Figure 1. Haze after Lasek

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1 EPILASIK is a new and much discussed form of Laser Vision Correction Surgery. Laser Vision Correction surgery in recent years has seen a trend back toward surface ablation and the newest iteration of this is epilasik. Surface ablation is regaining popularity for its safety profile. Lamellar surgery has potential problems related to flap creation such as flap abnormalities, dry eye, epithelial problems and ectasia. One of the most worrying longer term complications with lamellar surgery is ectasia and even corneas with no obvious predisposing risk factors have been (rarely) observed to develop ectasia[1, 2]. The goal of modern surface ablation techniques is to avoid the potential complications of Lamellar surgery whilst minimizing the traditional disadvantages associated with PRK such as pain, slow healing and scar formation. Many of the potential complications of lamellar surgery may be minimized with laser flap cutting techniques (Femtosecond lasers) which allow greater predictability of flap shape, integrity and thickness with are les dependant upon the anatomy of an individual cornea.[3] By creating planar flaps (in contrast to the meniscus flaps created with bladed keratomes) the flap has less tissue volume and the impact on corneal integrity, stability and biomechanics is minimized. There remain however cases for which even with predictable and defined flap parameters the creation of a flap in itself is contraindicated. Corneas with form fruste kerataconus, ill defined asymmetry, thin pachymetric readings (<500um), Anterior Basement Dystrophy and dry eye may be more safely treated with surface ablation. Surface ablation as PRK was largely replaced by LASIK due to the rapid healing and visual recovery that followed lamellar surgery. PRK also had the attendant problems of pain, delayed healing and possible haze formation limiting the final visual potential. (Figure 1)More recent surface ablation techniques have in common the goal of preserving the epithelial cells as a flap that is replaced at the end of the excimer ablation. Preservation of the epithelial layer may facilitate faster healing and visual recovery, minimize discomfort and reduce the risk of haze formation. The presence of the epithelial layer early in the post operative period may enhance healing through reduced levels of TGF Beta1 in the tear film [4], reduced keratocyte apoptosis, reduced myelofibroblast transformation and less chondroitin sulphate synthesis, all factors associated with haze formation.[5, 6]

2 Figure 1. Haze after Lasek Several methods are in use for removal of the epithelium in surface ablations; For PRK the epithelium is removed and discarded; mechanical removal either freehand or using devices such as the Amoils Brush is the most common approach though laser scraping can also be utilized. LASEK seeks to preserve the epithelium as a sheet which is replaced at the end of surgery. A dilute alcohol solution (20% alcohol for 20 seconds) is applied to facilitate separation of the epithelium from bowmans membrane at the level of the hemidesmasomes; [7](Figure 2) The epithelium is pushed to one side prior to the ablation then repositioned and protected with a bandage contact lens. The epithelium is considered non viable beyond the immediate post operative period due to alcohol toxicity.[8]

3 Figure 2. Plane of cleavage MMC is a powerful adjunct to surface ablations reducing the incidence of significant haze formation[9-11] Some surgeons use MMC routinely for all surface ablation whilst others never use it due to concerns re potential unknown long term toxicity. A common usage pattern is to reserve MMC for at risk treatments; 1. ablations of greater than 90um depth 2. retreatments for corneal haze 3. retreatments over prior flap complications such as buttonhole. 4. surface ablation on a lasik flap EPI-LASIK was developed as a procedure to reliably create a viable epithelial flap that would remain on the cornea after excimer ablation. Pallikaris et al recently described the technique in which a microkeratome is used to create the epithelial flap, preserving the integrity of the basement membrane and avoiding the use of alcohol and its consequent epithelial toxicity.[12, 13] Epilasik aims to preserve the basement membrane of the corneal epithelium (in contrast with lasek where the basement membrane is divided at the level of the lamina lucida). An intact basement membrane may provide a barrier function preventing the penetration of inflammatory cytokines into the corneal stroma thus

4 modulating the wound healing response. The intact basement membrane also increases the chance of survival of the basal epithelial cells. The place of Epilasik is refractive surgery will be determined by three parameters; 1. The ability of Epilasik keratomes to reliably create reproducible and viable epithelial flaps. 2. Evidence that preservation of the epithelial flap improves outcomes. 3. Evidence that the epithelial flap created with Epilasik isbetter than that created with LASEK. There can be no doubt that some cases of laser vision correction are more safely performed without the presence of a lamellar flap and it is to these cases that we now look to determine the relative benefits of Epilasik as compared with LASEK or PRK. The Epilasik procedure; The eye is draped and prepped as for Lasik. Local aneasthetic drops are instilled and a lid speculum positioned. The epilasik suction ring is positioned on the eye and vacuum applied. Vaccuum is similar to that used for lasik and visual blackout may occur along with pupil dilation. Chilled BSS is applied to the epithelium and the epithelial separator advanced (automatically) across the cornea to create the flap. Vaccuum is released and the epilasik unit removed from the eye. The epithelial flap is moved to one side taking care not to tear or stretch it. An epithelial flap is very soft and distensable. Experienced LASIK surgeons will need to revisit flap handling techniques to avoid stretching and tearing the apilasik flaps. After the excimer ablation, the stroma is irrigated with chilled BSS some advocate use of frozen pledglets. The epithelial flap is repositioned onto a relatively dry stromal bed and a contact lens placed on the eye. The contact lens placement technique is important to flap integrity. A favoured technique is to apply the inverted contact lens convex surface down onto the apex of the cornea and unfold the lens onto the cornea using forceps and a sponge. The bandage contact lens is left is situ for 3 to 5 days. Often at the time of lens removal the epithelium will be disturbed causing discomfort and a transient drop in vision. A comparison of four currently available EPILASIK keratomes.. All epilasik systems have in common ability to separate the epithelium from the underlying corneal stroma. Ease of use, predictability and reliability of flap creation, flap quality, patient comfort and universality of application are differentiating features. Norwood EyeCare Centurion

5 Dr Pallikaris developed the first epikeratomes after observing that microkeratomes with defective blades would separate the epithelium from the cornea without cutting stroma. The EpiEdge separator (now known as the Centurion) uses a blunt plastic separator blade to create the epithelial flap. The Centurion is different from the other epilasik units in using a blunt plastic block as the separator and having no corneal applanation plate. The earliest cases with the Centurion demonstrated that an epithelial flap could be created though there were several cases of incursions into superficial stroma. Redesigning the angle of engagement between separator and epithelium has resolved this issue. The Centurion separator safely pushes the epithelium in front of the separator without the epithelium passing through a slot or beneath an applanation plate. The epithelial flap thus created is potentially the least traumatized and stretched. We were able to consistently create a plane of cleavage between epithelium and stroma with no stromal incursions though commonly the Centurion epilasik separator left residual (unseparated) epithelial at the nasal region of the flap thus requiring mechanical debridement of epithelium to ensure an adequate zone for ablation. This seems to be a problem with lack of corneal applanation though further redesigning of the plastic separator configuration may solve this problem. This common and unpredictable residual epithelium limited the usefulnes of this unit. Moria EpiK(Figure 3) Figure 3. Moria

6 A modified microkeratome forms the basis for the Moria epilasik unit. A steel blade is used to separate the epithelial flap and there is a large corneal applanation plate. The epithelial flap passes through a space between blade and head on both forward and reverse passes. The Moria unit safely separated epithelial flaps though these were often torn and ragged requiring complete removal. The fragile epithelial flap appeared to be traumatized by being dragged through the head and dragged by the applanation plate. The unit was the most cumbersome to use and slowest in transition across the eye with the longest duration of suction. Gebauer EpiLift(Figure 4) Figure 4. Gebauer A sharp metal blade is used with a small applanation plate to create a precise angle of engagement between epithelium and separator. Assembly of the unit is quite fiddly. Reliable separation of epithelium from stroma was achieved with no stromal incursions though some flaps were discarded due to being torn and ragged. Amadeus (AMO)(Figure 5)

7 Figure 5. Amadeus An Epilasik head has been designed for use with the existing Amadeus2 keratome. This is a simple and elegant epilasik keratome and was the easiest to use and most intuitive of the 4 units tested. One free cap was created with the Amadeus Epi unit due to an inappropriate choice of hinge size. The epithelial flaps were minimally stretched and of high quality. Can a viable epithelial flap be created reliably and reproducibly with epilasik keratomes? Yes, each of the units was able to create a safe epithelial flap though there was some variability in the predictability and flap quality between units tested. No harm was caused even in cases where the flap was too ragged to retain; stretched flaps could be draped across the stroma (but were NOT observed to retract back to the wound edge with time). (Figure 6)Flap handling is different to LASIK flaps and we chose to smooth out the epithelium rather than aligning the flap edge with the margin of the stromal bed. Aligning the flap edge often results in large wrinkles in the central epithelial flap that took several days to disappear.

8 Figure 6. Stretched epithelium Variable healing and adhesion of the epithelial flap means that often at the time of contact lens removal at day 5 post op some of the central epithelium will slough. This heals quickly but does cause discomfort and reduced visual acuity. Contact lenses with base curves of 8.6 and 8.9 were used and there was no apparent difference between these in terms of epithelial stability. Is the apilasik flap viable and is it better than the flap created with alcohol assisted LASEK? Physically the epithelial flap is viable as demonstrated by its integrity at the end of surgery. The plane of separation with epilasik is at the level of the lamina densa so that the entire basement should be intact with the epithelium. With alcohol assisted separation the plane of cleavage is at the lamina lucida and hemidesmasomal attachments so that the basement membrane is cleaved and only partially attached to the epithelial flap. This results in death of basal epithelial cells and compromises survival of the epithelial flap. [14] Katsenevaki presented data at the ASCRS 2004 showing up to 99% viability of epithelial cells 24 hours after epilasik epithelial flap creation (with the Centurion epilasik unit) Defects in the basement membrane were however commonly observed. Differences in

9 epithelial viability will almost certainly become evident for flaps created with different epilasik systems as different systems will separate epithelium at slightly different levels dependant upon the nature of the epithelial separator sharp blade vs blunt plastic blockand configuration of the cutting head design. LASEK has the benefit of not requiring suction and raised intraocular pressure to create the flap. It is also inexpensive requiring no capital outlay and minimal per procedure costs. The epithelial flap however is not as predictably created with LASEK (compared with Epilasik). Similarly flap integrity is more variable with LASEK and flap survival shorter. Epilasik allows creation of an epithelial flap that will survive and reattach to the underlying corneal stroma. Epilasik in practice today Surface ablations are an important part of safe laser vision correction practice. Theoretically preservation of an epithelial flap will enhance healing and reduce the incidence of haze formation after surface ablation. Clinical studies are being reported to confirm this theoretical benefit[15, 16] though there is conflicting data suggesting no benefit of LASEK over PRK.[17] A well conducted prospective randomized trial in the military comparing PRK with LASEK showed no benefit with epithelial preservation.[18] Femtosecond laser cutting systems have enhanced the safety and predictability of lamellar flap creation. Many of the reasons for moving to surface ablation are removed when a thin flap of predictable thickness can be created without the potential problems that were intrinsic to mechanical microkeratomes. Lamellar surgery certainly has the benefit of fast healing with rapid visual recovery that Epilasik does not reproduce. More predictable flap parameters with a narrow variance from intended thickness will reduce ectasia concerns and the trend to surface ablation may slow. Surface ablation is safer for select patients. If prospective randomized contralateral eye studies can demonstrate a benefit with preservation of the epithelial flap Epilasik will become the standard of care for surface ablation.

10 1. Lifshitz T, Levy J, Klemperer I, Levinger S: Late bilateral keratectasia after LASIK in a low myopic patient. J Refract Surg 2005; 21(5): Binder PS: Ectasia after laser in situ keratomileusis. J Cataract Refract Surg 2003; 29(12): Binder PS: Flap dimensions created with the IntraLase FS laser. J Cataract Refract Surg 2004; 30(1): Lee JB, Choe CM, Kim HS, Seo KY, Seong GJ, Kim EK: Comparison of TGF-beta1 in tears following laser subepithelial keratomileusis and photorefractive keratectomy. J Refract Surg 2002; 18(2): Esquenazi S, He J, Bazan NG, Bazan HE: Comparison of corneal wound-healing response in photorefractive keratectomy and laser-assisted subepithelial keratectomy. J Cataract Refract Surg 2005; 31(8): Laube T, Wissing S, Theiss C, Brockmann C, Steuhl KP, Meller D: Decreased keratocyte death after laser-assisted subepithelial keratectomy and photorefractive keratectomy in rabbits. J Cataract Refract Surg 2004; 30(9): Browning AC, Shah S, Dua HS, Maharajan SV, Gray T, Bragheeth MA: Alcohol debridement of the corneal epithelium in PRK and LASEK: an electron microscopic study. Invest Ophthalmol Vis Sci 2003; 44(2): Dai JH, Chen CD, Chu RY, et al.: [Clinical investigation of epipolis laser in situ keratomileusis on high myopia]. Zhonghua Yan Ke Za Zhi 2005; 41(3): Camellin M: Laser epithelial keratomileusis with mitomycin C: indications and limits. J Refract Surg 2004; 20(5 Suppl): S Carones F, Vigo L, Scandola E, Vacchini L: Evaluation of the prophylactic use of mitomycin-c to inhibit haze formation after photorefractive keratectomy. J Cataract Refract Surg 2002; 28(12): Cheng Z, Li J, Cai K, Li R, Li H, Qin X: [Effects of mitomycin C on haze after photorefractive keratectomy for myopia in rabbits]. Zhonghua Yan Ke Za Zhi 1998; 34(6): Pallikaris IG, Kalyvianaki MI, Katsanevaki VJ, Ginis HS: Epi-LASIK: preliminary clinical results of an alternative surface ablation procedure. J Cataract Refract Surg 2005; 31(5): Pallikaris IG, Katsanevaki VJ, Kalyvianaki MI, Naoumidi, II: Advances in subepithelial excimer refractive surgery techniques: Epi-LASIK. Curr Opin Ophthalmol 2003; 14(4): Pallikaris IG, Naoumidi, II, Kalyvianaki MI, Katsanevaki VJ: Epi-LASIK: comparative histological evaluation of mechanical and alcohol-assisted epithelial separation. J Cataract Refract Surg 2003; 29(8): Autrata R, Rehurek J: Laser-assisted subepithelial keratectomy and photorefractive keratectomy for the correction of hyperopia. Results of a 2-year follow-up. J Cataract Refract Surg 2003; 29(11): Autrata R, Rehurek J: Laser-assisted subepithelial keratectomy for myopia: two-year follow-up. J Cataract Refract Surg 2003; 29(4):

11 17. Litwak S, Zadok D, Garcia-de Quevedo V, Robledo N, Chayet AS: Laser-assisted subepithelial keratectomy versus photorefractive keratectomy for the correction of myopia. A prospective comparative study. J Cataract Refract Surg 2002; 28(8): Pirouzian A, Thornton JA, Ngo S: A randomized prospective clinical trial comparing laser subepithelial keratomileusis and photorefractive keratectomy. Arch Ophthalmol 2004; 122(1): 11-6.