Mastering Advanced Surface Ablation Techniques Ashok Garg, Frank Jozef Goes, Cyres K Mehta, Christopher J Rapuano
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Section 1
1Evolution and Resurgence of Surface Ablations2

The Excimer Laser as a New Surface ApproachCHAPTER 1

Arturo Pérez-Arteaga
(Mexico)
 
INITIAL SURFACE APPROACH
The main circumstance that lead the excimer laser to go inside the refractive surgery field was the fact that more than burning or cutting the material, the excimer laser adds enough energy to disrupt the molecular bonds of the surface tissue, which effectively disintegrates into the air in a tightly controlled manner through ablation rather than burning. Thus excimer lasers have the useful property that they can remove exceptionally fine layers of surface material with almost no heating or change to the remainder of the material which is left intact.
Because of these physic properties and thanks to people like Rangaswamy Srinivasan, the excimer laser went inside the refractive corneal surgery field 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, it means the surface approach, was the door of entrance of excimer laser in the refractive arena. 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 safer to perform refractive corneal surgery than other modalities of corneal refractive surgery used before.
But also during the first years 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 the early days of PRK:
  • The management of epithelium in different ways.
  • The need to control the postoperative pain
  • The need to avoid very deep ablations; at this time to avoid haze, and not as a biomechanical concept
  • The need to have large follow-up of our patients.
With success but also with complications we learned that the corneal surface had limitations and that this “reshaping of the future” was not as magical as we thought.
Then LASIK came from Dr Pallikaris to the excimer laser refractive surgery theatre. It was the technique that dominated refractive surgery for many years. The ophthalmic community started noticed that the flap-retaled complications were the most powerful 4complications of LASIK. Finally the long term complications started to occur, like the corneal ectasia or iatrogenic queratoconus. The LASIK experienced important reconsiderations worldwide. The inclusion criteria for stromal ablation decreased and so a new born of the surface ablative procedures came to the light.
 
ADVANCED SURFACE ABLATIONS
The history of humanity teach us that we learn much more from our own mistakes rather than our success. Recently at the American Academy Meeting 2006 in Las Vegas, Nevada, Marguerite B. McDonald, who pioneered PRK 20 years ago, outlined the reasons why she has recently returned to corneal surface ablation in a presentation titled “Why I hung up my microkeratome”. In this point of the history of refractive surgery, more and more surgeons worldwide are changing ageing their practice style to the surface ablations under the premise: if you do not have a flap, you can not have flap complications. Another important tool for this race back to the surface are the advantages of the flying spot pattern of laser ablation that decreased the problems experienced with surface ablation in the early days.
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 ageing 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 ageing to the refractive field Prof Palikaris from Grece with the epi-LASIK. Even he described the use of LASIK years before, recently he described a microkeratome able to perform an epithelial flap and so avoid the use of alcohol to do the detachment and of course avoid the cut of the corneal stroma. Because the epithelial cells were not injured with any chemical agent, 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 ageing to the surface of the cornea, avoid the use of alcohol (that is also aggressive 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 it self 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, the 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 permitting a re-epithelization process and controlling 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 desepithelization without the risk and expenses of the use of a epithelial microkeratome is now in the air.
Anyhow you are able to perform surface ablation, be sure to do it with a mechanical method instead a chemical one. With the new era of the surface ablation (Avanced Surface Ablation) many problems that were presented before like, corneal haze, pain and delayed visual recovery have been reduced. The surface ablation permits to work in thinner corneas rather than LASIK. In terms of efficacy the results of customized ablation treatments are also better with surface ablations that with LASIK.
Recently, the idea that a Sub-Bowman's Keratomileusis (SBK) will become the next trend in laser refractive surgery, combining advantages of 5both 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.
Still at this time visual recovery is slower with surface ablations in comparison to LASIK but the good communication with the patients is mandatory. We have to speak a long time with our patients regarding the long term benefits with the fact of taking care of the corneal biomechanics avoiding “to cut” the cornea. We must let them know by the other hand about the symptoms that they are going to experience during the first days and how to manage them; tell them that this is a worth attitude, because at the end we will have a long term healthy cornea. We must speak also about the depth of ablation according to their own pachimetry; they must know since the preoperative period how much corneal tissue will be ablate; they have to know that the success is not only a refractive result, it is also to obtain a planned ablation and a planned postoperative topography map.
 
Indications for Surface Ablations
There has been a change in indications for surface ablations with the new approach from recent years. The Advanced Surface Ablation (ASA) has incorporated new techniques, new methods for epithelial removal, new pre and postoperative care all of them in order to obtain best predictable results, less symptoms for the patient and less postoperative complications.
With this new approach we can currently be sure that all patients eligible for excimer laser surgery are suitable to be operated with some surface approach technique. Maybe we are now at one particular step of excimer laser surgery where the choose of the technique, between surface and stromal ablations, depended just upon the surgeon preferences.
Nevertheless still controversy is going on because of the possible side effects of surface ablation and for many surgeons worldwide, still LASIK is the first way to approach to the excimer laser surgery.
 
Methods for Epithelial Removal
First of all, the surgeon must dominate one or some of the methods for epithelial removal. Currently there are different methods:
  1. Amoils Brush
  2. Mechanical Scrape
  3. Trans-epithelial scrape-limited diameter
  4. Dilute alcohol
  5. Proparacaine
  6. Balances saline solutions (BSS)
  7. Epi-LASIK
Some method offers advantages over others, but finally we think that the surgeon must do the one that he is accustomed to use and manage, since the preparation in the preoperative period until the complete postoperative time.
 
PEARLS FOR THE CARE IN SURFACE ABLATION PATIENTS
The issues that the surgeon must take in count during the performance of surface ablation are:
  1. Pain control. For the pain prevention the surgeon has as part of the treatment some important medications.
    1. Use of non-steroidal anti-inflammatory drugs (e.g. Acular, Voltaren …).
    2. Oral steroids and analgesics.
    3. Cox II inhibitors (e.g. Celebrex …).
    4. Contact lens preferences.
    5. Comfort drops (diluted tetracaine).
    6. Narcotic-like medications in some particular patients.
  2. Speed of epithelial healing. The surgeon must take in count that each patient has a different speed of epithelial healing. The patient must know this fact since the preoperative period and the surgeon must take care of it during the first days of postoperative period.
  3. Haze prevention. Maybe haze is the worst complication of surface ablation and maybe the main reason why intrastromal approach has not end. Some methods to prevent haze formation are:6
    1. The choice of preserve or remove flap, in particular in epi-LASIK where the epithelial cells has not suffered the aggression of alcohol.
    2. Pre and postop vitamin C; it is well known the benefit effect of vitamic C over the corneal epithelium healing.
    3. Ice cold BSS. Used by some surgeons to decrease inflammatory process and so the possibility of haze formation.
    4. Topical steroids. It is well known that the benefit effect of topical steroids in the reduction of haze. For many surgeons the therapy must be followed for several weeks in order to decrease the inflammatory response.
    5. Mitomicin C (MMC). There is still controversy regarding the use of this medication. Many surgeons are using MMC but some others believe that if there is a respect for the depth of ablation and the postoperative medication, there is no need for the use of MMC.
    6. Oral steroids. The value of oral steroids maybe much more in the decrease of postoperative symptoms.
    7. Choice of best contact lens. The must amount of water in the contact lens, more oxygenation to the cornea and so more rapid epithelial healing.
  4. Topical steroids side effects. If we are talking about the possibility of the long term use of topical steroids, we must concern about the side effects of this medication. Some physicians like to use drops of antiglaucoma medication to avoid increase in the intraocular pressure but also as a help in faster visual recovery because of its pupilary effects, like brimonidine. Some others do not use medication if there is not an increase in the intraocular pressure. Anyhow the postoperative visits must be frequented to be in care of this situation.
  5. Enhancement time. There is always a controversy regarding the exact time to perform an enhancement. Sometimes the patient with undercorrection pushes too much to the surgeon because the impaired vision, but the surgeon must keep the mind cool and speak with the patient a lot, about the need to wait enough time to have a stable refraction and so improve, in case of an enhancement, the final visual result.
  6. Mithomicin use. If the surgeon finally decides the use of MMC, so much attention must be placed in order to achieve the exact concentration and the exact exposure time. Severe damage can be caused to the tissues if MMC is not used properly.
  7. PRK vs LASEK vs epi-LASIK. The decisión between the surface techniques should be troublesome. There are factors influencing this decision like surgical skills, time of follow up and economics between others. Anyhow we must maintain in our minds, like in other kind of surgeries, that the best technique for the patient is the better the surgeon can dominate.
  8. Haze treatment. Because haze is an important complication of surface ablations, the surgeon must prepare not only to take the measures in order to avoid it, like was purposed before; the surgeon also must know and manage the treatment strategies. If well the rule is that the possibility to produce haze is in direct proportion to the depth of ablation, sometimes it has been seen in low profundity ablations.
 
CONCLUSION
ASA appears to have more safety and stability that the first generation of surface ablations performed with excimer laser. New surgical techniques, new generations of machines, improvements in preparation and postoperative care, as well as new medications introduced for the attention of the patients, are achieving tools to increase the success.
As was shown by Richard J. Duffey, who presented the results of the 2006 survey of trends in refractive surgery during 2007 ASCRS meeting, there is an increase in surface ablation techniques; he showed that during 2006, 10% of respondents ASCRS members indicated that they did not perform wavefront-guided ablations, in comparison to 26% of respondents to the 2005 survey, where was indicated that they did not perform wavefront-guided ablations. In addition, LASEK/epi-LASIK saw a dramatic increase in volume, with about 207,000 procedures performed in 2006 compared with about 33,000 procedures in 2005.7
Maybe the 3 most important reasons that are leading the way to this change in excimer laser practice style are:
  1. Improvement in care of the patients who undergo through surface ablations.
  2. The increase in wavefront guided ablations, with better results in surface rather than stromal surgery
  3. The flap-related complications of LASIK.
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