CORNEAL RESPONSE TO RIGID CONTACT-LENS WEAR

Three adult rhesus monkeys were subjected to 2 and 24 h of polymethylmethacrylate (PMMA) contact lens wear. The induced corneal changes were examined with an EM. Mild epithelial edema as well as early degenerative cell changes were present already after 2 h wear. Rigid lens wear for 24 h produced more severe edema and cell alterations together with premature cell loss and ultimately, in areas of lens bearing, corneal denuding. Only the monkeys wearing contact lenses for 24 h had significant stromal swelling, which was primarily evident in the posterior region, while the anterior limiting lamina remained unaffected. The stromal swelling was patchy and mainly around keratocytes and between lamellae, while fluid within the lamellae was evident only occasionally in posterior stroma. Changes among keratocytes were evident, especially posteriorly, where reaction was frequently severe. Endothelial reaction was restricted to a limited fluid uptake in the 24 h wear experiment. There was in an apparent loosening of the endothelial adhesion to the posterior limiting lamina. Apparently, the edematous epithelium undergoes cell shrinkage and flattening, which is compensated for by an uptake of fluid. The uptake of fluid maintains the overall normal thickness of the epithelium. The normal thickness of edematous epithelium was shown by pachometry. Apparently, stromal edema in the [human] contact lens wearer is a result of a relative loss of endothelial function, leading to a swelling that moves in a posterior to anterior direction.