Corneal ablation in rabbits using an infrared (2.9-microns) erbium: YAG laser

The authors used a 2.9-microns infrared erbium:YAG (ER:YAG) laser to ablate the central corneas (a 3.5-mm wide, 180-microns deep area) of ten albino rabbits. In group 1 (10 eyes), the central epithelium was removed by mechanical scrubbing to ablate the anterior stroma. In group 2 (10 eyes), a central anterior corneal cap was removed to ablate the midstroma. In group 1, epithelial wound healing occurred in 2 to 3 days. A mild anterior haze was observed with the slit lamp, but it gradually cleared in most eyes of both groups. Histologic specimens were obtained immediately and at 2 and 6 months after ablation for light and transmission and scanning electron microscopy. This acute histopathologic study did not show any endothelial damage even after ablations at 300-microns depth, although there was thermal damage more prominent at the borders of the ablated area for an extension of 40 microns. After 2 months, in the group 1 eyes, the regenerated epithelium appeared normal except for a thickening at the margins of the ablated area. Six months postoperatively there was still epithelial thickening at the margins of the remodeled zone. The basement membrane was present with anchoring filaments and hemidesmosomes. The healing of the anterior (group 1) and midstroma (group 2) occurred with some degree of disorganization of the lamellae and an increase in the population of keratocytes. The density of keratocytes at the ablated areas at 6 months was reduced in comparison with the 2-month observation. By photokeratoscopy, the corneas were smooth and slightly flattened. The authors conclude that corneal ablation using an ER: YAG laser at 2.9 microns may meet the criteria for photorefractive keratectomy (PRK).