The Return the Corneal Surface: The Evolution of Excimer Laser SurgeryCHAPTER 1

This field has been in constant evolution trough the years, since the first descriptions of altering the corneal curvature in order to obtain a reduction in a refractive error, to our days, when comprehensive input of data inside an excimer laser machine can guide to individualized refractive ablations and obtain the new goal in refractive corneal surgery, the 20/10 of uncorrected visual acuity with aberration-free vision. This was the dream of LASIK.

New understanding of corneal biomechanics is guiding currently to leading ophthalmic surgeons worldwide to “avoid the cut of the cornea” in order to avoid unpredictable biomechanical changes that can produce since alteration in the topographic pattern, until true corneal disasters. Also new studies are demonstrating the safety of surface ablations (e.g. no flap-related complications, new generations of excimer laser machines, broad range in medical indications like thinner corneas) and the increase in terms of efficacy, in particular with the results of customized ablation treatments. That is why the title of this chapter, “the return to the corneal surface”.

What we have learned through the years is forcing to us to do the things much better than we did in the past. At the end of the day, those who come to us are healthy people with almost healthy eyes that are able to see with glasses and we must be sure that we improve their vision without causing any damage; it is a matter of trust, respect to the history and ethics with humanity.

The main concept inherent in these points is that the cornea is a biomechanical entity and that we are obtaining a refractive result because we are changing the surface shape, and this change in the surface shape is because we are changing the corneal structure. The incisions alter 4the corneal structure and then a biomechanical response is the cause of the refractive change of the eye.

We learned, from our own mistakes with this incisional technique, to make of this biomechanical response of the cornea a predictable factor in order to improve the vision of our patients. After many disasters we learned to manage some key factors for the success, like selection criteria (e.g. range of diopters, preoperative K readings, corneal pachimetry), surgical technique (number, place, large and depth of the incisions) and postoperative care. At the end of the day, the nomograms made of this procedure a “cooking book” and we forgot that in each patient we were performing RK, a biomechanical response to an alteration in the corneal structure was the real responsible of the refractive changes.

Maybe if we were able to keep this in mind in the early days of Excimer Laser Surgery (ELS) and LASIK, we were be capable to think that the final refractive status was not only the result of our ablation profile performed over the center of the cornea as was purposed; it was-it is and it will be- the result of the biomechanical response of the cornea due to the changes we are doing in its structure. But we forgot this concept and we only learned to think as a nomogram; “if I place the incisions in this manner I will obtain this refractive result”; “if I ablate this amount of corneal tissue I will obtain this refractive result”. This “nomogram” way of think, was the cause of big disasters in corneal refractive surgery, not only in RK, but also in the ELS era.

I do believe this was the main lesson that RK leave us and now with all that we know about corneal biomechanics we are more capable to understand and appreciate. Now we do not have any excuse to generate disasters.

The idea of obtain a refractive result as a product of a corneal thinning was a very innovator concept; as in RK, the final result of KM was to increase the radius of curvature of the cornea making it more flat to decrease the inherent refractive power, but in a very different way that RK worked; the era of corneal removal of tissue was starting.

At that time there was impossible to think in corneal topography and even more, corneal elevation topography in order to preoperative evaluate the cornea of the patients. I can remember very well all the set of instruments for KM in situ, that Luis Ruiz bought to my country at the end of the 80s based only on external corneal curvatures. It was impossible to know and demonstrate at that time all the biomechanical phenomena induced in the cornea with the tissue removed; now we know that the biomechanics of the cornea is disturbed only with simply cutting the flap, without any tissue removal.

I remember few years ago talking with Carmen Barraquer during a meeting, that she was telling the audience that her father described the KM procedure only for healthy corneas; I think everybody now is agree with this concept, but we can be agree at the present time after all we have learned from our own mistakes in the preoperative evaluation of our patients and the new methods of study the anatomy of the cornea; now concepts like form of frustus keratoconus and margin pellucid degeneration, between others, are common now in the refractive surgery centers. But at the J.I. Barraquer times, how we were able to speak about a healthy cornea? What I mean is that we started to perform a procedure in our patients without the complete knowledge of its consequences. Arn't that a shame?

The most important concepts that KM brought into the refractive surgery field were:

As a final concept of this section I will only add that despite the medical knowledge and techniques described and performed in order to change the corneal architecture to obtain a refractive result, the newborn refractive surgeon learned in this non-laser period of the procedure 5to do something that he was not used to; to fee a patient for take out his glasses! This moved to the general public, the ophthalmic community and the big companies of ophthalmic supplies to the business field. Many people started to see this new growing field in the medicine as a matter of enrichment and not only as a benefit for some particular patient. Unfortunately until our days, many ophthalmic surgeons and laboratories are in this race, thinking first in the economic benefits rather than a real medical improvement of the population.

Because of these physics properties and thanks to people like Rangaswamy Srinivasan, the excimer laser went inside the refractive corneal surgery and it has been accepted worldwide. Nevertheless the ophthalmic surgeons must never forget that we are disintegrating live corneal tissue each time we are performing an excimer laser procedure.

Photorefractive keratectomy was the door of entrance of excimer laser in the refractive field. Methods for epithelium removal were then described in order to lead the excimer laser be in complete touch with the sub-epithelial tissue.

We started to notice the benefits of excimer laser surgery like predictable ablations, the easy way to perform this surgery, the well controlled reshape of the cornea and the stability of the refractive results; it became more predictable, easier and a safer way to perform refractive corneal surgery than RK.

By the other hand we started to fight with some new troubles with this technique like pain and delayed visual recovery because the epithelial management; also the phantom of haze appeared. We started to notice that it was not a free-complications procedure; our first way of thinking that it will be a technology able to correct “every possible refractive error” without complications, started to change.

At the end of this step we learned from PRK:

As a matter of fact we learned that the corneal surface had limitations and that this “reshaping of the future” was not as magical as we thought.

It was an era of great excitment; because the haze was avoided, the visual recovery was inmediate. Finally a free-of-pain procedure, a tremendous felling of a safe technique ran worldwide. Because there was almost not scar reaction inside the stroma, the amount of depth in the ablation was (at less it appears) not a trouble any more; maybe the dream of correction of any kind of refractive errors was again almost a true. To perform the cut the cornea, the statements mentioned by Barraquer years before were followed.

The refractive industry experienced a fast growing phenomena. Multiple models of excimer laser machines and microkeratomes appeared in the marquet; it was almost impossible to test each and every model; each company demonstrated that “their way to cut” was the best. The idea of avoid the blade to cut the cornea guided the studies to the phemtosecond laser, but with the same theoretical principle.

During this period appeared in the refractive field a tremendous advance; with the idea to perform better custom ablations the flying spot machines started to work; at the end this will be one of the routes to return to the corneal surface in a safe manner. So the custom ablations 6were a reality and so new ways to approach to the refractive ablations like the wavefront-guided and the topography-guided treatments started to demonstrated consistently superior results in comparison with the non-guided procedures, in controlled scientific studies.

Now we know that we started to perform LASIK with few information in the preoperative evaluation: the refraction, the corneal pachimetry and a topographic map of the surface of the cornea were enough at that time; at that time we were not able to think moreover. The step ahead in the custom ablations and the long-term flap-related complications that we started to see, permited to arrive new tools to the refractive preoperative evaluation; elevation topography started to be the standard of care in preoperative study. This was the way we opened our eyes to what we were really doing cutting the corneas and performing deep ablations.

I remember I told my working team at those years that we were starting to perform LASIK: at this time we are only seeing the good side of the procedure, but within the next few years we will start to see complications that currently we are not able to imagine.

The complications starting to emerge and new questions arise in the refractive field. The inmediate complications were about the corneal flap management in special situations, but the most severe and mediate complications were in the permanent alteration of the corneal biomechanics. We did not take in count these corneal biomechanics concepts when we started to perform LASIK worldwide; when we heard and read about the concepts in the alteration of corneal lamellae, millions of people were operated around the world. Arn't that a shame?

A lot of voices emerged trying to stop us; may be the strongest one was Cynthia Roberts, from Colombus, Ohio. The editorial “The Cornea is Not a Piece of Plastic” emerged like cold water to our way thinking about what we were doing with the cornea. She demonstrated some important facts:

May be the most important fact regarding LASIK is that the characteristic red ring pattern in the topographic map appears after the creation of the flap and without any laser ablation. Cutting the corneal flap alters the corneal structure permanently as a biomechanical phenomenon.

But the worst was still to come; the coolest water were those patients who underwent LASIK by us 3 or 4 years before. They arrived again to our office with iatrogenic corneal ectasia. This social and medical fact affected my practice and my way to animate. How can I explain to my family that my work is to improve my patients's vision and at the end they are worst that they were before my operation? How can I support this heavy weight upon my shouders? The medical behavior to these patients must be of total support until the end; even if corneal transplantation is needed the surgeon must be with them always; communication and a totally true information is mandatory. After some years my patients with keractasia are still alive, some of them with corneal transplant, some others with intracorneal rings, and some others with medical management and contact lenses. It is really a nightmare if you really cares….

Many surgeons learned the new rules and learned to respect them, even the range of candidates for refractive surgery decreased significantly with this new reality; unfortunately some did not change their mind. Until our days, sometimes the economics are over the well-being of our patients.

The “kind of magic” of the visual recovery of LASIK, was not a totally true statement. At the end of this period we learned that the fact of cut the cornea has several consequences if is not done in the proper way and in the appropiate cornea. Ourselves as surgeons, unfortunately have colaborated to the decrease the prestigious of the Laser Refractive Surgery. The most expensive trial in the history of ophthalmology ended last year in the United States and it was because a iatrogenic corneal ectasia after a LASIK surgery; can you imagine the amount of money to be paid by the surgeons (or the insurances companies) if every patient with loss of best corrected visual acuity because a flap-induced biomechanical damage to the cornea, will establish a trial?7

The first attempt to go back to the surface was from Massimo Camellin in Italy. He developed the LASEK technique; he described the use of alcohol for the epithelial detachment to obtain a complete epithelial flap which is replaced again over the cornea after the ablation. The idea of decrease the problems of the early days of PRK like delayed visual recovery, pain and haze with the fact of replace the epithelium was very attractive. Unfortunately, if well some controlled studies demonstrated that the pain was less with LASEK in comparison to PRK, the main problem was the death of the epithelial cells; so at the end we had to wait until the formation of a new epithelial layer under the dead one in the outer surface. At this point the studies demonstrated that the death of the epithelium was because the use of alcohol.

Then came again Dr. Palikaris from Greece with the epi-LASIK. He described a microkeratome able to perform an epithelial flap and so avoid the use of alcohol to do the detachment. Because the epithelial cells were not injured with any chemical he proposed that the epithelial flap was alive and so the replacement of it over the cornea can assure an easy attach. The main advantage of the epi-LASIK was to make an easy transition again to the surface of the cornea, avoid the use of alcohol (that is also agressive with the corneal stroma, and not only for the epithelium) and to produce a very smooth sub-epithelial surface to apply the ablation. But finally we saw that what really kills the epithelial cells is the detachment itself and not only the alcohol, so recently the discussion about replace or not to replace the epithelial flap emerged. Some surgeons are currently replacing the epithelial flap in favor to obtain less postoperative symptoms, even they are observing at the end of death of this first epithelial layer and a second one (new) emerge; by the other hand some other surgeons prefer to cut the flap at the end of the procedure permiting a re-epithelialization process and controling the postoperative symptoms with medication and bandage contact lens.

After all this discussion the idea to detach the epithelium with some mechanical method (non-chemical) that lead the same result of desepithelialization without the risk and expenses of the use of a epithelial microkeratome is now in the air. In our particular case we are detaching the epithelium with a blunt instrument with only anesthetic eyedrops and protecting the eye with bandage contact lens. We found easy, reproductible, safe and cheap and is our technique of choice at this time (please see video of this chapter).

Anyhow you perform surface ablation, be sure to do it with a mechanical method instead a chemical one. With the new era of the surface ablation many problems presented before like, corneal haze, pain and delayed visual recovery have been reduced. The surface ablation permits to work in thinner corneas rather that LASIK. In terms of efficacy the results of customized ablation treatments are also better with surface ablations that with LASIK.

Still at this time visual recovery is slower with surface ablations in comparison to LASIK but the good communication with the patients is mandatory. At least in my personal practice now I speak a long time with my patients regarding the long-term benefits with the fact of taking care of the corneal biomechanics avoiding “to cut” the cornea. I advertise by the other hand about the symptoms that they are going to experience during the first days and how to manage them; I tell them that this worth because at the end we will have a long-term healthy cornea. I speak also about the depth of ablation according their own pachimetry; they know since the preoperative period how much corneal tissue will be ablate; I speak with them that the success is not only a refractive result, it is also to obtain a planned ablation and a planned postoperative topography map.

We have foud in our practice a safe (if not a complication-free) ablative refractive technique and we think that each time more and more surgeons in the world are changing to advanced surface ablation.8

Recently, the idea that a Sub-Bowman's keratomileusis will become the next trend in laser refractive surgery, combining advantages of both PRK and LASIK, merged. Eyes treated with the SBK procedure showed decreased postoperative dry eye, lower reported corneal sensitivity, similar amounts of higher-order aberrations and a higher rate of overall patient satisfaction, according to investigators. Are we now moving beyond PRK and LASIK? Maybe this procedure will be the future…

The success of our laser refractive surgery is now depending of our real knowledge of what we are doing. We did in the past years some techniques without the complete knowledge of the corneal biomechanics and so the potential complications. It happened all around the world. Maybe we can have for ourselves and for our complicated patients the excuse of the ignorance; nevertheless these complicated patients were, are and will be, our entire responsibility as long as we live.

But now, after we have learned from the experience of others and ourselves one, if we do continue altering the corneal biomechanics, it will be an unforgiving act.

Here, at the end of the chapter, let me put some words of Cynthia Roberts: “the future of customized laser surgery is bright, but we must step into the future with a better understanding of our current procedures, rather that leap without knowing were we land”.