Butterfly LASEK

Butterfly LASEK

Paolo Vinciguerra and Fabrizio I. Camesasca

Department of Ophthalmology, Istituto Clinico Humanitas, Milano, Italy

Introduction

LASEK was first presented in 1999.1 Its use is slowly gaining ground because of its favorablecomparisonwiththeothertwoexcimerrefractivetechniquesavailable:LASIK and PRK. Since the medico-legal problems regarding refractive surgery are increasing throughout the Western world, ophthalmologists are paying particular attention to any surgical techniques that may reduce complications and provide reliable results.

Low epithelial viability is a postoperative complication of standard LASEK that hampers rapid postoperative recovery. In this reduced viability, the epithelial flap has a grayish appearance, with reduced transparency. Epithelial cell adhesion to the corneal stroma is reduced, and corneal debris can be observed under the protective contact lens in the immediate postoperative period. A non-viable, gray flap can be lost in the immediate postoperative period, thereby forfeiting the advantages offered by LASEK. Stromal protection is decreased, with consequent ocular discomfort. Visual acuity is reduced, and only when the epithelial flap is reattached to the limbus does this situation improve rapidly.

We present a modification of the LASEK technique which preserves the connection between the corneal flap and limbus. This connection is essential for re-establishing corneal epithelial adhesion and stratification.

Surgical technique

Preoperative anesthesia is administered by two applications of oxybuprocaine chlorhydrate eyedrops. The patient is prepped and draped, and a lid speculum is applied. Lidocaine 4% eyedrops are instilled. Using a specifically designed spatula (Vinciguerra’s spatula, ASICO, CA), a thin abrasion of 0.75 mm is made on the paracentral corneal epithelium, from 8 to 11 o’clock, in order to spare the optical zone. After positioning the LASEK fluid-holding ring, a 20% solution of alcohol and balanced salt solution (BSS) is applied to the cornea for a time ranging from five to 20

Address for correspondence: P. Vinciguerra, MD, Istituto Clinico Humanitas, via Ripamonti 205, I20141 Milano, Italy. e-mail: vincieye@tin.it

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Proceedings of the 51st Annual Symposium of the New Orleans Academy of Ophthalmology, New Orleans, LA, USA, February 22-24, 2002

edited by Jill B. Koury

© 2003 Kugler Publications, The Hague, The Netherlands

Fig. 1. Using a specially designed spatula (Vinciguerra’s spatula, ASICO, CA), a thin abrasion of 0.75 mm is made on the paracentral corneal epithelium, from 8 to 11 o’clock, sparing the optical zone. Using the same spatula and after applying a 20% solution of alcohol and BSS, the epithelium is gently dissected from Bowman’s membrane up to the limbus.

seconds, according the firmness of the epithelial adhesion noted during the initial abrasion.

Using the above-mentioned spatula, the epithelium, with its basal membrane, is gently dissected from Bowman’s membrane up to the limbus (Fig. 1). After application of the alcohol solution, it is mandatory to keep the epithelium well hydrated in order to preserve the loosening effect obtained.

If this hydration is not properly maintained, after the time needed to dissect the first flap, the second flap will be dehydrated, thus hampering easy dissection. During creation of the flaps, care must be taken not to perforate them inadvertently.

Before ablation, the stromal surface is carefully dried. The flap must be maintained moist. In order to keep the flap safely folded peripherally and to prevent its ablation, a specially designed retractor/protector is placed in position (Vinciguerra’s retractor FCPS, ASICO, CA) until the excimer ablation is complete (Fig. 2).

After refractive laser ablation, a smoothing phase is performed. This achieves a regular stromal bed, as similar as possible to the physiological Bowman’s membrane. Smoothing is performed by a hyaluronic acid masking fluid (Laservis, Chemedica, Munich) continuously being distributed over the surface with a special spatula (Buratto’s spatula, ASICO, CA). The smoothing diameter should be at least 9.5 mm, and should involve the entire corneal surface, thus preventing a hyperopic shift. During the procedure, it is mandatory continuously to add and evenly distribute the masking fluid, in order to avoid the formation of dry areas. Ablation on a dry area would not create the desired smoothing, but just localized ablation. In order to avoid overheating of the tissue, the ablation is set at 30 m, with a frequency of 10 Hz. Because of the masking fluid, the actual ablation is 8 m.

Once the smoothing phase is complete, the retractor/protector is removed and the epithelial flaps are gently repositioned over Bowman’s membrane, using the

Fig. 2. In order to keep the flap safely folded peripherally and to prevent its ablation, a specially designed retractor/protector (Vinciguerra’s FCPS retractor, ASICO, CA) is placed in position until excimer ablation is complete.

Vinciguerra/Carones spatula, with their margins overlapping. Finally, a protective contact lens is placed in position.

Clinical results

We treated both eyes of 35 patients by means of butterfly LASEK. Preoperative mean SE refraction was 5.3 ± 3.7 D. In all patients, the protective contact lens was removed no later than four days after surgery. No flaps were lost or displaced. At 12 months’ follow-up, the mean SE refraction was -0.1 ± 0.4 D, and no lines of BCVA had been lost. Refractions at one, three, six, nine, and 12 months are shown in Figure 3. Ninety percent of patients mentioned the greater comfort obtained with butterfly LASEK than with conventional LASEK. At 12 months, no patients showed more than a trace of corneal haze, and in 96.2% of patients the cornea was completely clear.

Discussion

The most evident advantage of standard LASEK compared to LASIK is elimination of problems regarding ectasia, interface impurities, irregularity, and epithelialization, as well as flap striae, folds, and interlamellar keratitis.2-6 In addition, LASIK requires a 160- m flap plus a 250- m stromal bed, making a total of 410 m of corneal thickness that must be preserved. This limitation often does not allow the creation of optical zones wide enough to fit the patient’s pupil diameter. For the same reason, undercorrection must, at times, be planned in highly myopic patients. Moreover, present-day studies highlight the biomechanical changes induced by flap creation in LASIK, with consequently induced optical aberrations, such as spherical aberration

Fig. 3. Butterfly LASEK. Postoperative refraction at one, three, six, nine, and 12 months.

and trefoil.7,8 Conversely, LASEK allows ablation of up to 200 m, and it does not lead to other typical LASIK complications, such as folds, interface or flap defects, or ectasia, which do not improve with time. Since it does not require a flap, LASEK leaves more corneal tissue available for retreatment.

The comparison of results obtained with LASIK and PRK could be biased by the fact that present-day LASIK is being compared with PRK performed ten years ago, with older generation lasers. Better quality lasers mean wider optical zones, smoother surfaces, and better transition zones. As discussed in previous studies, wide optical zones lead to the reduction of night halos, better surface quality to more precise refractive results, as well as to less haze, and better transition zones lead to a reduction in centroperipheral eccentricity with less induced regression as a consequence.9,10

When compared to PRK, LASEK reduces the risk of haze, regression, and postoperative pain. Corneal haze is a complication typical of PRK, and is less commonly observed with LASIK. With LASEK, haze appears to be rare and is limited in severity. As is the case with PRK, when present, it will decrease progressively in two to three years. Present-day retreatment for haze, coupling the smoothing technique and mitomycin, leads to excellent results. Another typical PRK complication, delay in re-epithelializa- tion, is prevented when adopting LASEK, and also other rarer but unpleasant problems, such as corneal dehydration following loss of contact lens in the immediate postoperative period, can be reduced or completely avoided. Therefore, LASEK appears to provide a limited risk of complications and can be applied to a greater number of patients than PRK.

Butterfly LASEK provides a more rapid return to epithelial transparency, indicating improved flap vitality and consequent faster visual recovery, than the standard LASEK technique. The less postoperative flap loss in butterfly LASEK is related to the better connection of the flap to the limbus.

Initially, when performing butterfly LASEK, the surgeon may encounter problems relatingtothelearningcurve.Forexample,postoperativepainisrelatedtothesurgeon’s skill in limiting corneal trauma and in creating an epithelial flap in a short time. Less manipulation and pressure on the cornea indicates reduced postoperative pain.

Conclusions

The advantages offered by butterfly LASEK with respect to presently available ablation techniques are clear. Butterfly LASEK permits better flap viability, greater patient comfort, faster visual recovery, as well as refractive stability over time.

In the future, customized ablation will require focal ablations, limited in microns in order to eliminate optical aberrations. The biomechanical effects induced by LASIK flap creation, as well as the problems related to flap irregularity, an effect due to flap adaptation to the stromal bed, and the limits in ablation depth, may all diminish the effect of these customized, focal ablations. Due to its fewer biomechanical and flap masking effects on ablation, LASEK appears to be the more appropriate technique for future customized ablation.

References

1.Camellin M, Vinciguerra P, Nizzola GM: LASEK: laser epithelial keratomileusis: a new technique for improving healing and decreasing postoperative pain. (Communication, 1999 Meeting of the American Society of Cataract and Refractive Surgeons, best paper in the section)

2.Vinciguerra P, Camesasca FI: Butterfly laser epithelial keratomileusis for myopia. J Refract Surg (in press)

3.Azar DT, Ang RT, Lee JB et al: Laser subepithelial keratomileusis: electron microscopy and visual outcomes of flap photorefractive keratectomy. Curr Opin Ophthalmol 12:323-328, 2001

4.Kornilovsky IM: Clinical results after subepithelial photorefractive keratectomy (LASEK). J Refract Surg Suppl 17(2):S222-223, 2001

5.Scerrati E: Laser in situ keratomileusis vs laser epithelial keratomileusis (LASIK vs LASEK). J Refract Surg Suppl 17(2):219-221, 2001

6.Lee JB, Seong GJ, Lee JH et al: Comparison of laser epithelial keratomileusis and photorefractive keratectomy for low to moderate myopia. J Cataract Refract Surg 27:565-570, 2001

7.Roberts C: The cornea is not a piece of plastic. J Refract Surg 16:407-413, 2000

8.Roberts C: Future challenges to aberration-free ablative procedures. J Refract Surg 16:S623629, 2000

9.Vinciguerra P, Azzolini M, Airaghi P, Radice P, De Molfetta V: Effect of decreasing surface and interface irregularities after photorefractive keratectomy and laser in situ keratomileusis on optical and functional outcomes. J Refract Surg 14(2):S199-203, 1998

10.Vinciguerra P, Azzolini M, Radice P, Sborgia M, De Molfetta V: A method for examining surface and interface irregularities after photorefractive keratectomy and laser in situ keratomileusis: predictor of optical and functional outcomes. J Refract Surg 14(2):S204-206, 1998

Questions and Answers on “Scleral expansion bands for the correction of presbyopia”

(Barry Soloway, MD)

Moderator: Our first question is, what postop drops do you use for LASEK, and the second part of that is, what is the highest correction you are doing for LASEK, and are you using mitomycin?

Paolo Vinciguerra, MD: The first question is that the postoperative regimen is just antibiotic eyedrops twice a day, and nothing else until we remove the bandage lens. Of course, Ionnis Pallikaris made a very important point. Why we need to leave these lenses so long, because even if the epithelium appears to be very healthy and good from the first postoperative days, the adherence is not complete. So, if you remove before, you can have a late loss of your flap. I use steroids after removal of the lens, just for reducing the postoperative discomfort, for one week. I use fluorometholone twice a day for just one week. We don’t see haze, we don’t see regression. I think we do this, not for the sake of the epithelial flap, but for the smoothing, because we have the same good outcome with the old PRK era when we apply smoothing. That is the real point. It is not only the exterior flap. I never use mitomycin. I only use mitomycin in PTK cases, never for refractive purposes. Concerning the maximal value we operate, we go up to 14 diopters. I know it is strange to hear this value, but think about it, first of all we have more freedom, we don’t have any single ectasia in years of treatment, and the key point is the algorithm. You can treat this if you instantaneously avoid the red ring that is the spherical aberration. Otherwise, the real optical zone is very small.

Moderator: I have a corollary to that question regarding LASEK. What preoperative drops do you use, and is there any schedule for the anesthetic drops you use to soften the epithelium?

Daniel S. Durrie, MD: Just to follow on with what Paolo said, and I am going to report some data on this after the break, but you are hearing a lot about people using mitomycin and strong steroids on high myopes, and the data don’t support that. I am really worried about a lot of people starting this technique and putting a lot of toxic things on the cornea until we have data that they need that. So, in our series, in my first 154 eyes, we didn’t use steroids at all, other than in the first couple of days, and haze was really not a problem. We are adapting some of the US lasers so we can do smoothing, but even without smoothing, with the fine spot lasers that are much smoother now, we really didn’t see haze that way either. So,

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edited by Jill B. Koury

© 2003 Kugler Publications, The Hague, The Netherlands

don’t over-medicate these patients, because you will have steroid-induced glaucoma. You are also going to have some of the problems we saw before with infections. I think the other key thing is the contact lens. What contact lens to use. And we did a randomized prospective study comparing different available extendedwear contact lenses and found that non-ionic medium water contact lenses were significantly better than the ionic lenses. I didn’t even know what those terms meant before I did this study. The ionic lenses have a positive charge and will attract a lot of proteins. This procedure has slightly more proteins than other ones. Lenses like an Acuvue, which a lot of people would be thinking about using, are ionic lenses. So, the one we have been using is a Bausch and Lomb 66, which is one of the extended-wear lenses, and it seemed to perform the best. So, picking the right contact lens, the company Ciba is working on a new ProTek version for this procedure. In Europe they are probably looking at that. So the contact lens is important. With regard to anesthetics to try to soften the epithelium, this gets into a whole new field. We don’t know what the best is to use. I am doing randomized prospective studies with one eye with one chemical, one eye with the other chemical, and I think that this is the only way we can figure these out. These are in progress.

Dr Vinciguerra: I treat the epithelium in LASEK like the epithelium in LASIK. I just put in anesthetic drops a few seconds before. I don’t want to weaken the epithelium before surgery, and just one drop of procaine on the cornea and lidocaine on the conjunctiva, but just a few seconds before, nothing else.

Moderator: Any other preoperative drops or medications?

Dr Vinciguerra: No, nothing.

Moderator: The next question is, have you performed any enhancements using the LASEK technique following PRK or LASEK?

Dr Durrie: I am going to show a video on that with my lecture, but, yes, you can do it. Fortunately, they are not needed very often.

Dr Vinciguerra: It is very uncommon to have to retreat these patients. The lifting of the epithelium, how easy it is in relation to how smooth the surface was immediately after. If you had a bad PRK and you try to lift the epithelium, you destroy it, because it is in such strict conjunction that it is very difficult. The surface, if it is smooth like a Bowman, is easy to lift. But, the other important point is, even if you are treating high myopes, you always have tissue available for retreatment. This is not always the case with LASIK, where you use all the available tissue for the optical zone.

Moderator: Let’s continue with the LASEK questions and then move on. Any increase in recurrent erosions with LASEK?

Dr Vinciguerra: I don’t have any cases on this.

Moderator: What changes in your LASIK or LASEK procedure do you make for a patient who is post-RK status?

Dr Durrie: We did a study several years ago, and this wasn’t with modern surface ablation techniques. It wasn’t with LASEK, it wasn’t with modern lasers, but we did an FDA prospective study on PRK over RK, and 25% of the patients had significant haze with loss of best corrected vision. So, I would move very cautiously in this area. We are doing a study on modern LASEK with modern lasers over RK, but I am not really advising it yet. Because we didn’t see some of the haze in these patients until quite late, and it was significant. So, I think that standard LASIK can be done over RK, and that is still my treatment of choice. I’d like to hear if anybody else has tried it and their comments.

Dr Vinciguerra: I recommend going back to yesterday when Stephen Slade talked to us. Every time you have a cornea that has already been treated, regardless of whether by graft or RK, that is not well suited for surface ablation because we have terrible haze. It can be treated for PTK, but not for refractive purposes. We have terrible haze. I don’t recommend doing this.

Moderator: Does anyone have data on LASIK retreatments?

Dr Durrie: That is almost the same question. I have done them, but I don’t have data. It’s such a small series. You can do it.

Moderator: Dr Pallikaris, everybody wants to know what instrument you are using to make that epithelial flap, is it a laser or is that...secret?

Dr Vinciguerra: I think you will see this very soon, after a few months perhaps. I can’t talk about it quite yet.

Moderator: Dr Soloway, here you go. Number one, are the scleral bands visible?

Barry Soloway, MD: They are visible, certainly if somebody is up close, and certainly if the eye is looking in an oblique quadrant. When you are just looking at a person, a lot would depend on the status of their lids, how much ptosis they have, whatever. Generally speaking, I would say that they are not generally visible. It is certainly not something that has come back to us as a problem, with patients complaining that, cosmetically, people are seeing them.

Moderator: Okay.

Dr Soloway: Do I believe Schachar’s theory or the Catinary theory? I guess that is Coleman’s theory. I have come to the conclusion in my mind that I am not sure what the theory of presbyopia is. I think it is a lot of things. I think we are going to find presbyopia, or I guess we are already finding presbyopia, to be a lot like DLK in that it is multifaceted in what is going on in people’s vision. We have had people from Ciba coming into the office to see patients, and basically their feeling was that we are teaching patients to read in a different way. So, I am not sure which theory is correct.

Ioannis G. Pallikaris, MD: I have a presentation in the next session about vision

dynamics and I think I can give you some idea of how the lenses react during

accommodation based on...

Raymond A. Applegate, OD, PhD: I’d also like to make a comment. When you talk about accommodation, you have to have a change of power in the eye, and one of the things that would convince, at least the scientists, and I think the clinicians, is to measure whether the power of the eye is changing, instead of measuring acuity. So I would really encourage – and Barry, you are in a great place to do this – the use of just one of these aberrometers, like I am sure Ionnis is going to talk about, that can measure whether the power of the eye is actually changing or not.

Dr Soloway: In the next session, I have some data that I will be showing in terms of objective...unfortunately, we haven’t been able to get one of the units.

Dr Vincinguerra: Just a brief comment. Think about it. Even the young people who underwent vitreous surgery, so we removed the entire vitreous, still accommodate. So when you are thinking about these theories, think that, even without vitreous, the accommodation is still working.

Moderator: This sounds like the first session is a tease, there’s more to come. Dr Soloway, you’re not done yet. About suturing of the bands, was there any suturing involved?

Dr Soloway: No suturing on the bands. There hasn’t been since the bands went to four segments. There hasn’t been any suturing. The current bands are held in place by the small ridges on the underside as they come out of the wound. The only suturing done is to bring the conjunctiva up to close the band. What we have seen is, if the conjunctiva isn’t fully covering the band, you get a scleral melt and the band will just come out.

Moderator: The next one for you is how do you account for the bilateral effect described in monocular placement of the subepithelial bands?

Dr Soloway: In my practice, we have certainly seen an improvement in the other eye in those six patients. It is nowhere near, it’s typically about a third, and it is thought that that may be how the patient is testing, and just learning the test better or learning to read better. We typically subtract that and show that at least twothirds of the improvement is due to the bands themselves.

Moderator: Finally, what objective data do you have on your patients?

Dr Soloway: I have saved the objective data for the next session. I didn’t mention change in diopters. I am going to be talking about that in the next session, and the change in measurements from preop to postop was what I was showing on that slide I showed with decimal acuity.

Moderator: Okay, last two questions. Dr Durrie alluded to subepithelial haze. Is it visually significant or just something that the doctor sees?

Dr Durrie: What I like about going back to surface ablation is that we have a lot of experience in this. We just have to remember back a few years. John Marshall did some excellent work to show that the haze the patient is looking through is totally different from what we see. So, what we are seeing is just basically a reflection of the light at the slit lamp, and describing it from our side. But the light, the little reticular dusting of less than trace haze that we see in almost all surface ablations, doesn’t affect the patient’s visual quality at all. The thing we saw when PRK was released worldwide was that there were a lot of people who saw a little something on the cornea that bothered them, and then they put a lot of steroids on it or they tried to scrape it off, or they tried to do other things, and they turned it into a scar. And I am worried that, if surface ablation comes back, especially with a lot of co-management going on, we are going to have people overreacting again to things they see at the slit lamp. So one thing is that John Marshall’s paper should probably be re-edited and republished again so that people can say, don’t treat something that is not bothering the patient. This is happening right now with the doctors in our office. As soon as they see something on the cornea that doesn’t look like standard LASIK, they feel they have to put the patient on steroids or do something, and then say, “How is the patient seeing?” “Oh, they were 20/10 and they were seeing fine, but I was worried that they needed something”. So I don’t want to overreact to what we see at the slit lamp.

Dr Pallikaris: I’d like to make a comment. We know that there are two different kinds of haze. The haze we are seeing and the haze the patient is seeing. And, for the first few months after treatment, the patient probably is seeing this haze because it is haze related to activation of the healing process and light that is coming through the cells which is activated on the cornea. So, we have a large scattering of the light coming through, and that is what the patient sees. When the haze later becomes more of a scar, it’s like when you put your fingers in front of your eye and you can see something through them very nicely, so this is the haze that the patient does not see.

Dr Vinciguerra: I have a simple recommendation, which we discovered with Scheimpflug images when you compare the preoperative and the postoperative pupil. If the postoperative one is a little wider, this means that the scattering is sensitive to the patient, as is needed in order to enlarge the pupil to get the same light entry. If you stay in the pupil, there isn’t any significance for the patient. So, it is an objective measurement that allows you to make an evaluation.

Moderator: Dr Vinciguerra, while you have the microphone, when you made your paracentral abrasion, were you just using your flap elevator, or was there a separate instrument?

Dr Vinciguerra: It is the same spot. To do the central debridement, I basically use the same instruments: the spatula, the retractor, and the one I use for smoothing, to remove the flap – three instruments.

Moderator: And finally, Dr Soloway, you alluded to perforation as a potential complication when making those flaps. Have you encountered this? What do you do about it? How bad is it?

Dr Soloway: This has been reported a number of times. I have actually had one patient in whom I ended up submarining a band. The band was left in. Generally speaking, it’s left in. It’s polymethylmethacrylate, as the British fighters in World War II, and we have found out that it’s certainly safer to leave it in the eye. We place the band over that area and have gotten good results. Actually, that patient of mine has a small filtering bleb right in that area, but it’s well covered with conjunctiva. He is seeing well, it is not bothersome to him.

Epi-LASIK: a new refractive technique

Histological evaluation and human study

Ioannis G. Pallikaris, Irene I. Naoumidi, Maria I. Kalyvianaki and Harilaos S. Ginis

University of Crete, School of Medicine, Vardinoyannion Eye Institute of Crete, Heraklion, Crete, Greece

Introduction

Photorefractive keratectomy (PRK) has proved to be a predictable and safe method for the treatment of low to moderate levels of refractive error.1,2 The main drawbacks of PRK are postoperative pain, late recovery, prolonged use of steroids, and the risk of postoperative haze in the treatment of high ametropia.3 Laser-assisted in situ keratomileusis (LASIK) effectively addressed these problems, by creating a corneal flap and performing laser ablation on the exposed stromal bed.4 However, there are several possible complications related to flap creation in LASIK. Among these, the most common are irregular flaps, epithelial ingrowth, and corneal ectasia.5,6

Moreover, the use of wavefront-sensing devices has shown an increase in high order aberrations induced by LASIK.7 These aberrations are attributed to modification of the biomechanical properties of the cornea after flap creation. Additionally, wavefront-guided treatments are more effective when performed in the PRK mode than with LASIK.8

A technique called LASEK was introduced by Camellin in 1999 (“LASEK may offer the advantages of both LASIK and PRK”, Ocular Surgery News, International Edition, March 1999). This technique is based on the creation of an epithelial flap after instillation of an alcohol solution on the cornea. This epithelial flap is repositioned on the cornea after ablation has been performed. Various concentrations of alcohol have been used for different lengths of time (20 seconds to two minutes) for the loosening of the epithelial layer.9-11 Lee et al. reported that LASEK-treated eyes had lower pain scores and corneal haze scores at one month postoperatively, compared to PRK-treated eyes.12 Scerrati suggested that LASEK might be superior to LASIK regarding the uniformity of corneal topography, best-corrected visual acuity, and contrast sensitivity data at six months postoperatively.13 Shah et al.

Address for correspondence: Maria I. Kalyvianaki, MD, Voutes PO 1352, Heraklion 711 10, Crete, Greece. e-mail: mariakalyvianaki@hotmail.com

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edited by Jill B. Koury

© 2003 Kugler Publications, The Hague, The Netherlands

considered managing the epithelium as a hinged flap with 20% alcohol a better choice than epithelium debridement with alcohol.14 Claringbold presented a retrospective study of LASEK-treated eyes with good refractive and visual results.15 Despite the encouraging results with LASEK, concern has arisen about the toxic effect of alcohol on the epithelium and on the underlying corneal stroma.15,16 There is no histological evidence in the literature to clarify whether the epithelial cells remain vital after the application of alcohol on human eyes, or regarding the extent of alcohol penetration into the stroma. Moreover, the procedure involves many manipulations of the epithelium in connection with its detachment and replacement on the ablated stroma. These manipulations require special surgeon training. The technique known as Epi-LASIK, which we are proposing, is based on separation of the corneal epithelium by mechanical means. This separation is performed using a modified microkeratome with a blunt blade, which has been manufactured at our institute. After detachment of the epithelial flap, ablation is performed. Then the epithelial flap is repositioned on the stroma and a contact lens is placed on the

eye.

The purpose of the present study is to histologically evaluate the effectiveness of this new technique in terms of separated epithelial cell viability, and to compare the histological appearance of these cells with that of epithelial samples separated using the LASEK technique.

Subjects and methods

Six eyes of six patients underwent Epi-LASIK for epithelial separation. Epithelial flaps were removed, and surgery was converted to PRK. Four other eyes of four patients underwent the LASEK procedure and separated epithelial discs were also removed. Two of the four LASEK eyes were treated using a 15% alcohol concentration for 20 seconds, while the remaining two were treated using a 30% concentration for the same amount of time.

All separated epithelial flaps underwent light and electron microscopy. Histological findings from the mechanically created epithelial flaps were compared to those from the epithelial flaps created after exposure of the cornea to alcohol.

Fixation of the specimens occurred immediately after separation, in a 2.5% glutaraldehyde in 0.1 M sodium cacodylate buffer solution, and they were then processed for light and electron microscopy. The specimens were embedded in epoxy resin, and stained with modified trichrome or uranile acetate and lead citrate.

Results

Mechanically separated epithelial layer

Light microscopic examination of the epithelial disc specimens carried out immediately after surgery revealed that the disc had a uniform thickness over its whole length, and the epithelial layer had retained the stratification and integrity typical of corneal epithelia (Fig. 1).

Electron microscopy of the epithelial discs demonstrated that the epithelial layer was separated under the level of the basement membrane.

Fig. 4b. Higher magnification of basal epithelial cells. Note the absence of lamina densa, while the thin fibrillar material of the lamina lucida is clearly defined (between the arrows). The tonofilaments of the epithelial cells (small arrowheads) appear to be firmly anchored to the basal attachment plates of hemidesmosomes (large arrowheads). Bar length corresponds to 0.1 µm.

The possible toxic effects of alcohol on the epithelial cells and on the underlying stroma led to the idea of detaching an epithelial flap prior to photoablation, by mechanical means and without the use of alcohol. For this purpose, a modified microkeratome with a blunt blade is used. It is important to evaluate histologically the epithelial separation made by this device, in order to demonstrate the condition of the epithelium after its separation and before its replacement on the stroma. Epithelial flaps obtained after the instillation of alcohol on the cornea were also examined histologically, in order to compare the results.

Mechanical epithelial separation under the level of the basement membrane during Epi-LASIK led to the healthy appearance of epithelial cells and normal structures of the epithelium. Separation of the epithelial layer with alcohol during LASEK took place at the level of basement membrane and caused extensive blebbing of the epithelial cells.

Therefore, the epithelial flap that is repositioned on the ablated stroma with LASEK has an abnormal appearance compared with the epithelial flap created with the modified microkeratome. Healthy, mechanically separated epithelial flaps may protect the ablated stroma. This could result in earlier visual recovery and less pain than experienced with PRK and LASEK.

Despite the encouraging histological results regarding mechanical epithelial separation, studies on the repositioning of epithelial flaps on the ablated stroma of human eyes, as well as on the follow-up of these patients, are needed to confirm the efficacy and safety of Epi-LASIK.

In conclusion, Epi-LASIK is a new promising technique which could well combine the advantages of LASEK and LASIK and eliminate their disadvantages.

References

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