Confocal and Electron Microscopic Studies of Laser Subepithelial Keratomileusis(LASEK) in the White Leghorn Chick Eye

Abstract

To evaluate the effect of 20% alcohol on the white leghorn chick cornea and to determine the confocal and electron microscopic findings of laser subepithelial keratomileusis surgery in the white leghorn chick corneal model. Method: Laser subepithelial keratomileusis surgery was performed on chick corneas and the morphologic changes were examined by transmission electron microscopy. Chick corneas were exposed to 20% alcohol for 30 and 45 seconds or 1 and 2 minutes (5 chicks per group) to evaluate the effect on the corneal epithelium. Photorefractive keratectomy using either mechanical or 20% alcohol-assisted debridement (5 chicks per group) was also performed. Keratocyte and epithelial cell deaths were analyzed 4 hours after surgery using terminal deoxynucleotidyl transfermediated biotin-dexoyuridine 5-triphosphate nick-end labeling (TUNEL) staining and transmission electron microscopy. Results: Exposure of the corneal epithelium to 20% alcohol for 30 seconds or longer allowed reproducible separation of epithelial flaps in white leghorn chick eyes. Transmission electron microscopy immediately after alcohol treatment showed that exposure to 20% alcohol for 30 seconds or less had minimal adverse effects on the corneal epithelium. The TUNEL staining of corneas obtained 4 hours after surgery revealed TUNEL-positive cells in the central superficial stroma and more abundantly in the peripheral superficial stroma around the epithelial flap margin and in the epithelial flap itself, particularly in the basal epithelial layer. Transmission electron microscopy showed similar evidence of apoptosis in the epithelium and anterior stroma. Conclusions: The white leghorn chick eye seems to be a reasonable model for laser subepithelial keratomileusis surgery. Treatment with 20% alcohol for 30 seconds results in reproducible epithelial flap creation in the chick cornea and in relatively low levels of stromal and epithelial cell death after surgery.

Comparison of corneal wound-healing response in photorefractive keratectomy and laser-assisted subepithelial keratectomy

“…However, with higher corrections, a significant increase in TUNEL positive cells was seen in the PRK group. Our study is in agreement with that of Lee et al, 17 who showed evidence of superficial keratocyte apoptosis in the central stroma of the leghorn chick cornea 4 hours after PRK. In contrast, 4 hours following LASEK, less apoptotic cells were found adjacent to the ablated stroma.…”

Effectiveness of laser-assisted subepithelial keratectomy to treat residual refractive errors after laser in situ keratomileusis

“…[24][25][26][27] By maintaining the integrity of the epithelial layer, LASEK theoretically reduces the activation of abnormal stromal wound healing and resultant haze formation due to the barrier function of the epithelium, which reduces migration of cytokines into the stroma; the integrity of the basement membrane, which may allow epithelial regeneration without scarring; and the viability of the basal epithelial cell, which may minimize epithelial proliferation. 24,28,29 This may in part explain why our patients had a lower incidence of haze formation after LASEK retreatment than after PRK retreatment. Similar to the results in our study, Li et al 30 found that LASEK retreatment in eyes with myopic regression after LASIK resulted in improved UCVA without significant intraoperative or postoperative complications.…”

Development of late-onset subepithelial corneal haze after laser-assisted subepithelial keratectomy with prophylactic intraoperative mitomycin-C

“…30,31 The wound modulating properties of the epithelial flap were observed in white leghorn chick eyes that had LASEK. 32 Less keratocyte apoptosis was seen in the central superficial stroma than in the peripheral stroma, perhaps because the epithelial flap served as a plug and barrier against the influx of tear cytokines into the central stroma. An albino rabbit model comparing LASEK and PRK showed that at higher ablations (À7.00 D), LASEK induced less keratocyte apoptosis, myofibroblast transformation, and chondroitin sulfate synthesis.…”