Introduction
Definition and Terminology
Laser subepithelial keratomileusis (LASEK) combines certain elements of both laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK). In LASEK—instead of completely removing the epithelium, as with PRK—dilute alcohol is used to loosen the epithelial adhesion to the corneal stroma. The loosened epithelium is then moved aside from the treatment zone as a hinged sheet. Laser ablation of the subepithelial stroma is performed before the epithelial sheet is returned to its original position, as with the LASIK flap.
The first LASEK procedure was performed at the Massachusetts Eye and Ear Infirmary in 1996 by one of the authors (DTA). Camellin popularized the procedure and coined the term LASEK for laser epithelial keratomileusis. Alternative expressions include laser subepithelial keratomileusis, subepithelial photorefractive keratectomy, epithelial flap photorefractive keratectomy, laser-assisted subepithelial keratectomy, excimer laser subepithelial ablation, and epi-LASEK.
Theoretical Advantages of LASEK
The main rationale for combining elements of LASIK and PRK to LASEK is to avoid the flap-related LASIK complications and the slow visual recovery and haze risk of PRK.
LASEK may avoid several of the inherent complications, including free caps, incomplete flaps, flap wrinkles, epithelial ingrowth, flap melt, interface debris, corneal ectasia, and diffuse lamellar keratitis after LASIK and postoperative pain, subepithelial haze, and slow visual rehabilitation after PRK.
Definition and Terminology
Laser subepithelial keratomileusis (LASEK) combines certain elements of both laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK). In LASEK—instead of completely removing the epithelium, as with PRK—dilute alcohol is used to loosen the epithelial adhesion to the corneal stroma. The loosened epithelium is then moved aside from the treatment zone as a hinged sheet. Laser ablation of the subepithelial stroma is performed before the epithelial sheet is returned to its original position, as with the LASIK flap.
The first LASEK procedure was performed at the Massachusetts Eye and Ear Infirmary in 1996 by one of the authors (DTA). Camellin popularized the procedure and coined the term LASEK for laser epithelial keratomileusis. Alternative expressions include laser subepithelial keratomileusis, subepithelial photorefractive keratectomy, epithelial flap photorefractive keratectomy, laser-assisted subepithelial keratectomy, excimer laser subepithelial ablation, and epi-LASEK.
Theoretical Advantages of LASEK
The main rationale for combining elements of LASIK and PRK to LASEK is to avoid the flap-related LASIK complications and the slow visual recovery and haze risk of PRK.
LASEK may avoid several of the inherent complications, including free caps, incomplete flaps, flap wrinkles, epithelial ingrowth, flap melt, interface debris, corneal ectasia, and diffuse lamellar keratitis after LASIK and postoperative pain, subepithelial haze, and slow visual rehabilitation after PRK.
Alcohol-Assisted Epithelial Removal
Manual epithelial debridement produced scratches and nicking in the Bowman layer and left variable amounts of epithelium. Chemical agents such as 0.5% proparacaine, iodine, cocaine, alkali n -heptanol, and ethanol have been used to remove the corneal epithelium in experimental studies. Today, 18% to 20% ethanol diluted in sterile water or salt solutions is commonly used in LASEK. Early reports revealed that epithelial removal using 18% to 25% alcohol for 20 to 25 seconds was fast, easy, and safe compared to mechanical debridement. They also showed that this concentration can produce sharp wound edges and a clean, smooth Bowman layer and that the central epithelium can be translocated in part or completely. Trigo suggested diluting ethanol in artificial tears (polyvinylic alcohol, commercially available as Liquifilm and Allergan) to create a 20% solution that is supposed to cause less epithelial dehydration and trauma.
Effect of Alcohol on Epithelial Cell Survival In Vitro
Our in vitro studies also suggested a dose- and time-dependent effect of alcohol on epithelial cells. The 25% concentration of alcohol was the inflection point of epithelial survival. Significant increase in cellular death occurred after 35 seconds of alcohol exposure; 40 seconds of exposure further induced apoptosis after 8 hours incubation. These findings are consistent with clinical observations of variable epithelial attachment to the stromal bed on the first postoperative days after LASEK surgery and also with the use of greater than 50% ethanol in the treatment of progressive or recurrent epithelial ingrowth after LASIK.
The in vitro monolayered results may apply to in vivo multilayered epithelium. The critical alcohol concentration and its duration of exposure are thus frequently exceeded during surgery. Increased duration of alcohol application can be used intentionally to weaken the epithelial adhesions, which contributes to the variability in alcohol-induced toxicity that is observed in vivo.
Transmission Electron Microscopy of Corneal Epithelium Specimen
To study the effect of alcohol exposure and mechanical manipulation on corneal epithelium, we carried out electron microscopy studies on specimens obtained after conventional alcohol-assisted PRK. The images revealed that the epithelial cell layer is intact and the epithelial cells are still viable immediately after exposure to alcohol and surgical peeling ( Fig. 19.1 ). The presence of the basement membrane attached to the basal epithelial cell layer indicates that the point of separation was likely to be within the basement membrane or between the basement membrane and Bowman layer.
Use of Mitomycin C to Avoid Haze
Potential haze formation remains an issue after ablation of the superficial stroma. To date, only topical corticosteroids are widely utilized for modulation of wound healing after refractive surgery. They act by inhibiting activated keratocytes, probably by interfering with DNA synthesis, which decreases cellular activity and reduces collagen synthesis. The use of mitomycin C to modify the wound-healing process was proposed many years ago but is still controversial. The mitomycins are a group of antitumor antibiotics that covalently bind to DNA after reductive activation. Mitomycin C inhibits fibroblast function by a dose-dependent inhibition of fibroblast proliferation. We believe that the use of mitomycin C for treating patients with visually significant preexisting corneal scarring may be justified by the excellent data reported by Majmudar et al., Raviv et al. and others. Mirza et al. reported successful treatment of a patient with dense subepithelial haze after LASEK with mitomycin C. This is in concordance with our own experience using 0.02% mitomycin C applied to the center of the ablation bed for 1 min with a sponge (preferably donut shaped to avoid having the highest concentration in the center, where the cornea is thinnest). Our results suggest that the beneficial effect of mitomycin C may result from inhibition of keratocytes underlying the application zone. At present, there is a wide range of indications and dosages used. We do not use mitomycin C in routine cases. However, if the risk of haze formation seems higher than average owing to previous corneal laser surgery, we use mitomycin C 0.02% for 15 to 30 seconds, as recommended by Virasch et al.
Use of Mitomycin C to Avoid Haze
Potential haze formation remains an issue after ablation of the superficial stroma. To date, only topical corticosteroids are widely utilized for modulation of wound healing after refractive surgery. They act by inhibiting activated keratocytes, probably by interfering with DNA synthesis, which decreases cellular activity and reduces collagen synthesis. The use of mitomycin C to modify the wound-healing process was proposed many years ago but is still controversial. The mitomycins are a group of antitumor antibiotics that covalently bind to DNA after reductive activation. Mitomycin C inhibits fibroblast function by a dose-dependent inhibition of fibroblast proliferation. We believe that the use of mitomycin C for treating patients with visually significant preexisting corneal scarring may be justified by the excellent data reported by Majmudar et al., Raviv et al. and others. Mirza et al. reported successful treatment of a patient with dense subepithelial haze after LASEK with mitomycin C. This is in concordance with our own experience using 0.02% mitomycin C applied to the center of the ablation bed for 1 min with a sponge (preferably donut shaped to avoid having the highest concentration in the center, where the cornea is thinnest). Our results suggest that the beneficial effect of mitomycin C may result from inhibition of keratocytes underlying the application zone. At present, there is a wide range of indications and dosages used. We do not use mitomycin C in routine cases. However, if the risk of haze formation seems higher than average owing to previous corneal laser surgery, we use mitomycin C 0.02% for 15 to 30 seconds, as recommended by Virasch et al.
Surgical Techniques
The major surgical techniques are variations of PRK-like ablation under a epithelial sheet created in a different manner.
Azar Flap Technique
Our LASEK technique ( Fig. 19.2 ) evolved from PRK after alcohol-assisted epithelial removal. After application of topical 0.5% proparacaine (Ophthetic, Allergan, Inc.) and 4% tetracaine (formulated in a pharmacy), a lid speculum is applied. The cornea is then marked with overlapping 3-mm circles around the corneal periphery, simulating a floral pattern. An alcohol dispenser consisting of a customized 7- or 9-mm semi-sharp marker (ASICO) attached to a hollow metal handle serves as the reservoir for 18% alcohol. After 25 to 30 seconds, the ethanol is absorbed using an aspiration hole, followed by dry sponges (Weck-cel or Merocel, BVI). If necessary, the ethanol application may be repeated for an additional 10 to 15 seconds.
We then use ice-chilled, sterile salt solution to wash away any ethanol residues from the ocular surface and cool the cornea. Cooling the cornea to minimize postoperative pain and haze formation was originally described as early as 1994 for PRK.
Over time, the step of epithelial removal has been modified. Initially, one arm of a jeweler’s forceps was inserted under the epithelium and traced around to delineate the epithelial margin, leaving a hinge of 2 to 3 clock hours of intact margin, preferably at the 12 o’clock position. The loosened epithelium was then peeled back as a single hinged sheet using a dry Merocel sponge. More recently, we have used one arm of a modified Vannas scissors (ASICO) to delineate the epithelial margin and fashion a hinged epithelial flap. The modified Vannas scissors also allows for creative variations of the LASEK incision to be customized for different corneal types ( ).
After pushing aside the epithelial flap, the underlying stromal bed is ablated with an excimer laser. After ablation, an anterior chamber cannula is used to hydrate the stroma and float the epithelial flap over a layer of balanced salt solution. The epithelial flap is then replaced under intermittent irrigation and with careful attention to realignment of the epithelial flap margins using the previous marks. The epithelial flap is then allowed to dry for 2 to 3 minutes. If the epithelium appears healthy and attaches well, we keep it; otherwise, we remove it in light of our newer studies. The cornea is cooled with ice-chilled salt solution again for 15 seconds.
Topical steroids and antibiotic medications are applied, and a bandage contact lens (Soflens 66, Bausch & Lomb, or Acuvue Oasys, Johnson & Johnson) is placed. We could demonstrate significant benefits of using a bandage contact lens in terms of pain perception, visual recovery, and haze formation in a comparative study. The bandage contact lens is removed after complete reepithelialization (generally postoperative day 3 or 4); early removal or manipulation of the contact lens prior to postoperative day 3 risks peeling the epithelial flap with the contact lens. Oral analgesics are prescribed to be taken every 4 hours as needed.
From our experience, we have learned that our technique may not require specialized instruments but does necessitate several key steps for consistent epithelial flap creation and replacement. Pretreatment with several drops of 4% tetracaine prior to alcohol exposure helps to loosen the epithelium and reduce intraoperative discomfort. Placement of overlapping corneal marks is crucial to ensuring correct epithelial alignment and avoiding irregular epithelial placement and mismatch. We use an alcohol dispenser, but any optical zone marker with a barrel could be used to expose the epithelium to alcohol and avoid spillage. A modified Vannas scissors or a jeweler’s forceps to delineate the wound edge and locate the dissection plane and a dry, non-fragmenting cellulose sponge to peel the epithelial sheet are easily available instruments for creating the flap. The flap can be repositioned with an irrigating cannula under intermittent hydration, using the preplaced corneal marks as a guide. No overlap of the flap and wound edge has been observed that would have been attributable to stretching of the flap during peeling or overexpansion due to generous hydration.
We have described star-shaped, S-shaped, Z-shaped modifications of the epithelial sheet margins as possible variants of our technique.
Camellin Technique
In the Camellin technique a sharp, partial-thickness trephination of the epithelium is carried out prior to alcohol application: a preincision of the corneal epithelium is done to circumscribe the flap area and to allow the alcohol solution to penetrate under the flap using a dedicated trephine (J2900, Janach), which has a blunt section of 90 degrees for the formation of a hinge ( Fig. 19.3 ). A rotation of about 10 degrees is performed, repeating the maneuver two or three times while maintaining a constant pressure. Then 20% alcohol solution (96% pure alcohol in injectable distilled water) is instilled into a small holding well (Janach J2905) on the corneal surface for 30 seconds. The well serves two functions: holding the eye still and avoiding discharge of fluid. The surface is dried and rinsed thoroughly with balanced salt solution (BSS) and a final irrigation with an antihistamine to reduce the amount of histamine induced by the alcohol. Subsequently, the epithelium is detached with the short side of a dedicated epithelial detaching spatula (Janach J2910A). By making tiny movements almost perpendicular to the margin, the epithelial sheet is folded at the 12 o’clock position to keep it moist during the treatment. Before laser ablation, the longer side of this spatula is passed over the stromal surface to remove any debris. If necessary, the exposed stromal area may be enlarged by slightly stripping the epithelium in the periphery. Camellin has adjusted his PRK nomogram by reducing the preset values by 10% when treating myopia up to 10 D and by 20% for myopias of 10 D to 20 D, thus avoiding overcorrection. He advises protection of the flap with a masking fluid if smoothing is performed. The epithelial flap is returned after laser ablation with another spatula (Janach J2920A) and a soft contact lens is applied. Postoperatively, antibiotic and cortisone eye drops are administered for a few days, and a mild cortisone treatment is continued for up to a month. If complete reepithelialization has not taken place at postoperative day 3 or 4, a new lens is fitted for 3 more days. Camellin strongly points out the importance of a hypotonic solution, obtained by diluting alcohol in distilled water, for facilitating epithelial detachment.
The elliptical instruments developed by Lohmann are based on those conceived by Camellin and geared toward better accommodation of an elliptical ablation in the treatment of large astigmatism.
Vinciguerra Butterfly Technique
Decreased epithelial viability after alcohol exposure is a postoperative complication of standard LASEK that may prolong visual recovery and cause temporary reduced visual acuity and discomfort. Vinciguerra developed a modification of the standard approach to creating the epithelial flap that, by preserving the limbal connection of epithelial stem cells and limbal vascular connections, aims at increasing epithelial viability, thus reducing the occurrence of these complications.
In the Vinciguerra butterfly technique, a thin paracentral epithelial line, from 8 to 11 o’clock, is abraded with a specially designed spatula, and 20% alcohol in BSS is placed in contact with the cornea for 5 to 30 seconds. With the same spatula, the epithelium is separated from the Bowman layer, proceeding from the center to the periphery on both sides. A special retractor is used to move the two sheets of loose epithelium sideways toward the limbus and hold them in place. After drying the surface, excimer laser ablation is performed. Smoothing of the stromal surface with a hyaluronic acid masking solution (Laservis; Chemedica) is then carried out, followed by repositioning of the stretched epithelial flaps with the margins overlapping.
Azar Flap Technique
Our LASEK technique ( Fig. 19.2 ) evolved from PRK after alcohol-assisted epithelial removal. After application of topical 0.5% proparacaine (Ophthetic, Allergan, Inc.) and 4% tetracaine (formulated in a pharmacy), a lid speculum is applied. The cornea is then marked with overlapping 3-mm circles around the corneal periphery, simulating a floral pattern. An alcohol dispenser consisting of a customized 7- or 9-mm semi-sharp marker (ASICO) attached to a hollow metal handle serves as the reservoir for 18% alcohol. After 25 to 30 seconds, the ethanol is absorbed using an aspiration hole, followed by dry sponges (Weck-cel or Merocel, BVI). If necessary, the ethanol application may be repeated for an additional 10 to 15 seconds.
We then use ice-chilled, sterile salt solution to wash away any ethanol residues from the ocular surface and cool the cornea. Cooling the cornea to minimize postoperative pain and haze formation was originally described as early as 1994 for PRK.
Over time, the step of epithelial removal has been modified. Initially, one arm of a jeweler’s forceps was inserted under the epithelium and traced around to delineate the epithelial margin, leaving a hinge of 2 to 3 clock hours of intact margin, preferably at the 12 o’clock position. The loosened epithelium was then peeled back as a single hinged sheet using a dry Merocel sponge. More recently, we have used one arm of a modified Vannas scissors (ASICO) to delineate the epithelial margin and fashion a hinged epithelial flap. The modified Vannas scissors also allows for creative variations of the LASEK incision to be customized for different corneal types ( ).
After pushing aside the epithelial flap, the underlying stromal bed is ablated with an excimer laser. After ablation, an anterior chamber cannula is used to hydrate the stroma and float the epithelial flap over a layer of balanced salt solution. The epithelial flap is then replaced under intermittent irrigation and with careful attention to realignment of the epithelial flap margins using the previous marks. The epithelial flap is then allowed to dry for 2 to 3 minutes. If the epithelium appears healthy and attaches well, we keep it; otherwise, we remove it in light of our newer studies. The cornea is cooled with ice-chilled salt solution again for 15 seconds.
Topical steroids and antibiotic medications are applied, and a bandage contact lens (Soflens 66, Bausch & Lomb, or Acuvue Oasys, Johnson & Johnson) is placed. We could demonstrate significant benefits of using a bandage contact lens in terms of pain perception, visual recovery, and haze formation in a comparative study. The bandage contact lens is removed after complete reepithelialization (generally postoperative day 3 or 4); early removal or manipulation of the contact lens prior to postoperative day 3 risks peeling the epithelial flap with the contact lens. Oral analgesics are prescribed to be taken every 4 hours as needed.
From our experience, we have learned that our technique may not require specialized instruments but does necessitate several key steps for consistent epithelial flap creation and replacement. Pretreatment with several drops of 4% tetracaine prior to alcohol exposure helps to loosen the epithelium and reduce intraoperative discomfort. Placement of overlapping corneal marks is crucial to ensuring correct epithelial alignment and avoiding irregular epithelial placement and mismatch. We use an alcohol dispenser, but any optical zone marker with a barrel could be used to expose the epithelium to alcohol and avoid spillage. A modified Vannas scissors or a jeweler’s forceps to delineate the wound edge and locate the dissection plane and a dry, non-fragmenting cellulose sponge to peel the epithelial sheet are easily available instruments for creating the flap. The flap can be repositioned with an irrigating cannula under intermittent hydration, using the preplaced corneal marks as a guide. No overlap of the flap and wound edge has been observed that would have been attributable to stretching of the flap during peeling or overexpansion due to generous hydration.
We have described star-shaped, S-shaped, Z-shaped modifications of the epithelial sheet margins as possible variants of our technique.
Camellin Technique
In the Camellin technique a sharp, partial-thickness trephination of the epithelium is carried out prior to alcohol application: a preincision of the corneal epithelium is done to circumscribe the flap area and to allow the alcohol solution to penetrate under the flap using a dedicated trephine (J2900, Janach), which has a blunt section of 90 degrees for the formation of a hinge ( Fig. 19.3 ). A rotation of about 10 degrees is performed, repeating the maneuver two or three times while maintaining a constant pressure. Then 20% alcohol solution (96% pure alcohol in injectable distilled water) is instilled into a small holding well (Janach J2905) on the corneal surface for 30 seconds. The well serves two functions: holding the eye still and avoiding discharge of fluid. The surface is dried and rinsed thoroughly with balanced salt solution (BSS) and a final irrigation with an antihistamine to reduce the amount of histamine induced by the alcohol. Subsequently, the epithelium is detached with the short side of a dedicated epithelial detaching spatula (Janach J2910A). By making tiny movements almost perpendicular to the margin, the epithelial sheet is folded at the 12 o’clock position to keep it moist during the treatment. Before laser ablation, the longer side of this spatula is passed over the stromal surface to remove any debris. If necessary, the exposed stromal area may be enlarged by slightly stripping the epithelium in the periphery. Camellin has adjusted his PRK nomogram by reducing the preset values by 10% when treating myopia up to 10 D and by 20% for myopias of 10 D to 20 D, thus avoiding overcorrection. He advises protection of the flap with a masking fluid if smoothing is performed. The epithelial flap is returned after laser ablation with another spatula (Janach J2920A) and a soft contact lens is applied. Postoperatively, antibiotic and cortisone eye drops are administered for a few days, and a mild cortisone treatment is continued for up to a month. If complete reepithelialization has not taken place at postoperative day 3 or 4, a new lens is fitted for 3 more days. Camellin strongly points out the importance of a hypotonic solution, obtained by diluting alcohol in distilled water, for facilitating epithelial detachment.
The elliptical instruments developed by Lohmann are based on those conceived by Camellin and geared toward better accommodation of an elliptical ablation in the treatment of large astigmatism.
Vinciguerra Butterfly Technique
Decreased epithelial viability after alcohol exposure is a postoperative complication of standard LASEK that may prolong visual recovery and cause temporary reduced visual acuity and discomfort. Vinciguerra developed a modification of the standard approach to creating the epithelial flap that, by preserving the limbal connection of epithelial stem cells and limbal vascular connections, aims at increasing epithelial viability, thus reducing the occurrence of these complications.
In the Vinciguerra butterfly technique, a thin paracentral epithelial line, from 8 to 11 o’clock, is abraded with a specially designed spatula, and 20% alcohol in BSS is placed in contact with the cornea for 5 to 30 seconds. With the same spatula, the epithelium is separated from the Bowman layer, proceeding from the center to the periphery on both sides. A special retractor is used to move the two sheets of loose epithelium sideways toward the limbus and hold them in place. After drying the surface, excimer laser ablation is performed. Smoothing of the stromal surface with a hyaluronic acid masking solution (Laservis; Chemedica) is then carried out, followed by repositioning of the stretched epithelial flaps with the margins overlapping.
Alternatives to Alcohol-Assisted Epithelial Removal
To avoid the use of alcohol, first, McDonald developed a technique that uses microkeratome suction and a methylcellulose gel to create the epithelial sheet. Then, Pallikaris developed a mechanical device similar to the microkeratomes used for the flap preparation in LASIK that separates the epithelium from the stroma. He called his technique epi-LASIK . More recently, two modifications of surface ablation techniques have been described: trans-epithelial PRK and epi-Bowman keratectomy . With those latter techniques, the epithelium is destroyed and cannot be replaced, rendering them variants of PRK rather than LASEK. They are nevertheless briefly discussed in this chapter to provide an up-to-date overview of alternative ways to removing the epithelium without alcohol or other chemicals.
Epi-LASIK
Introduction
Epi-LASIK refers to an alternative surgical approach for epithelial separation by mechanical means. With this technique, the epithelial separation is performed using an instrument initially designed in the University of Crete to operate similarly to a microkeratome. The first commercially available device underwent development improvements to achieve epithelial separation by the forward movement of a disposable, oscillating polymethylmethacrylate (PMMA) block ( Figs. 19.4 A and B ). Histologic studies of specimens obtained with this device have shown that the basement membrane remains intact, whereas the sheet also includes a small portion of the upper part of the Bowman layer with a thickness that ranges between 300 and 1500 nm in different specimens ( Fig. 19.4 C ).
Subsequently, different companies marketed similar devices called epikeratomes ( ). Although the original idea of epi-LASIK was to avoid the use of alcohol, Camellin has described a modification with an alcohol pretreatment before the use of an epikeratome.
The Original Surgical Procedure
The operative eye is anesthetized with three drops of topical tetracaine hydrochloride 0.5% applied every 5 minutes before the procedure and is prepared with povidone-iodine to be covered with a sterile drape. The epithelial surface may be marked with two concentric circles crossed by eight radial arms with a specially designed marker (epi-LASIK marker, Duckworth & Kent). Before the epithelial separation, the cornea is cooled using drops of prechilled BSS for 30 seconds. A Barraquer tonometer ensures adequate suction before the separation and a few drops of BSS acts as lubricant for the operative cornea. Fig. 19.5 depicts the pass of the separator and the following steps. Once the separator reaches its final position, the suction is released and the device is removed from the eye. With the use of either a moistened Merocel sponge or a metallic spatula (Duckworth & Kent) the epithelial sheet is reflected nasally to reveal the corneal stroma to be ablated.
Immediately after the ablation, the procedure of corneal cooling is repeated and the epithelial sheet is replaced with the aid of the metallic spatula. Its replacement is often achieved with a single movement. Any inward or outward folds of its edges are restored with the use of an anterior chamber irrigation cannula under constant irrigation. Once the epithelial sheet is stuck to the underlying stroma, a therapeutic contact lens is applied to the operative eye.
Postoperative Care
All patients are prescribed eye drops of diclofenac sodium for 2 days and combined eye drops of tobramycin–dexamethasone (Tobradex, Alcon Laboratories) q.i.d. until removal of the bandage contact lens, which takes place at postoperative day 4 or 5. Removal of the contact lens before complete epithelial healing may dislocate the epithelial sheet. After removal of the lens, the patients receive fluorometholone eye drops (FML, Allergan) q.i.d. on a tapered dose for 5 weeks. Artificial tears are prescribed as needed.
Epi-LASIK Clinical Results
Clinical results of epi-LASIK are excellent in terms of both refractive and visual outcomes and suggest that epi-LASIK provides a safe and efficient alternative technique for photorefractive corrections on the stromal surface ( Table 19.1 ).
| Study | Number of Eyes | Follow-up | UDVA | Diopters Within Attempted Correction | Loss of CDVA/Rate of Haze formation |
|---|---|---|---|---|---|
| Pallikaris et al. | 44 | 1 day | 38% with ≥ 20/40 | ||
| Day of reepithelialization | 34% with ≥ 20/25 85% with ≥ 20/40 | ||||
| 1 month | 65% with ≥ 20/25 95% with ≥ 20/40 | 48% within ± 0.5 95% within ± 1.0 | 44% haze | ||
| 3 months | 92% with ≥ 20/25 96% with ≥ 20/40 | 78% within ± 0.5 100% within ± 1.0 | 0% lost > 1 line CDVA 41% haze | ||
| Katsanevaki et al. | 234 | 1 day | 28% with ≥ 20/20 53% with ≥ 20/40 | ||
| Day of reepithelialization | 34% with ≥ 20/20 78% with ≥ 20/40 | ||||
| 1 month | 54% with ≥ 20/20 95% with ≥ 20/40 | 60% within ± 0.5 86% within ± 1.0 | 25% lost > 1 line CDVA 52% with haze | ||
| 3 months | 81% with ≥ 20/20 99% with ≥ 20/40 | 78% within ± 0.5 95% within ± 1.0 | 38% haze | ||
| 1 year | 86% with ≥ 20/20 100% with ≥ 20/40 | 80% within ± 0.5 97% within ± 1.0 | 0% lost > 1 line 14% haze |
Introduction
Epi-LASIK refers to an alternative surgical approach for epithelial separation by mechanical means. With this technique, the epithelial separation is performed using an instrument initially designed in the University of Crete to operate similarly to a microkeratome. The first commercially available device underwent development improvements to achieve epithelial separation by the forward movement of a disposable, oscillating polymethylmethacrylate (PMMA) block ( Figs. 19.4 A and B ). Histologic studies of specimens obtained with this device have shown that the basement membrane remains intact, whereas the sheet also includes a small portion of the upper part of the Bowman layer with a thickness that ranges between 300 and 1500 nm in different specimens ( Fig. 19.4 C ).
Subsequently, different companies marketed similar devices called epikeratomes ( ). Although the original idea of epi-LASIK was to avoid the use of alcohol, Camellin has described a modification with an alcohol pretreatment before the use of an epikeratome.
The Original Surgical Procedure
The operative eye is anesthetized with three drops of topical tetracaine hydrochloride 0.5% applied every 5 minutes before the procedure and is prepared with povidone-iodine to be covered with a sterile drape. The epithelial surface may be marked with two concentric circles crossed by eight radial arms with a specially designed marker (epi-LASIK marker, Duckworth & Kent). Before the epithelial separation, the cornea is cooled using drops of prechilled BSS for 30 seconds. A Barraquer tonometer ensures adequate suction before the separation and a few drops of BSS acts as lubricant for the operative cornea. Fig. 19.5 depicts the pass of the separator and the following steps. Once the separator reaches its final position, the suction is released and the device is removed from the eye. With the use of either a moistened Merocel sponge or a metallic spatula (Duckworth & Kent) the epithelial sheet is reflected nasally to reveal the corneal stroma to be ablated.
