Histology after lamellar keratoplasty and corneal excimer laser ablation

PURPOSE: To correlate clinical and histological findings after lamellar ker atoplasty, phototherapeutic keratectomy, and application of a donor lenticu le on a human cornea. METHODS: A cornea was obtained during penetrating keratoplasty. The specime n was fixated, dehydrated and embedded in Epon resin. The tissue was cut in 0.5-mu m-thick semi-thin sections, stained with toluidine blue, and studie d with light microscopy. RESULTS: The central part of the photoablated cornea, which was covered by the donor lenticule, did not differ from a normal cornea. Peripherally a ha zy ring was found clinically. Histology showed an irregular epithelium. Whe re it was thickened, the epithelium was hyperplastic and showed an increase d number of cell layers. in the hazy region, Bowman's layer was absent, ind icating that the donor lenticule did not cover this part of the photokerate ctomized cornea. The anterior-most part of the corneal stroma was vacuolize d and contained amorphous extracellular material; swollen keratocytes were present in this region. Beneath this layer, collagen lamellae were wavy and interwoven and keratocytes were increased in number, appeared swollen, and some had assumed an atypical shape. Peripheral to the haze, the cornea was clear. Histologically, the epithelium was irregular and hyperplastic, Bowm an's layer was absent, and stromal collagen lamellae were abnormally organi zed, but no vacuolization was found. Conclusions: The formation of haze after excimer laser photokeratectomy can be minimized if the ablated stroma is covered by a corneal lenticule.