Nowadays excimer laser surgery is one of the most popular procedure in ophthalmology. Thousand of patients are operated year by year in US to correct different refractive errors.(1) In this field, LASIK and PRK have become the most commonly performed surgical procedures due to they are safe and effective, but in both of them there are some disadvantages. In the case of PRK, haze, post operated pain and low visual recovery are some of the commonly complications. On the other hand, LASIK also has disadvantages, such as flap related complications (intra and post operated), interface related complications and ectasia post lasik.(2)
LASEK (Laser epithelial keratomileusis) could avoid all those disadvantages and plus, combine the advantages of PRK and LASIK.
The history of LASEK began in 1996 , when the first LASEK procedure was performed at the Massachusetts Eye and Ear Infirmary by Azar, DT, (3) but was Massimo Camellin who introduced the term LASEK and popularized this procedure(4)(5)(6)
There are different techniques for this procedure, but basically consist in produce an epithelial detachment with an alcohol diluted solution (18-20%). Once the alcohol solution is rinsed, epithelium is removed and a flap is folded creating a nasal or superior hinge. Later, laser ablation is performed and epithelium is replaced on the stroma with special attention to achieve correct alignment to avoid future complications. Finally, topical steroids and antibiotic are applied and a soft contact lens is placed. The soft contact lens has to be removed after a complete re-epithelialization (3 or 4 days). (7)(8)(9)
After instillation of topical ophthalmic anesthesia, a notched microtrephine is used to create an epithelial incision (with a 90° hinge at 12:00). An alcohol 18% ethanol solution (using distilled water rather than balanced salt solution) is instilled and held for 20 or 30 seconds. The surface of the eye is then rinsed with diclofenac sodium. A microhoe is then used to detach the flap edge and to shift it toward the 12:00 position. Laser ablation is performed and then the epithelium is then repositioned and a soft contact lens is placed on the cornea for 3 to 4 days. Postoperatively, antibiotic and cortisone eye drops are administered for a few days, and a mild cortisone treatment is continued for up to a month.(10)
After application of topical 0.05% proparacaine (Ophthetic; Allergan, Inc., Irvine, CA) and 4% tetracaine (formulated in the Massachusetts Eye and Ear Infirmary pharmacy), a lid speculum is applied. The cornea is then marked with overlapping 3mm circles around the corneal periphery, simulating a floral pattern. An alcohol dispenser consisting of a customized 7 or 9mm semi-sharp marker (ASICO, Westmont, IL) attached to a hollow metal handle serves as the reservoir for 18% alcohol. After 25–30s, the ethanol is absorbed using an aspiration hole followed by dry sponges (Weckcel or Merocel). If necessary, the ethanol application may be repeated for an additional 10–15s. Epithelial removal is performed with an arm of a modified Vannas scissors (ASICO) to delineate the epithelial margin and fashion a hinged epithelial flap. The modified Vannas scissors also allow 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 2–5min. Topical steroids and antibiotic medications are applied, and a bandage contact lens placed. The bandage contact lens is removed after complete reepithelialization (generally postoperative day 3 or 4).(7)(15)(16)
Vinciguerra (butterfly technique)
In this technique, with a Vinciguerra spatula (ASICO, Westmont IL), a thin abrasion (0.75 mm) is performed on the paracentral cornea from the 8:00 to 11:00 positions, and 20% alcohol in BSS is placed in contact with the cornea for 5–30 seconds. With the same spatula, the epithelium is separated from Bowman’s layer, proceeding from center to periphery on both sides. Vinciguerra LASEK butterfly protector/retractor (ASICO) 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 with a hyaluronic acid masking solution (Laservis; Cheme- dica, Munchen, Germany) is then carried out, followed by repositioning of the stretched epithelial flaps with the margins overlapping. (11)(12)
This is an alcohol-free McDonald technique, the epithelium is marked and then coated with GenTeal® gel. Trephination of the cornea is then performed. Scoring of the epithelium down to Bowman’s layer (a distance of 1–2 mm) is performed using a 2.25 rounded knife (ASICO). Ten drops of 5% NaCl ophthalmic solution are applied to the corneal epithelium (to stiffen the epithelium) and then blotted dry with eye spears. A microkeratome head (upside down) is placed on the eye and the stalk/stem is held by a surgical assistant (as the surgeon must use both hands to continue operating); suction is then applied. A cannula is then slipped under the epithelium and used as a fulcrum to sweep and to loosen the epithelium. Suction is then re- leased and GenTeal® gel is then injected under the loosened epithelium. A LASEK flap is then created via the Vinciguerra butterfly technique. Using Vannas scissors, a cut is made through the center of the sheet of epithelium and the two halves of the sheet are reflected to the side. Alternatively, the sheet of epithelium may be quadrisected rather than bisected. An eye spear is then used to remove the gel from Bowman’s and excimer laser ablation is applied. The epithelium is then replaced and a bandage contact lens is placed. (9)(13)(14)
In my case is a modified of Azar technique. After topical anesthesia is applied and lid speculum is correctly collocated, the cornea is marked (just one or two marked are necessary) and an alcohol dispenser is attached on the cornea surface, I prefer to use a PRK marker of 8 mm. 20% Alcohol solution is applied for 40 seconds and then is absorbed using a Merocel dry sponges. This procedure could be repeated if you consider that epithelium is still attached to the Bowman Membrane, in this case, the time advised is 10 seconds. A LASIK spatula is inserted under the epithelium to delineate the epithelial margin and then with a wet Merocel sponge, epithelium detachment is performed leaving a hinge. Epithelium removal is easy and reliable, starting by the periphery and always trying to protect the center of the stromal bed in order to avoid an overcorrection produced for the stromal bed dryness. Surface is dried and ablation applied. A generous irrigation is advisable and epithelium replacement is done with a merocel sponge too, irrigating again to avoid detritus on the interfase and ensure a correct alignment of flap. I like to wait three minutes to achieve a correct dryness. Antibiotic and steroids drops and then a soft contact lens. In my personal opinion, specialized instruments are not necessary, but we must to be very careful with the handling of the flap. Otherwise, remember that the possibility to convert in PRK always is a possibility when epithelium flap complications appears.
Advantages and Disadvantages
- No free cap
- No incomplete flap
- No bottonhole
- No flap striae / wrinkles
- No flap infection
- No flap traumatic dislocation
- No epithelial ingrowth
- No diffuse lamellar keratitis
- Lower risk of ectasia
- Post-operative pain
- Post-operative discomfort
- Slow visual rehabilitation
- Subepithelial haze
- Higher risk of persistent epithelial defect
- Higher risk of microbial keratitis
LASEK & PRK
Hashemi et al are performed a prospective, randomized and paired comparison between LASEK and PRK for myopia less than -6.50 diopters and reported similar predictability, efficacy, safety, and patient satisfaction to PRK in the treatment of low to moderate myopia.(26). Also Lee et al compared LASEK and PRK, in this case for low to moderate myopia (–3.00 to –6.50 diopters) in 27 patients and reported during 3 month follow-up, there were no significant between-eye differences in epithelial healing time, UCVA, or refractive error. However, he reported that LASEK-treated eyes had lower postoperative pain scores and corneal haze scores than PRK-treated eyes. Finally, is this study seventeen patients (63%) preferred the LASEK procedure(27). On the other hand, Litwak et al found less discomfort in PRK eyes than LASEK eyes in 25 patients studied.(32) An interesting meta-analysis was performed by Cui et al comparing PRK and LASEK according to the available data, they reported there is no difference between PRK and LASIK for correcting myopia from 0 to -9.0 D. This study mainly focused on the comparison of the early, mid-term and mid-long term results of the two methods.(28). Even though some authors found more advantages in LASEK than PRK, today we need more studies to know if there is a real and significant advantage between these technique.
LASEK & LASIK
Tobaigy et al matched each LASEK-treated eye to a LASIK-treated eye using specific criteria. Finally 122 LASEK eyes were matched with 122 LASIK eyes. This group concluded, although there were some differences in the visual and refractive results favoring LASEK, they were not clinically significant. Both procedures seemed safe, effective, and predictable for the treatment of low and moderate myopia (2). Zhao et al found in their meta-analysis that there were no significant differences in visual and refractive outcomes between the LASEK and LASIK for low to moderate myopia in the midterm and long-term follow-up, and suggests new randomized and prospective studied to know the benefits of this technique (29) Kaya et al reported the results of LASEK and LASIK in a prospective study for myopia of less than -6.0 D. Based on 6-month results, they found no statistical difference in UCVA, BSCVA, and spherical and cylindrical refractive error between the groups and considered LASEK an alternative for LASIK. (30) Also Kim compared the visual and refractive results of LASEK and LASIK for high myopia in 470 eyes up to 1 year post-operatively. They found an UCVA of 20/25 was achieved in 83% of the eyes that underwent LASIK compared with 76% that underwent LASEK. More eyes lost more than one line in LASEK (14.3%) than LASIK (1.2%). This group concluded that LASIK provided superior and more favorable results for high myopia.(31) In summary, both techniques are safe and effective, regardless post-operated difference exposed above. Finally, every surgeon has to take a decision based in the characteristic of the patient such as activities and lifestyle, cornea thickness and requirement of visual rehabilitation.
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