Histopathology of corneal wound healing after photorefractive keratectomy in rabbit eyes.

esults of excimer laser photorefractive kera-tectomy (PRK) for low and moderate myopia are clinically acceptable. 1,2 After PRK, slight changes in corneal transparency in the ablation zone or some superficial corneal problems can be observed postoperatively, no matter the excimer laser employed. Some reports describe anterior wound healing after excimer laser keratectomy. Tuft et al 3 and Marshall et al 4 used a circular mark to create cylindrical excisions with vertical margins in rabbits and monkeys. They observed subepithelial opacification with slit-lamp microscopy and new col-lagen formation histopathologically. McDonald and colleagues 5 used a constricting, motorized diaphragm that created an excision with multi-stepped sloping margins in rabbits and monkeys. They observed some clear corneas and some opaque corneas shortly after surgery. Del Pero and colleagues 6 used progressively smaller circular masks to create a myopic ablation in monkeys and humans, reporting a subepithelial speckled haze clinically and histopathologically. Obata 7 used a scanning delivery system to ablate rabbit corneas; the ablat-ed surface was observed to be smooth and uniform. Stromal collagen adjacent to the pseudomembrane showed normal structure. MATERIALS AND METHODS A total of eight new Zealand white rabbits were used in this study. The animals were anesthetized with intramuscular injections of ketamine and xylazine after which topical proparacaine was instilled into the cornea. The corneal epithelium was then removed with a Paton spatula. The eye was positioned under the laser, using the pupil as the center for ablations. Neither blowing nor aspirating devices were used during the laser procedure. A 193 nm argon-fluoride excimer laser (Nidek EC-5000, Nidek, Japan) was used. This system incorporates an innovative scanning method for excimer laser delivery. Ten pulses of a rectangular-shaped laser beam are integrated into six directions by rotation. The excimer was calibrated before each use by ablating polymethylmethacrylate blocks. For all ablations, the average fluence was 173.8mJ/cm 2 with a repetition rate of 30 Hz and an ablation zone diameter of 5.5 mm. Ablation depth was a maximum of 90 µm. Rabbits treated with the laser were examined with a slit-lamp microscope by an independent ophthalmologist. All rabbits were killed with an overdose of barbiturate 2 months after surgery. Enucleated whole eyes were fixed with 10% formalin for 24 hours. Corneal buttons were excised, following dehydration in graded alcohol. Samples were embedded in paraffin wax. The serial sections were cut at 6 mm thickness , for 60 slides, and stained with …