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Epithelial Flap Hydrodissection and Viscodissection in Advanced Laser Surface Ablation (ALSA)

Richard C.Rashid, MD

West Virginia University School of Medicine,

Charleston Division

Charleston, WV

INTRODUCTION

Laser in situ keratomileusis (LASIK), currently the most common refractive surgery world-wide, is performed by 50% of The American Society of Cataract and Refractive Surgery (ASCRS) members, and of those performing more than 5 procedures per month, approximately 2% performed laser subepithelial keratomileusis (LASEK), yet 45% of ASCRS members plan to perform LASEK in the future, according to Duffey (1), who analyzed the 2002 ASCRS survey for refractive surgery trends.

The evolution of LASEK began in 1949 when Dr. Jose Barraquer began his refractive keratoplasty techniques, followed in 1961 by the keratomileusis freeze-lathing procedures, then Dr. Luis Ruiz automated Barraquer’s microkeratome and automated lamellar keratoplasty (ALK) gained mild acceptance in the late 1980s to mid 1990s. The next evolutionary stages began in the mid 1980s with Dr. Theo Seiler using a metal masking template and the excimer laser to create corneal arcuate incisions, followed by Dr. Marguerite McDonald’s photorefractive keratectomy (PRK), and Dr. Lucio Buratto substituted the excimer for the cryolathe by ablating the corneal cap posterior surface. Dr. Ioannis G. Pallikaris combined the ALK concept of a hinged corneal flap and ablation of the corneal stromal bed, which he labeled LASIK, followed by the introduction of LASEK.

LASIK rapidly became the procedure of choice over PRK surface ablation, even though it was more costly, complicated, and added the risks of microkeratome complications, because surgeons were looking for ways to reduce the patient’s postsurgical pain and a more rapid improvement in vision, the so-called “wow phenomena”. It also became clinically evident that LASIK decreased the use of topical steroids, antibiotics, nonsteroidal anti-inflammatory drugs (NSAIDS), haze formation, and postoperative care.

The LASIK advantages were obvious, but it became apparent that many patients were not good LASIK candidates. LASIK contraindications included a multitude of factors, such as too steep or too flat corneas, very low or high refractive errors, thin corneas, epithelial dystrophies, and the fear of some surgeons and patients concerning the use of the microkeratome to “cut the cornea.”

Thus, new evolution stages occurred as surgeons wanted a less invasive surgery than LASIK, but more comfortable procedure than PRK, which led to the development of LASEK.

As is common, when a new ophthalmic procedure goes through the normal transitional phases, terminology changes can occur, with several different terms applied to basically the same procedure, causing some confusion. Laser subepithelial keratomileusis is no exception.

The LASEK term has been used by Condon (2) and Vinciguerra (3). Pallikaris (4) described his “epi-LASIK technique”. Durrie (5) recommends advanced surface ablation for alcohol-assisted PRK and LASEK, and it is important to note the program title of the second international LASEK meeting in Cleveland, Ohio, May 2003, was “Second International Congress on LASEK and Advanced Surface Ablation.” In our office we now use advanced laser surface ablation (ALS A) for LASEK and transepithelial or alcohol-assisted PRK (6). In this chapter, LASEK is used for the current specific procedure but we recommend ALSA, to avoid confusion with LASIK, for the general designation of the several surface ablation techniques.

Azar’s and Camellin’s LASEK procedure which combine the retention of an epithelial flap after surface ablation with the potential advantages of less pain with more rapid visual recovery than PRK and decreased potential LASIK flap complications, make it a reasonable alternative, especially for non-LASIK candidates. Because of these potential advantages we began LASEK in 2001, when it was just on the horizon, and in the past 600 laser vision correction cases performed, approximately 50% were LASEK and 50% LASIK. Several ophthalmologists, e.g., Camellin (7), Yee (7), Claringbold (8), and Gayton (9) perform only LASEK. Currently, LASEK may be approaching “high noon,” but we cannot predict where the sun will set.

It became obvious after a few LASEK cases that alcohol application time varied significantly, as did epithelial devitalization, flap shredding, post-operation inflammation, patient discomfort, and visual recovery. Therefore, we began looking for techniques that would facilitate the formation of better epithelial flaps with or, hopefully, without alcohol application.

The first idea was a form of “fluidic dissection” such as hydrodissection of the lens with balanced salt solution (BSS) during cataract extraction. A more earnest pursuit of a hydrodissection technique came after conversations with Dr. Patrick Condon of Ireland, who presented at the European Cataract and Refractive Surgery Congress 2000 his procedure of replacing the epithelial flap followed by irrigation with BSS under the flap, which we, with his approval, have applied the terms “subepithelial hydrofloatation and cleaning.”

At the time we were developing the fluidic epithelial dissection techniques, a literature search revealed no articles or reports of any similar techniques. The original LASEK epithelial flap (LEF) hydrodissection (HD) technique was performed, after the epithelium was scored and alcohol applied, by injecting BSS subepithelially through a Slade LASIK cannula with the tip placed under the loosened epithelial edge. The technique was successful with the very first case and since has been used in a variety of methods in more than 1000 LASEK procedures.

This is the first published formal report on hydroviscodissection, but we first introduced LASEK epithelial flap hydrodissection (10) (LEFHD) at the International

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Society of Refractive Surgery, 2001. Later, McDonald introduced gel-assisted LASIK (11) using GenTeal Gel (Hydroxypropyl methylcellulose 0.3% plus Carbopol 980; Ciba Vision) at the American Academy of Ophthalmology, 2001, and Langerman (12) introduced viscodissection (VD) with Celluvisc (carboxymethyl cellulose 1%; Allergan) at the First International LASEK Congress 2002.

Hydroviscodissection Mediae and Terminology

As a result of the successful hydrodissection technique with BSS, we evaluated several mediae, specifically BSS, air, GenTeal, and GenTeal Gel, as dissection mediae and later reported on the safety and efficacy of all of these mediae for hydrodissection and viscodissection (10,13–17).

We originally designated BSS and GenTeal (hydroxypropyl methylcellusose 0.2%; Ciba Vision) as hydrodissection (HD) mediae and GenTeal Gel as a viscodissecting (VD) mediae (13–16). After the introduction of Celluvisc by Langerman, GenTeal and GenTeal Gel by Rashid, and Laservisc (0.25% hyaluronate; Laservisc, Germany) by Rau (18) as viscodissecting media, we now recommend the use of the terminology hydrodissection when BSS is used and viscodissection with more viscous fluidic mediae, including Gen-Teal, Celluvisc, GenTeal Gel, and Laservisc (20–22). Hydroviscodissection indicates the general surgical manuevers, not the media.

BSS is available, cost-effective, and easy to handle. BSS hydrodissection characteristically causes slight to considerable epithelial ballooning and drains quickly, yet makes flap retraction easier and less traumatic (Fig. 1) (10,13).

Air proved to be a poor dissecting media, although air bubbles that occur and remain under the flap after hydroviscodissection do give a “ball-bearing effect,” prevent epithelial settling, and make flap retraction very easy (13–19).

GenTeal proved to be an excellent fluidic dissecting media, characteristically causing significant epithelial stretching and ballooning, with longer retention keeping the epithelium elevated, and greatly facilitates flap retraction and replacement while decreasing flap shredding (Fig. 2) (14–17,19–22).

GenTeal Gel is very effective in dissecting and maintaining epithelial ballooning, making epithelial retraction the easiest, as the flap literally floats over the retained Gel, but it costs more, is not as easy to use, plus it requires more surgical time and preablation cleanup (Fig. 3) (15–17,19–22).

Overall, BSS hydrodissection and GenTeal or GenTeal Gel viscodissection all proved to be safe (10,11,13–17,19–22), efficacious mediae techniques for fluidic epithelial dissection, as are Celluvisc (12) and Laservisc (18), with the latter being more expensive.

Originally, BSS hydrodissection was rated as the best epithelial detachment modality (13–15) because of cost, availability, ease of handling characteristics at surgery, and other criteria. We now rate GenTeal Viscodissection as the best overall epithelial dissection media technique, offering the advantages of both BSS hydrodissection and GenTeal Gel viscodissection with minimal disadvantages (Table 1) (17–20,22).

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repositioning were easier, more stable, and “the excellent transparence of the flap is cause for the faster optical recovery in comparison to the classical technique” of Camellin.

Figure 3 GenTeal Gel viscodissection characteristics with and without alcohol. Epithelial stretching and ballooning with long retention greatly facilitates flap retraction but requires more surgery and preablation clean-up time.

Table 1. Fluidic Dissecting Media Comparison for Hydrodissection (HD) vs. Viscodissection (VD).

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Figure 5 Rashid LASEK hydrodissection and viscodissection cannula (RHEIN).

and facial skin wrinkling” as increased risk factors for epithelial defects with LASIK. This inherent “epithelial defect risk” makes hydroviscodissection easier, with or without alcohol, in these patients, making them excellent LASEK candidates, thus avoiding the multiple complications caused by LASIK induced epithelial defects (10,13,15–17,21). A clinical observation is that many of these individuals have rosacea and/or dry eye syndrome, plus often a history of hives. We closely examine the facial skin before surgery and perform punctal occlusion on these patients. We now occlude all four puncta, either with four Herrick collagen implants (Lacrimedics, Inc.) or soft PLUG-SA (Oasis Medical Inc.) or two permanent plugs and two collagen implants, on all laser vision correction patients.

LASEK Cannula

Initially, there were no specific LASEK cannula available, so the Slade LASIK cannula was the first to be evaluated and although successful, had the disadvantage of the epithelium catching on the cannula anterior to the port and the fluid initially goes over rather than under the epithelium if the flap edge is not loosened and elevated properly. Realizing a specific LASEK cannula with a flat smooth bottom, a tapered anterior lip with a curved superior aspect, and the port located very near the tip was needed, we collaborated with Rhien Medical and designed the Rashid-LASEK cannula (19,20,22) incorporating the aforementioned specifications plus a rectangular horizontal port near the tip. The author has no financial interest in this product.

Figure 6 Seibel LASIK cannula: one direction, multiple side ports (left shown) (RHEIN).

Currently, this LASEK cannula and similar variations with a round front port nearer the tip proved to be the most successful to initiate and complete hydro or viscodissection. It also is very effective in flushing out debris adherent to a LASIK flap. Several other cannula were evaluated, including one directional, multiple side port cannulae, e.g., the Seibel (Fig. 6), and McDonald McLASEK (Fig. 7), the two directional Güell (Fig. 8), and the three directional Burratto cannula (Fig. 9), and all proved ineffective in initiating hydro or viscodissection (19,20,22) because of the shape of the tip and the location of the ports.

A two-cannulae technique using a front port cannula, e.g., the Slade LASIK or Rashid LASEK cannula, to initiate hydro or viscodissection, followed by a one-directional multiple port, e.g., Seibel, or a multi-directional cannula, e.g., Guell or Burrato, can be effective in detaching the epithelial flap (19,20,22). The advantage of the multiple one directional side port cannulae is that once hydro or viscodissection has been initiated, they can be passed into the created channel and with gentle downward pressure along the entire curved cannula shaft plus a slight sweeping motion, like a water broom, to complete the hydroviscodissection procedure (19,20,22).

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Figure 7 McDonald McLasek cannula: one direction, multiple side ports (left shown. (MASTEL).

Figure 8 Güell LASIK cannula: two direction, multiple ports (RHEIN).

Figure 9 Burrato LASIK cannula: multi-directional ports (RHEIN).

Keys to Successful Fluidic Dissection

The keys to successful fluidic dissection, whether hydro or viscodissection, are a loosened epithelium, especially at the edge where it is more adherent; placing the cannula port under the flap edge before fluid delivery; and using a fluidic dissection media that is cost-effective, available, and easy for the assistants and surgeons to use during surgery.

Techniques for Loosening Epithelium

Techniques to loosen the epithelium and decrease or eliminate alcohol application before fluidic dissection are:

1.The use of xylocaine gel 2% for 15 to 30 minutes preoperatively, which initiates anesthesia, lubricates, and loosens the epithelium. A moist Merocel sponge is used to gently massage and remove the excess gel and further loosen the epithelium before scoring the epithelium (13–17,19–22). Berstein (24) uses a similar concept, painting the conjunctiva and cornea for 30 seconds with a proparacaine-soaked Merocel sponge to enhance anesthesia and mechanically loosen the epithelium.

2.Enhance the epithelial incision with scissors or a bent needle which allows alcohol, if used, to seep under the edges, further loosening the epithelial edge attachments, but may give a ragged edge. A disposable trephine gives a more defined edge and is easier to enhance.

Local Alcohol Application

3D. Local application using a soaked long strip of Merocel placed just over the epithelial incision (Fig. 12) (20,22,25).

3E. Merocel spear placed just over the epithelial area where hydroviscodissection is to be initiated, greatly limiting the alcohol applied area.

Figure 11 Melki M-LASEK alcohol well (ASICO). Peripheral well confines alcohol over epithellal incision. Central well used for minimal application if needed.

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Figure 12 Local alcohol application on merocel sponge strip over epithelial incision, sparing central area.

Alcohol application time varies from 20 to 60 seconds, depending on the surgeon and patient’s epithelial response, especially of the fellow eye.

4.Suction epithelial detachment (SED) performed by applying a contact lens suction removal device with a rotating motion (Fig. 13) (19–22). Suction epithelial detachment can be attempted before and/or after alcohol application. If the epithelial edge is lifted and folded on itself, it is possible to tear the flap so one should make sure the flap edges are flat before applying the device and initiating the rotating movements. A central flap tear is rare, and we have only seen a few. It is important to also perform SED over the hinge site, making epithelial dissection in this area easier and preventing shredding of the hinge.

5.Lifting the flap edge with an instrument, e.g., the Machat spatula (ASICO), Brown hoe (Rhein), or bent needle, makes it easier to slip the cannula tip, including the port, under the flap before initiating hydroviscodissection.

6.We have occasionally used the Easy-Freeze (16) cryo-applicator (Eurocrystal, Italy). The concept is to enhance anesthesia and prevent haze. This is a heavy stainless steel instrument, shaped like a top hat with a large curved bottom and a small top end. The instrument is frozen, removed from freezer, and placed immediately on the intact cornea for 30 to 60 seconds. An ice ball is often seen and may also help to loosen the epithelium. The small end is placed on the stromal bed after ablation. No specific clinical studies have been performed and further evaluation would be interesting. One disadvantage is it takes a long time to freeze and multiple instruments might be required if used routinely.

7.McDonald (11) applies sodium chloride 5 % o ver the entire cornea for 10 seconds “which stiffens and loosens the epithelial cells without killing them.”

All of these techniques may be tried before application of alcohol, especially general application, to ascertain whether alcohol is necessary to further loosen the epithelium. Many epithelial flaps can be dissected without alcohol, although it may take a lot of

Figure 13 Figure 13. Suction epithelial detachment (SED) with contact lens suction device. (Note detached epithelium at arrow) (Rashid).

patience and increased time. There is no question that alcohol application makes flap retraction with or without hydroviscodissection easier and faster. McDonald (11) has investigated incorporating ultrasound and sonic energy to evaluate their efficacy in loosening the epithelium.

Epithelial Flap Manipulation Techniques

Even with all of these techniques, some flaps are initially difficult to retract and often shredding occurs at the edge and the hinge. It is more effective to detach, loosen, and retract the flap edges in a U-shaped fashion along the incision rather than going straight across during flap retraction. We stress taking care at the hinge area, because one can make a beautiful, perfect flap only to have it shred or torn from the hinge where the epithelium is more adherent. If the flap hinge should completely tear, just fold the flap

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back gently in the superior fornix, cover it with GenTeal Gel, and when irrigating the cornea be careful not to float it away, then replace it as a free flap.

Replacing the flap is performed using either a wet technique with a one-direction irrigating cannula, e.g., Seibel, or a very moist Merocel sponge, or a dry technique with a spatula. Replacement is easier if the hinge is totally intact. The flap will adhere quicker with the dry replacement technique. Air can be used to dry the flap.

If the flap is irregular, too adherent to position properly, or has subepithelial debris, one can use Condon’s (2) “subepithelial hydrofloatation and cleaning” irrigation technique with any appropriate cannula and BSS and reposition the flap.

The epithelial flap is usually stretched and larger than the defect and some surgeons will trim the edges with scissors, removing the shredded edges, and try to place the epithelial edges edge to edge. There may be large defects and particularly if central, one can place the central edges together and leave the peripheral edges unopposed.

At this point, one drop of proparacaine followed by several drops of sodium chloride 5% solution is used to increase epithelial flap adherence and reduce stromal edema before placing a nonionic low water content bandage soft contact lens (BSCL), usually a B&L S of 66, Optima FW, or 2-Week Lens. Petelin et al. (26) and Durrie (27) have reported that a nonionic low water (BSCL) content avoids the “tight lens syndrome” seen at 2 to 3 days postoperatively. McDonald previously used a Protek BSCL (28), which is no longer available, but the CSI lens, also by CIBA, has therapeutic Food and Drug Administration (FDA) approval and can be used as a BSCL. If the BSCL comes out, it will usually, but not always, remove the epithelial flap. Patients are given a new contact lens kit and advised to clean and, if possible, replace the BSCL.

Epithelial Sanctity: Perfect vs. Partial vs. No Flap; Viable vs. Nonviable Flap

Several important factors causing a resurgence of ALSA are that surface ablation avoids flap complications, is less costly, gives better wavefront custom results, induces less aberrations associated with LASIK, and now there are better methods of controlling postoperative pain and dryness.

The first question is will LASEK or PRK, alcohol-assisted or not, be the best ALSA procedure? Thus, the sanctity of the flap becomes more important. Durrie et al. (29) and others have reported the fact that ALSA induces less aberrations, and MacRae (30) reported increased spherical aberrations with LASIK myopic corrections. Schallhorn (31) reported “distinctly different” and greater higher order aberrations with LASIK over “conventional PRK.” Most past presentations, e.g., Durrie (29), Rau (32), Rashid (10), and others have reported less patient discomfort, faster visual recovery, and equal longterm visual results with LASEK vs. PRK. However, Litwak et al. (33), and earlier, Garcia de-Quevedo (34) presented data “that PRK eyes felt less discomfort and had better vision than LASEK eyes” and “healed faster.”

The next question, “Should we save the epithelium or scrape it off?” was literally the topic of the round table discussion at the Second International Congress on LASEK and Advanced Surface Ablation, Cleveland, Ohio, May 2003. There were diverse opinions, e.g., Yee (35) advocated salvaging as much of the epithelial flap as possible while others felt any flap that is “not perfect” should be removed to promote faster healing. Moore

(22) personally advised the author that some reported up to a 50% removal rate of imperfect flaps. In more than 900 LASEK procedures, we have removed less than 15 epithelial flaps, and always try to retain as much epithelium as possible (36).

If a perfect LASEK epithelial flap could be made without alcohol or with minimal use of alcohol, it would be advantageous. Alcohol is a known contributing cause of epithelial cell death, toxicity, plus conjunctival and general inflammation post-operative. If the corneal flap was more viable would patient comfort, epithelial healing, and visual restoration be improved? Durrie et al. (5) reported that epithelial healing is as good in alcohol-assisted advanced laser surface ablation with removal of the flap and has basically little difference with LASEK in healing, visual recovery, and patient comfort.

So, there is still some controversy whether a perfect vs. nonperfect vs. no flap, or a viable flap vs. a nonviable flap makes a difference in patient comfort, faster epithelial healing, and visual recovery, but most surgeons agree there is minimal difference in longterm vision. Is it possible that applying alcohol for 60 to 90 seconds to create a more uniform epithelial flap easier and using the devitalized epithelial flap only as a protective “patch” might promote more even healing, increased comfort, and be as effective as a 25% or more viable flap? These questions will continue to be debated, and rightly so!

LASEK With Mitomycin-C: Haze Prevention and Treatment:

The use of mitomycin-C remains variable. There are many earlier reports, e.g., by Carones (37), Majmudar, Epstein et al (38) and Rashid (39) all at ASCRS 2000, and Azar (40), of excellent results in treating, reducing, or preventing postoperative corneal haze without major complications with the use of mitomycin, especially in complicated and high ablation cases. Some, e.g., Aldave (41), Hashemi (42), Rashid (16,17,19–22,43), and others, use mitomycin-C prophylactically with surface ablation to prevent corneal haze and all reported good results and no specific related complications. This is probably because of the fact that the mitomycin is placed on the avascular cornea. Most ophthalmologists are aware of the potential scleral melting syndrome seen postoperatively with pterygium or glaucoma filtering procedures in which mitomycin is placed over vascularized sclera.

As more people are using mitomycin C 0.02% with an application time ranging from 30 seconds to 2 minutes to prevent corneal haze after surface ablation, it is important to protect the peripheral limbal vessels, epithelium, and stem cells. We recommend the use of a GenTeal Gel Barrier, which is placed 360 degrees over the limbal epithelium, to confine mitomycin only over the ablated stroma while protecting vessels and lubricating the limbal epithelium and stem cells (Fig. 14 and Fig. 15) (17,19–22).

Our primary LASEK hydroviscodissection protocol is depicted in Figure 16: (steps 1– 12), although a bladeless microkeratome technique is currently being evaluated.

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Figure 14 GenTeal Gel Barrier (Rashid) placed 360 degrees over peripheral epithelium and limbus to confine mitomycin-C over ablated stroma while protecting and lubricating limbal vessels, epithelium, and stem cells.

Figure 15 Merocel sponge with mitomycin-C (0.02%) contained within a GenTeal Gel Barrier.

Bladeless Microkeratome Flap Retraction Technique

A “perfect” epithelial flap dissection is not always possible. Some downward pressure must be exerted by the instrument on the cornea anterior to the epithelial edge during dissection. Hoes dissect a small narrow area and spatulae require more downward pressure to flatten the cornea for the one sweep technique. Both techniques can cause flap button-holes or shredding, especially if hydroviscodissection is not performed, or the epithelium is more adherent.

In ALSA cases, we recently began using a bladeless microkeratome to retract the epithelial flap after hydroviscodissection, which is necessary, has been completed. In this method, the flap is prepared by trephination, alcohol application if necessary, GenTeal viscodissection followed by application of the Möria (−1) vacuum ring, and the manual Carriazo-Barraquer microkeratome without a blade is passed until the front edge of the

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head reaches the inside ring edge, retracting the flap to the superior hinge (6). Usually and depending on the extent of hydroviscodissection, two types of flaps are produced: a one-sheet flap with a superior hinge (Fig. 17A−17C), or a central epithelial opening over

Figure 16 (LASEK) ALSA with hydrodissection or viscodissection protocol: Step 1. Score epithelium with Sloan trephine (KATENA). Step 2. Enhance incision with scissors or needle. Step 3. Apply 20% alcohol 30 to 60 seconds *optional. Step 4. Remove alcohol with Merocel sponge. Step 5. Suction epithelial detachment (SED). Rashid. Step 6. HD or VD with BSS, GenTeal, or GenTeal Gel.

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Figure 17 (A) Bladeless moria manual C-B microkeratome in place after GenTeal viscodissection and preadvancement. (B) Flap retraction after MK pass and return (Note flap at hinge superiorly at white arrow and mk return at yellow arrow) (C) Epithelial flap retracted superiorly, preablation.

the epithelium most elevated by retained GenTeal, creating a superior and inferior flap. When a central opening occurs, two opposite linear relaxing incisions may be necessary in the more peripheral points of the opening, thus converting it to a “butterfly” type of flap.

Flap shredding can occur and is usually at the peripheral lower flap edge or at the hinge. There is usually enough residual superior flap to cover all or most of the stromal bed. Hinge shredding can be prevented by not pushing the front edge of the microkeratome head past the suction ring inside edge.

The disadvantage to this technique is suction application and the resultant subconjunctival hemorrhages. Naphcon-A (naphazoline-0.025%; pheniramine-0.3%, ALCON is used as is in LASIK cases, to decrease these hemorrhages.

In two attempted cases without GenTeal viscodissection the microkeratome passed over the epithelium, but both were successfully completely with viscodissection.

Further refinement and evaluation of this technique has been curtailed as moria has developed an epithelial microkeratome but it is not yet FDA approved.

SUMMARY

LASEK epithelial flap hydrodissection and viscodissection are safe, effective, and efficient LASEK maneuvers but require increased time, cost, and surgical skills. BSS for hydrodis-section and GenTeal, GenTeal Gel, Celluvisc, or Laservisc for viscodissection are all effective and safe laser epithelial flap dissecting media techniques. Currently, we rate GenTeal viscodissection as the number one choice of fluidic dissecting techniques because it combines the advantages of both BSS hydrodissection and GenTeal Gel viscodissection with minimal disadvantages.

Hydrodissection or viscodissection make flap retraction easier, less traumatic, decreases corneal and conjunctival drying, decreases alcohol application time, and may be performed without alcohol in many cases.

Hydrodissection or viscodissection techniques are adaptable to any surgeon’s LASEK protocol requiring only the media of choice, a syringe, and a front port cannula, e.g., the Rashid LASEK or Slade LASIK cannula, to initiate and complete epithelial detachment. A two cannula technique using an appropriate front port cannula to initiate hydroviscodissection followed by a cannula with multiple one-directional side ports, e.g., the Seibel, for completion, can be very effective.

Enhancing the epithelial incision before or even without alcohol application makes hydroviscodissection easier. Alcohol, although not necessary in every case, makes hydroviscodissection easier. Alcohol application with a Merocel sponge applied with pressure and movement may be more effective than using an alcohol well to loosen epithelium, may decrease alcohol time, and may be used in combination with the alcohol well (6).

Epithelial flap detachment with a contact lens suction cup or a Rashid LASEK Merocel Sponge (Ultracell Medical Technologies, Inc.) allows direct observation and identification of the loosened area. Easy-Freeze cryothermy may enhance epithelial detachment, as may sodium chloride 5%.

Complications seen are the same as LASEK in general, e.g., dry eyes, persistent epithelial defects, e.g., those lasting more than 14 days postoperative, which are most likely neurotrophic, and haze (10,16). The only specific hydroviscodissection complications seen have been flap puncture, tear, loss or iatrogenic removal, and conversion to PRK, and an occasional Bowman’s membrane abrasion, which cause no major complications (10,15,17).

Visual results are comparable with all three media and no specific alterations in one’s nomogram appears necessary but these should be monitored. It is interesting to note that alcohol is a drying agent and the fluidic dissecting media are wetting agents; yet, we have not altered our nomogram and feel this is because Bowman’s membrane is intact before the ablation and the different effects negate each other, although we have not seen a difference using fluidic dissecting media without alcohol.

One must be careful when using hydroviscodissection especially with BSS, because the fluid can potentially hit the laser optics and if so, can cause hot spots. One must be

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very careful and protect the optics. We recommend looking at the mirrors each day before initiating surgery.

If mitomycin-C is used, we recommend the use of the GenTeal Gel Barrier to contain the mitomycin and protect limbal vessels, epithelium, and stem cells. Some surgeons decrease their nomograms from 4% to 12%, depending on age and amount of ablation, when using mitomycin, because it may prevent normal healing regression.

Lastly, Pallikaris (44) has developed his subepithelial separator, Caniazo (45) has reported his pendular LASIK microkeratome is capable of creating a subepithelial flap, plus Moria (France) and Gebauer (Germany) companies have developed subepithelial microkeratome, all of which eliminate the use of alcohol. If in the long term, these instruments are proven efficient, effective and are available, they may make these hydro viscodis-section techniques outdated. All the techniques described are not FDA approved and the author has no financial conflicts but may still be more cost-effective for lowvolume surgeons who cannot justify the investment in another microkeratome.

REFERENCES

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5.Durrie DS, Petelin PM Jr. LASEK using the LADAR Vision platform. ASCRS, Philadelphia, PA, June 1–5, 2002: Paper: Abstract 311:p. 79.

6.Rashid RC. New LASEK Techniques: Rashid LASEK Sticksponge and Bladeless Microkeratome Flap Retraction. Third International Congress on LASIK and Epi-LASIK and Advanced Surface Ablation. Houston, TX, March 19–20, 2004: Paper.

7.Personal communication with Camellin M and Yee R.

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11.Burrill A. Gel-assisted LASEK. Cataract Refract Surg Today 2002:57–58.

12.Langerman DW. LASEK A Visco-dissection Technique. First International LASEK Congress, Houston, TX, March 22–23, 2002: Paper.

13.Rashid RC. Hydrodissection of LASEK Epithelial Flap: A new surgical maneuver. First International LASEK Congress Houston, TX, Mar 22–23, 2002: Paper.

14.Rashid RC. LASEK Enhancement Challenges. International Society of Refractive Surgery, Fall Refract Cat Symp, 2002: Paper: Abstract: p. 43.

15.Rashid RC, Moore GS. LASEK Epithelial Flap Hydrodissection vs. Viscodissection: A media technique comparison. International Society of Refractive Surgery, 2002: Poster Abstracts: p. 78.

16.Rashid RC. LASEK: Review of Complications, Epithelial Flap Hydrodissection and Mitomycin-C. ASCRS, Philadelphia, PA, June 1–5, 2002: Paper: Abstract 313:p. 79.

17.Rashid RC, Moore GS. LASEK Epithelial Flap Hydrodissection vs. Viscodissection: A media technique comparison. XXIV Pan-Am Congress of Ophthalmology, San Juan, Puerto Rico, Mar 28–Apr 1, 2003:Poster: pp. 1089: Abstract: Program p. 92.

18.Rau M. First results of a LASEK viscodissection technique. ASCRS, San Francisco, CA, Apr 12–16, 2003; Paper: Abstract 289:p. 75.

19.Rashid RC. New LASEK Surgical Techniques. XXIV Pan-Am Congress of Ophthalmology, San Juan, Puerto Rico, Mar 28–Apr 1, 2003; Paper: Abstract: Program p. 92.

20.Rashid RC. LASEK Epithelial Flap Hydro-viscodissection Instruments: Comparison of cannulae. ASCRS, 2003; Paper: Abstract 290:p. 75.

21.Rashid RC, Moore GS. New LASEK techniques: Suction Epithelial Detachment; HydroViscodissection; and Mitomycin—GenTeal Gel Barrier. ASCRS, San Francisco, CA, Apr 12– 16, 2003; Poster: 151: Abstract: ASCRS Program p. 135.

22.Moore GS, Rashid RC. New LASEK techniques and instruments. Second International Congress LASEK, 2003; Paper.

23.Bashour M. Risk factors for epithelial defictin LASEK. ASCRS, San Diego, CA, Apr 28–May 2, 2001; Paper: Abstract 90:p. 23.

24.Berstein RM. Proparacaine “Painting” to facilitate LASEK flap epithelial peeling. ASCRS, San Francisco, CA, Apr 12–16, 2003; Paper: Abstract 85:p. 23.

25.Melki S. M-LASEK: Minimize alcohol, Maximize survival. ASCRS, San Francisco, CA, Apr 28–May 2, 2003; Paper: Abstract 284:p. 74.

26.Petelin P, Durrie DS, Husiman EE. Laser Assisted Subepithelial Keratectomy (LASEK). International Society Refractive Surgeons Fall Refractive Symposium, New Orleans, LA, Nov 8–10, 2001; Paper: Abstract: p. 52.

27.Durrie DS. Selecting a Contact Lens for LASIK. Refractive Eyecare For Ophthalmologist; 2002; 6(4).

28.Bourque L, McDonald M, Salib G, Planchard L, Culotta T, Smolek M, Klyce S.. ASCRS, San Francisco, CA, Apr 12–16, 2003; Paper: Abstract 291:p. 75.

29.Durrie DS, Stahl JE, Collins MJ. Comparison of LASIK and LASEK for 1 to 7D of Myopia with up to 3D of Astigmatism. ASCRS, San Diego, CA, Apr 28–May 2, 2001: Paper: Abstract 9:p. 3.

30.MacRae S, Cox I. Effect of Customized Pupil Size, Optical Zone Size, and Refractive Error on the magnitude of Spherical Aberration Induced by LASIK. ASCRS, San Francisco, CA, April 12–16, 2003; Paper: Abstract 192:p. 50.

31.Schallhorn SC. Differences in Aberrations Induced by PRK and LASIK. ASCRS, San Francisco, CA, April 12–16, 2003; Paper: Abstract 194:p. 51.

32.Rau M. First Results of LASEK for the Correction of Myopia. International Society of Refractive Surgery Fall Symposium, New Orleans, LA, Nov 8–10, 2001; Paper: Abstract: p. 52.

33.Litwak S, Chayet A, Missiroli F, Garcia-de-Quevedo V, Robledo N. . International Society of Refractive Surgery Fall Symposium, New Orleans, LA, Nov 8–10, 2001; Paper: Abstract p. 51.

34.Garcia-de-Quevedo V. Clinical Comparison of LASEK and PRK. First International LASEK Congress, Houston, TX, March 22–23, 2002; Paper.

35.Yee R. “Should we save the epithelial or scrape it off?”. Second International Congress LASEK, Cleveland, OH, May 30–31, 2003; Round table discussion.

36.Rashid RC. LASEK conversions to PRK of surgery. Third International Congress on LASEK and EPI-LASIK, and Advanced Surface Ablation. Houston, TX, March 19–20, 2004; Paper.

37.Carones F. Treating Haze and Regression by Scraping and Mitomycin-C. ASCRS, Boston, Mass, May 20–24, 2000; Paper: Abstract: 720:p. 182.

38.Majmudar PA, Epstein RJ, et al. Topical Mitomycin-C for Corneal Haze after Refractive Surgery. ASCRS, Boston, Mass, May 20–24, 2000; Paper: Abstract 721:p. 182.

39.Rashid RC. Mitomycin-C uses in PRK. ASCRS, Boston, Mass, May 20–24, 2000; Paper: Abstract: 723:p. 182.

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40.Shahinian L, Claringbold TV, Azar DT, Camellin M, Vinciguerra P. LASEK (Laser-assisted Subepithelial Keratectomy). ASCRS, Philadelphia, PA, June 1–5, 2002. Course 2 207: Abstract Program p. 86.

41.Piantoni G, McLeod SD, Abbott RL, Aldave AJ. LASIK Complications: Prevention and Management. XXIV Pan-Am Congress of Ophthalmology, San Juan, Puerto Rico, March 28– Apr 1, 2003; Course TW0432: Abstract: p. 53.

42.Hashemi H, Takeri MR, Gotouhi A. Effect of Prophylactic Application of Mitomycin-C in PRK for High Myopic. ASCRS, San Francisco, CA, Apr 12–16, 2003; Paper: Abstract 13: p. 4 and personal communication.

43.Rashid RC. Mitomycin-C uses in PRK. ASCRS, Boston, MA, May 20–24, 2000; Paper: Abstract: 723:p. 182.

44.Pallikaris I. Epi-Keratome. International Society of Refractive Surgery, Orlando, FL, Oct 18– 19, 2002; Paper: Abstract: p. 44.

45.Carriazo CC. LASIK and LASEK pendular microkeratome. ASCRS, San Francisco, CA, Apr 12–16, 2003; Paper: Abstract 293:p. 76.

10

Surface Ablation Without Alcohol: Gel- Assisted LASEK and Epi-LASIK using

Epilift System

Puwat Charukamnoetkanok, MD and Dimitri T.Azar, MD

Massachusetts Eye and Ear Infirmary, Schepens Eye Research Institute

Harvard Medical School

Boston, MA

Manual epithelial debridement was found to produce scratches and nicking in the Bowman’s layer and to leave variable amounts of epithelium (1,2). Chemical agents like 0.5% proparacaine iodine, cocaine, alkali n-heptanol, and ethanol have been used to remove the corneal epithelium in experimental studies (3,4). Currently, 18% to 20% ethanol is commonly used in laser subepithelial keratomileusis (LASEK). However, it is potentially toxic to the corneal tissue. The use of 100% ethanol for 2 minutes on rabbit corneas lead to a significant decrease in stromal keratocytes after 24 hours (4). Similarly, when using 70% isopropyl alcohol for 2 minutes for epithelium removal in rabbit eyes, Agrawal et al. found an increased inflammatory response and damaging effect on keratocytes (5). Helena et al. observed increased keratocyte loss but decreased inflammation after using 50% ethanol for 1 minute compared to mechanical debridement

(6). Indeed, the toxic effect of alcohol on epithelial cells has been used for therapeutic purposes. For example, 50% ethanol was reported in the treatment of progressive or recurrent epithelial in-growth after laser in situ keratomileusis (LASIK) (7).

Despite superior results to those using mechanical scraping, the reliability on alcohol for the manipulation of the corneal epithelial in LASEK is one of its major drawbacks. The search for nontoxic alternatives to alcohol is ongoing to improve the safety, efficacy, and reproducibility of the methods to separate the corneal epithelium from the stroma. Promising candidates include less toxic substances such as methylcellulose gel or water and mechanical devices similar to LASIK microkeratomes (the Epilift system for EpiLASIK surgery described below and the Pallikaris separator described in chapter 12).

GEL-ASSISTED LASEK

The alcohol-free McDonald technique uses LASIK-microkeratome suction and a methylcellulose gel to create the epithelial sheet (Fig. 1). A curved cannula (Mastel Precision, Rapid City, SD) with fine holes along the side through which GenTeal Gel (hydroxypropyl methylcellulose 0.3%; Novartis Ophthalmics, Duluth, GA) can simultaneously emanate is used. Because methylcellulose gel unlike alcohol does not

LASEK, PRK, and excimer laser stromal surface ablation 128

stiffen the epithelial cells, metallic instruments should never touch the epithelium. Instead, the cells are stripped using suction and manipulated on a cloud of gel.

Figure 1 McDonald alcohol-less technique. (From Taneri S, Zieske JD, Azar DT. Evolution, Techniques, Clinical Outcomes, and Pathophysiology of LASEK: Review of the Literature. Surv Ophthalmol November-December 2004 in press.)

In the procedure, generous amounts of GenTeal Gel are applied to the corneal surface to keep the epithelium in good condition. A rounded cataract blade is used to make a small linear abrasion in the far periphery of the cornea. Ten drops of NaCl 5% are added for 10 seconds to slightly stiffen the epithelium. The suction ring is positioned on the cornea. While the suction is on, a LASEK spatula is slipped through the 1-mm or 2-mm linear abrasion. Using that hole as a fulcrum, a spatulating motion is made and the epithelium stripped off. After a maximum of 30 seconds suction time the dedicated curved cannula is slipped under the epithelium and GenTeal Gel is blown out to dome-up the epithelium. Finally, the raised epithelium is bisected with Vannas scissors, creating two halves. After parting the two sides, the surgeon uses a wet Weck-cel sponge to remove the gel from Bowman’s layer and performs the ablation. After ablation, the surgeon again applies GenTeal Gel, reposts the epithelial sheet to its original position, and places a bandage contact lens (8).

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the cleavage plane to be above Bowman’s layer (C). External photography of the cornea 1 day (D) and 2 days (E) after surgery illustrate the rapid readhesion of the epithelial flap to the ablated stromal bed. (Modified from VisiJet with permission).

Surface Ablation without Alcohol

The success of the surgical technique using the EpiLift system depends on 4 factors: the applanator, the EpiLift, parameter control, and the relatively short learning curve. The applanator flattens the epithelium at a fixed distance from the point of separation and provides tissue alignment for cleaving. The radius of curvature of the EpiLift allows for atraumatic cleaving. The epithelial flap provides a natural contact bandage lens and acts as a barrier to help prevent haze. Use of a low vacuum suction ring and controlled transition

Figure 3 Prior to surgery, the microkeratome head is attached to the suction ring (A, green arrow) outside the eye. Diagramatic illustration of the mechanism of EpiLift showing the applanator and separator with the angled blade design (B) as the epithelium is lifted. The cleavage plane occurs between the lamina densa and Bowman’s layer. (Modified from VisiJet with permission).

speed and low oscillation rate across the path of separation allow for gentle tissue cleavage. The learning curve is relatively short because the separator system operates similar to existing mechanical microkeratomes and is set up prior to placement on the cornea.

Potential advantages of Epi-LASIK in wavefront-guided ablations still remain speculative. Achieving the optimal treatment dose can be hampered by patient subjectivity in establishing an accurate refraction. New wavefront technology will be able to obtain objective refractive data and may decrease the need for re-treatment in all types of laser corrective surgery (10).

Many investigators express their belief that LASEK may become the procedure of choice in wavefront-guided customized ablations because the benefit of these complex ablations may not be negated by variable iatrogenic aberrations because of a microkeratome-created stromal flap (11–14). However, the greater wound healing response in LASEK patients compared to Epi-LASIK patients may also mask the fine contours provided by wavefront-guided ablations and cause significant aberrations itself.

Additional study of the biochemical and histopathological causes of the healing response may lead to the development of a flap-making solution superior to the ethyl alcohol used mainly. A separation below the lamina densa would be desirable to further minimize haze formation and quicken visual recovery. Perhaps a better understanding of how the epithelium adheres to the ablated stroma would lead us to better techniques and ultimately outcomes.

REFERENCES

1.Campos M, Hertzog L, Wang XW, Fasano AP, McDonnell PJ. Corneal surface after deepithelialization using a sharp and a dull instrument. Ophthalmic Surg; 1992; 23:618–621.

2.Griffith M, Jackson WB, Lafontaine MD. Evaluation of current techniques of corneal epithelial removal in hyperopic photorefractive keratectomy. J Cataract Refract Surg; 1998; 24:1070– 1078.

3.Hirst LW, Kenyon KR, Fogle JA, Hanninen L, Stark WJ. Comparative studies of corneal surface injury in the monkey and rabbit. Arch Ophthalmol; 1981;99:1066–1073.

4.Campos M, Raman S, Lee M, McDonnell PJ. Keratocyte loss after different methods of deepithelialization. Ophthalmology; 1994; 101:890–894.

5.Agrawal VB, Hanuch OE, Bassage S, Aquavella JV. Alcohol versus mechanical epithelial debridement: effect on underlying cornea before excimer laser surgery. J Cataract Refract Surg; 1997; 23:1153–1159.

6.Helena MC, Filatov VV, Johnston WT. Effects of 50% ethanol and mechanical epithelial debridement on corneal structure before and after excimer photorefractive keratectomy. Cornea; 1997; 16:571–579.

7.Kim SY, Sah WJ, Lim YW, Hahn TW. Twenty percent alcohol toxicity on rabbit corneal epithelial cells: electron microscopic study. Cornea; 2002; 21:388–392.

8.Piechocki. T W. Alcohol-free LASEK procedure proves to effective in pilot study. Ocular Surgery News, Waikoloa, Hawaii, 2002.

9.Samalonis LB. LASEK techniques. EyeWorld; 2002; 7:31–32.

10.Sugar A, Rapuano CJ, Culbertson WW. Laser in situ keratomileusis for myopia and astigmatism: safety and efficacy: a report by the American Academy of Ophthalmology. Ophthalmology; 2002; 109:175–187.

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11.Rouweyha RM, Chuang AZ, Mitra S, Phillips CB, Yee RW. Laser epithelial keratomileusis for myopia with the autonomous laser. J Refract Surg; 2002; 18:217–224.

12.Vinciguerra P, Camesasca FI. Butterfly laser epithelial keratomileusis for myopia. J Refract Surg; 2002; 18:S371–S373.

13.Claringbold TV, 2nd. Laser-assisted subepithelial keratectomy for the correction of myopia. J Cataract Refract Surg; 2002; 28:18–22.

14.Azar DT AR. Laser Subepithelial Keratomileusis (LASEK). International Ophthalmological Clinics; 2002; 42:89–97.

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Figure 1 Subepithelial separator produced and distributed by Norwood Abbey Eyecare.

porcine eyes (Fig. 1). The particular characteristics of the device under patent are currently undergoing clinical trials in Europe and awaiting appropriate Food and Drug Administration (FDA) device approval in the United States.

Initial trials on porcine eyes have shown that the epithelial separation could be repeatedly achieved with the use of a proprietary oscillating blade without requiring any use of alcohol. Epithelial separation is achieved in a totally controlled way and most importantly, as shown by optical microscopy of the specimens, the separation is complete so that the reflection of the separated tissue require minimal surgical manipulations (Fig. 2).

Epi-LASIK: Surgical Procedure

The operative eye is anesthetized with topical tetracaine hydrochloride 0.5% eye drops, a sterile drape is applied, and a lid speculum is inserted. After copious irrigation with balanced salt solution using an anterior chamber cannula, the corneal epithelium is dried

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Figure 2 Light microscopy. Gross specimen of a porcine eye after the epithelial separation with the use of the subepithelial separator.

with the use of a merocel sponge, and the cornea is marked with a standard LASIK marker. The subepithelial separator is applied onto the operative eye and the suction is activated through a foot pedal.

The advance of the oscillating blade separates the epithelium leaving a 2- to 3-mm nasal hinge, the suction is released, and the device is removed from the eye. The epithelial sheet is reflected nasally with the use of a moistened merocel sponge to reveal the corneal stroma to be ablated.

After the application of the excimer laser ablation, the cornea is irrigated with balanced salt solution, and the epithelial sheet is positioned back in place using the straight part of the cannula under intermittent irrigation. The epithelial sheet is floated back in place using the previous corneal marks and is left to dry for 2 to 3 minutes. After that time, the epithelial sheet is well-adhered onto the corneal stroma. Anti-inflammatory and antibiotic eye drops are instilled and a therapeutic contact lens is applied onto the operative eye. Postoperative treatment includes anti-inflammatory eye drops (diclofenac sodium 0.1%; CIBA Vision Ophthalmics, Duluth, GA) for 2 days and combined eye drops of tobramycin dexamethasone (Tobradex, Alcon, Fort Worth, TX) until the removal of the lens on the day of reepithelization. After the removal of the lens fluorometholone (FML, Allergan, Irvine, CA), eye drops are prescribed in a tapered dose for 2 months.

Epi-LASIK: Initial Histopathological and Clinical Results

In an initial clinical study, we have used the final version of the sub epithelial separator in 21 eyes of 18 patients. All epithelial sheets were totally separated with regular borders and a diameter of approximately 8 to 9 mm. Ten patients received Epi-LASIK treatment in one eye and LASEK treatment in the fellow eye using two different alcohol solutions (15% and 20%, for 20 seconds). All epithelial sheets obtained either mechanically or after the use of alcohol were removed and the treatments were converted to photorefractive keratectomy (PRK). The specimens underwent transmission electron microscopy.

We found basement membrane discontinuities and basal cell fragmentation in specimens obtained with alcohol-assisted separation and confirmed that the alcoholassisted cleavage plane was within the basement membrane. In contrast, the basement membrane of the mechanically separated epithelial disks was mostly intact and showed

LASEK, PRK, and excimer laser stromal surface ablation 136

minimal cellular fragmentation indicating that in these cases the separation was not within but underneath the basement membrane (5) (Figs. 3 and 4).

In 11 additional eyes of eight patients, the epithelial sheet was left in place and the patients were followed-up for up to 3 months. Three of these patients received EpiLASIK treatment in both eyes whereas the rest received conventional PRK in the fellow eye (five patients). The mean re-epithelization time of the eyes that underwent EpiLASIK was 4.7 ±0.8 days. Biomicroscopy showed a transparent epithelial sheet on the first postoperative day (Fig. 5). During the postoperative course, the epithelial sheet showed some focal opacity at the borders of newly synthesized epithelium. On the day of re-epithelization, which was verified by negative fluorescein staining, the majority of Epi-LASIK-treated eyes showed a central epithelial raphe (Fig. 6).

One patient who was treated with Epi-LASIK in both eyes reported mild photophobia and tearing on the first 2 postoperative days; otherwise, no other patients reported any pain or other subjective symptom after Epi-LASIK.

Table 1 summarizes the subjective pain on the first postoperative day, the visual acuity on the day of re-epithelization, the time of re-epithelization, and the recorded haze 1 month after the treatment of the five myopic patients who underwent simultaneous PRK and Epi-LASIK treatments in each eye, respectively.

Figure 3 Transmission electron microscopy micrograph. Epithelial sheet obtained with the Epi-LASIK technique. Basal layer of the epithelial flap consisting of lamina lucida and lamina densa with occasional focal disruptions.

We recorded subjective pain in two PRK eyes and perhaps some haze results in the first month that could favor Epi-LASIK. There were no striking differences between the two modalities regarding the re-epithelization time and the visual acuity on the day of reepithelization.

Epi-LASIK 137

Because of the small number of eyes reported, we could not provide any conclusive results of comparing Epi-LASIK to conventional PRK. A larger series with adequate

Figure 4 Transmission electron microscopy micrograph. Epithelial sheet obtained with LASEK. Basal layer of epithelial flap. Epithelial cells of the flap with minimal trauma and edema. Cellular blebbing (formation of cytoplasmic fragments) was typical for this technique.

follow-up could provide some answers regarding the probable beneficial effect of the remaining epithelial sheet in terms of postoperative pain and the incidence of haze after the treatment.

Nomenclature

The term Epi-LASIK is based on the Greek word epipolis, which means superficial. Based on the use of a mechanical device to separate the epithelium and the entire basal lamina from Bowman’s and the underlying stroma, Epi-LASIK is a reasonable term. The term LASEK should be reserved for the use of alcohol-assisted epithelial separation. Both Epi-LASIK and LASEK, however, can be categorized as advanced surface ablations (ASA).

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Figure 5 Slit lamp photograph on the first postoperative day after EpiLASIK for myopia.

Table 1. Clinical Results of 5 Myopic Patients That Were Treated with Epi-LASIK (1 Eye) and PRK (Fellow Eye).

*Reported pain on the first postoperative day.

**Day of re-epithelization (negative fluorescein staining).

***Visual acuity on the day of re-epithelization.

****Recorded haze on the first postoperative month.

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Figure 6 Slit lamp photograph of an eye that underwent myopic correction with Epi-LASIK. Notice the central raphe of newly synthesized epithelium (postoperative day 4).

DISCUSSION

It is believed that the basement membrane provides the stability and support that keeps the epithelium intact, thus preserving the integrity of the entire corneal epithelium (6). Under this consideration, the adherence of the basement membrane to the basal layer of the epithelium must be significant for the viability of the epithelial disks, so we could assume that although alcohol dilutions are not reported toxic in the used concentrations, the cleavage plane of the mechanical epithelial disk separation may be considered superior. It will be important to determine if the epi-flap becomes adherent to the ablation surface or if the epi-flap acts only as a bandage until epithelial migration is complete. Studies by Fini et al. suggest the important role of the basal lamina in preventing activation of abnormal wound healing and haze (7). The basal lamina is variably present in LASEK and may account for the variability of clinical efficacy when compared to PRK (8,9). The wound healing time reported in this study suggests no difference in the time to complete healing between Epi-LASIK and LASEK (Table 1). In fact, the time to heal may actually be longer when compared to PRK. Future results of clinical studies

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may elucidate the probable beneficial effect of the remaining epithelial/basal lamina sheet on the corneal healing response after subepithelial treatments and perhaps the clinical importance of avoiding the use of alcohol for surface ablations. Additional use of woundhealing modulators, growth factors, or autologous serum may be adjunctive in EpiLASIK (10,11).

REFERENCES

1.Rouweyha RM, Chuang AZ, Mitra S, Phillips CB, Yee RW. Laser epithelial keratomileusis for myopia with the autonomous laser. J Refract Surg; 2002; 18(3):217–224.

2.Claringbold VT. Laser-assisted subepithelial keratectomy for the correction of myopia. J Cataract Refract Surg; 2002; 28:18–22.

3.Shahinian L. Laser-assisted subepithelial keratectomy for low to high myopia and astigmatism. J Cataract Refract Surg; 2002; 28:1334–1342.

4.Anderson NJ, Beran RF, Schneider TL. Epi-LASEK for the correction of myopia and myopic astigmatism. J Cataract Refract Surg; 2002; 28:1343–1347.

5.Pallikaris JG, Naoumidi II, Kalyvianaki MI, Katsanevaki VJ. Epi-LASIK: Comparative histological evaluation of mechanical and alcohol-assisted epithelial separation. J Cataract Refract Surg; 2003; 29:1496–1501.

6.Chen CC, Chang JH, Lee JB, Javier J, Azar DT. Human corneal epithelial cell viability and morphology after dilute alcohol exposure. Invest Ophthalmol Vis Sci; 2002; 43(8):2593–2602.

7.Stramer BM, Zieske JD, Jung JC, Austin JS, Fini ME. Molecular mechanisms controlling the fibrotic repair phenotype in cornea: implications for surgical outcomes. Invest Ophthalmol Vis Sci; 2003; 44(10):4237–4246.

8.Azar DT, Ang RT, Lee JB, Kato T, Chen CC, Jain S, Gabison E, Abad JC. Laser subepithelial keratomileusis: electron microscopy and visual outcomes of photorefractive keratectomy. Curr Opin Ophthalmol; 2001; 12(4):323–328.

9.Espana EM, Grueterich M, Mateo A, Romano AC, Yee SB, Yee RW, Tseng SC. Cleavage of corneal basement membrane components by ethanol exposure in laser-assisted subepithelial keratectomy. J Cataract Refract Surg; 2003; 29(6):1192–1197.

10.Lin N, Yee RW. Autologous Serum in LASEK.Philadelphia, PA: ASCRS, June 2002.

11.Yee SB, Lin N, Yee RW. Use of Autologous Serum to Reduce Haze after LASEK. Chapter 30.