Electron microscopic and immunohistochemical examination of scarred human cornea re-treated by excimer laser.

Purpose: To elucidate differences, at the macromolecular level, in corneal tissue subjected to repeated argon fluoride excimer treatment.

Methods: A light microscopic, electron microscopic, and immunohistochemical study was performed on a scarred human cornea.

Results: Keratocytes were enlarged with an expanded endoplasmic reticulum and exhibited a fibroblastic appearance. Amorphous material was observed extracellularly. Collagen fibrils exhibited a disordered arrangement while banding patterns and diameter were normal. Immunohistochemical investigation of several collagen types, of collagen-associated proteoglycans, and of basement membrane components demonstrated an enhanced immunoreactivity of all of them in the scarred area. Type V collagen was found as a normal component of the epithelial basement membrane whereas types I and III collagen were present beneath Bowman's layer. Excimer-laser-treated sections revealed considerably stronger subepithelial staining for collagen types I, III, IV, and V. Laminin-1, a typical component of basement membranes, was detectable throughout the scarred tissue. The small proteoglycans decorin and fibromodulin accumulated in a patch-like manner in the scarred tissue below the epithelium, whereas biglycan was expressed by the epithelium and throughout the stroma. Lumican was expressed most strongly by the epithelium and rather equally distributed in the excimer-laser-treated and in the normal stroma.

Conclusion: Effects of argon laser treatment of the cornea must be regarded as a process acting over many months. Intra- and extracellular structures and components are involved and influence the unpredictable shape of the corneal architecture.