Experimental and computational investigation of corneal transport properties
Description
Corneal transparency, on which our vision depends, is a function of the complex physiological, structural, and biochemical interaction of the limiting membranes with the highly organized stromal tissue. Membrane transport of solutes and water provides necessary nutrients, removes waste, and maintains intrastromal pressure The primary goal of this investigation was to characterize the response of the corneal transport system to NaCl osmotic perturbations. A secondary goal was the characterization of the serendipitous discovery of an anomalous corneal swelling response following mechanical epithelial removal To retrieve corneal membrane transport properties from osmotically induced thickness changes, one-dimensional differential and integral models of the corneal transport system, including unstirred water layers were developed. Previous epithelial and newly generated endothelial osmotic perturbation experiments were matched with the computer models. Software was designed to track intrastromal reflective structures and to quantify the anomalous swelling of the anterior cornea following mechanical debridement (under silicone oil) of the epithelium It was shown that unstirred layers did not interfere with membrane parameter extraction, that small ($\pm$15 mOsm) NaCl perturbations elicited a volume regulatory response from the corneal endothelium, and that removal of the epithelium resulted in an anomalous anterior fluid shift Confidence in corneal membrane transport parameters derived by numerical fitting of the thickness response to osmotic shocks has been improved by the characterization of unstirred layer effects. The active response of the endothelial membrane to small perturbations of NaCl demonstrates the existence of a new control mechanism. The anterior fluid shift secondary to mechanical debridement suggests a new etiology for the acute edema following injury to tissue. It is postulated that mechanical damage to the epithelium releases proteases that lyse stromal ground substance subsequently increasing local osmotic pressure