Some effects of hydrostatic pressure on corneal hydration during specular microscopy

Abstract

Studies were made on the effects of hydrostatic pressure on the hydration of intact, de-epithelialized, de-endothelialized and denuded corneas mounted for specular microscopy and perfused with normal Ringer of perfused with bicarbonate and carbon dioxide-free Ringer which is claimed to “switch off” the endothelial pump. Rapid transient changes in thickness of any cornea are caused by rapid changes in hydrostatic pressure during an experiment such that, for example, an increase in hydrostatic pressure causes a decrease in corneal thickness before any subsequent effects are seen. Hydrostatic pressures below about 50 cm water have negligible effect (other than that of transient thickness change with rapid change in hydrostatic pressure) on the hydration of corneas with an intact epithelium whatever the condition of the endothelium, that is, in de-endothelialized preparations as well as in intact corneas with pumping or with non-pumping endothelia. If a cornea has no epithelium, hydrostatic pressure can balance the swelling pressure of the stroma to maintain a constant thickness in the absence of a pumping endothelium, that is, “equilibrium” thicknesses occur in denuded corneas (bare stroma), and in de-epithelialized corneas with endothelial pump “switched off”, which are related to the applied hydrostatic pressure. Hydrostatic pressure alone can act to deturgesce swollen de-epithelialized corneas whether the endothelial pump is “switched on” or is “switched off” or the endothelium removed. These findings are discussed in relation to corneas swollen considerably (>25%) above physiological thickness as often encountered in long-term refrigerated or cryopreserved preparations.