CONTROL OF CORNEAL HYDRATION AND TRANSPARENCY

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The proposed research is designed to investigate two models of stress in the corneal endothelium and to establish on a quantitative basis the nature of the ion transport mechanisms in this cell layer are responsible for maintaining corneal hydration and transparency. A study of the effects of ultraviolet light on the corneal endothelium will seek to determine what is the primary site of injury that results in an increase in corneal hydration and marked changes in the appearance of the endothelium. It is postulated that an oxidative mechanism, provoked by the formation of free radicals following absorption of the high energy photons, causes damage to enzymes or membrane proteins and lipids. Structural changes that follow may result from alteration of cytoskeletal elements or from release of chemotactic factors that cause invasion of leukocytes that become attached to the endothelium. The hypothesis will be tested by assessing metabolic changes after UV exposure and the effects of changes in anti-oxidants and detoxifying or protective enzymes on the corneal response to UV. Defining the nature and origin of the structural changes will entail examination by a number of microscopy techniques, modification of the inflammatory response, and in vitro systems for testing chemotaxis and leukocyte recruitment. The diabetic study will seek in an animal model the basis for the failure of diabetic patients to withstand intraocular surgery without more severe corneal swelling than other patients. It is postulated that the endothelium is compromised by the disease in a manner which reduces the effectiveness or capacity of defensive or maintenance mechanisms, such that the pump or barrier functions are more vulnerable to subsequent insults. The effects of hyperglycaemia on the concentrations of sorbitol and inositol and upon inositol metabolism will be measured, as these may regulate protein kinase and Na+-K+ ATPase activities, and endothelial morphology and cell pattern will be followed to detect weakening of the barrier characteristics. Additional stresses and inhibitors of aldose reductase will be used to identify the key sites of damage. The study of ion transport in the endothelium will focus on the absolute values of fluxes and the extent of coupling in order to provide sound data for assessment of postulated mechanisms.