From Oxygen to Oedema

Wear of low-oxygen-transmissible soft contact lenses swells the cornea significantly, even during open eye. Although oxygen-deficient corneal edema is well documented, much of it by research here at Berkeley, quantitative description is not available. We present a biochemical description of the human cornea that quantifies the oxygen-deficient swelling of the cornea through the coupled tranport of water, salt, and respiratory metabolites. Aerobic and anaerobic consumption of glucose, as well as pH buffering, are incorporated in a seven-layer (aqueous chamber, endothelium, stroma, epithelium, post-lens tear film, contact lens, and pre-lens tear film) corneal model. Corneal swelling is predicted from coupled transport of water, dissolved salts, and especially metabolites, along with membrane resistances at the endothelim and epithelium. At the endothelium, the Na+/K+ ATPase electrogenic channel actively transports bicarbonate ion from the stroma into the anterior chamber. As captured by the Kedem-Katchalsky membrane-transport formalism, the active bicarbonate-ion flux provides the driving force for fluid pump-out needed to match the leak-in swelling tendency of the stroma. Increased lactate-ion production during hypoxia lowers the pump-out rate requiring the stoma to swell to a higher water content. Concentration and hydration profiles are predicted for glucose, water, oxygen, and carbon dioxide, and hydronium, lactate, bicarbonate, sodium, and chloride ions. Although the bicarbonate-ion pump at the endothelium drives bicarbonate into the aqueous humor, we predicat a net flux of bicarbonate into the cornea that prevents over acidosis. For the first time, we predict swelling behavior upon soft-contact-lens wear from fundamental biophysico-chemical principles. We also sucessfully predict that hypertonic tear osmolarity alleviates contact-lens-induced edema..

Speaker: Professor, Department of Chemical and Biomolecular Engineering, Vice Chair, Undergraduate Affairs, University of California, Berkeley
Host: Kenneth Polse

Room 489