can be hereditary. But there is no progression to keratoconus in the absence of rubbing. This is the “no rub, no cone” theory, championed by Prof. Gatinel, one of my mentors. The gesture is not always conscious: rubbing on waking up, allergic itching, sleeping on your stomach with your head in the pillow, a hand or elbow under the eye during the night, rubbing in front of screens. What matters is strong pressure applied to the eyeball. Gently running your fingers around the eyes is not a problem, preferably on the bony rim of the eye socket, and this is the habit I teach my patients to adopt after the procedure.

When topography shows a sign of fragility, I look for a habit of this kind, and it then becomes a topic of consultation in its own right. Identifying and changing it is sometimes enough to stabilize a fragile cornea and to make surgery possible after a few months of follow-up. When the itching comes from an allergy, antihistamine treatment often solves the problem.

After surgery, I recommend that all my patients limit rubbing for good. It is general eye hygiene advice, and I also give it to people I do not operate on.

And cross-linking

Cross-linking strengthens the bonds of corneal collagen and is used to stabilize progressive keratoconus.

I reserve it for certain cases, especially in young patients, under 25. In a teenager who will not follow the instructions about rubbing, the indication seems solid to me. In an adult who has understood the mechanism and who really stops rubbing their eyes, I am more reserved, because keratoconus rarely progresses once rubbing stops. If progression is demonstrated nonetheless, the indication becomes legitimate.

What this means in practice

A thin but regular cornea, with a small correction to remove, keeps a comfortable residual bed and can be operated on with LASIK. A thick cornea that shows an unexplained asymmetry will be steered toward surface surgery, or not operated on. A regular cornea at 490 microns can be more suitable for LASIK than an irregular cornea at 520 microns.

The pre-operative assessment in detail

If laser is not possible: the alternatives

It happens: a flawless cornea, an excellent measured acuity, and someone who is not happy. This situation does not appear on any list of complications, and it deserves to be dealt with like the others.

Expectations that do not match what the technique can achieve

The mismatch happens before the surgery. A 45-year-old nearsighted patient who comes in to never wear glasses again will be disappointed if their distance vision is corrected without discussing their presbyopia. Someone who hopes for perfect vision in all circumstances, day and night, without the slightest halo, will find the first weeks long.

During the assessment, I compare what you expect with what surgery can achieve for your eyes, and I tell you when the gap is too wide.

The compromise for presbyopic patients

Correcting presbyopia with laser means giving something up. With monovision and blended vision, one eye sees well at distance, the other sees well up close, and the brain combines the two. With a multifocal profile, each eye spreads light over several distances. In both cases, we do not recreate the vision of a 25-year-old: we trade a little distance comfort for near-vision independence.

Most patients find the trade largely worthwhile, but in rare cases some do not adapt. I have nearsighted patients test the compromise with contact lenses before surgery, when the strategy lends itself to it. A pair of occasional glasses remains useful for demanding tasks, subtitles at the movies or prolonged reading. When the compromise still does not suit, we can intervene again after a stabilization period of at least 6 months. This enhancement ranges from a simple readjustment to a complete reversal of the treatment; that is the advantage of Schwind's PresbyMAX platform.

Patients for whom I think the result will be disappointing

I sometimes refuse to operate on someone whose eyes are perfectly suitable for surgery. A patient with very mild myopia who hopes for a radical change will be disappointed by an improvement their eyes cannot produce. Someone whose main complaint is eye strain due to an unsuitable correction does not need laser surgery; they need good glasses. Someone who comes reluctantly, pushed by those around them, has nothing to gain from having surgery now. In these cases, I say no, or I suggest waiting.

What I do when a patient is not happy

I see them again, as many times as necessary, free of charge, and I measure objectively. A complaint compared against a refraction, a topography and an examination of the surface almost always yields an explanation. In many of these situations, the cause is not the laser treatment itself: it is dryness affecting the surface, accommodative fatigue that resolves with resting glasses, residual astigmatism that is still regressing, a slower-than-average recovery. Each has a solution, and none requires going back to the operating room. When a repeat procedure is justified, we do it, but not before the end of the first six months.

You can reach me

Phone and WhatsApp:01 84 80 28 04. By email:nahaisi@laservisionparis.com. Or through Doctolib messaging.

I answer personally, including in the evening and on weekends. WhatsApp is often the easiest, and a photo of the eye sometimes saves you a trip across Paris.

I see you again

Post-operative follow-up is unlimited and included in the fee for the procedure. You come back as many times as necessary, including years later. The first check-up takes place on the Monday afternoon following the Friday surgery, sometimes on Wednesday or Thursday.

We can often sort things out remotely. When it persists, I prefer to see you within the following days.

I perform a repeat procedure if necessary

An enhancement is possible in most cases, after complete stabilization. After LASIK, by lifting the existing flap and readjusting with the excimer laser. After TransPRK, on the surface. After SMILE, with TransPRK or by secondarily creating a LASIK flap, depending on the case, never by creating a new lenticule.

The enhancement is included in the initial fee for the first year, then offered at a preferential rate up to 5 years. If urgent action is needed, a flap to reposition for example, we go back to the operating room without delay and without any discussion of fees.

I do not leave you alone with a problem

When a situation calls for a second opinion, I say so and I arrange it. I discuss it with my colleagues at the Institut Voltaire, I refer you to a specialist when necessary, and I continue to follow your case.

Fees, quotes and complementary health insurance reimbursement