Some Aspects of Corneal Physiology in extended Contact Lens Wear

Abstract

Changes in the physiology of the human in vivo cornea during periods of contact lens wear are manifest in many different ways. The aim of the experimental work described in this thesis was to examine: (1) Apparent in vivo human corneal oxygen uptake rates. (2) Apparent corneal endothelial cell density. An existing apparatus for the measurement of in vivo corneal oxygen uptake rates was modified to improve the accuracy and repeatability of measurement. Using this apparatus the following aspects of human in vivo corneal oxygen consumption rates were observed: (a) A wide variation in individual oxygen consumption which conformed to a normal distribution. (b) A diurnal study which showed no change in oxygen uptake rate throughout the waking hours. (c) A change in oxygen uptake rate induced by changes in the fit of one form of soft contact lens. (d) A change in the oxygen demand of a non-contact lens wearing eye, induced by the wearing of a contact lens in the contralateral eye. (e) A reduction in oxygen consumption rate during a six month period of extended soft contact lens wear. An existing photo slit lamp technique for corneal endothelial photography was utilised together with a microfilm projection device to enable cell counts to be carried out. The instrumental variability of the system was determined and no change in apparent endothelial cell densities during a six month period of extended contact lens wear was observed. It is concluded that the wearing of an extended wear soft contact lens causes a change in apparent corneal oxygen uptake rate, but no change in endothelial cell density.