Physiological changes in the cornea of the ageing eye.

Donor human corneas were studied in vitro for the viability of their endothelia. Endothelial ionic permeability (measured by electrical conductivity) and bicarbonate pump activity (measured by short circuit current) were recorded. Paired corneas were used to monitor post-mortem deterioration times and drug therapy immediately prior to death noted, when possible, to identify any possible effect on tissue performance. Donor age was correlated with some loss of endothelial pump capability. In adults it seems that pump capability deteriorates with a half time decay of 72 years (correlation coefficient, 0.69). Typically, between 60 and 90 years, endothelial pump capability may drop from 32 mu amps.cm-2 to 22 mu amps.cm-2, although at any particular age, the natural variation is +/- 6 mu amps.cm-2. Over the same period, endothelial permeability does not deteriorate and there is a suggestion that the endothelial cells may even tighten up with ageing, thereby partially compensating for the suggested ageing diminution in metabolic pump capability. There is no obvious age threshold for endothelial deterioration. The use of paired corneas revealed a 50 per cent loss in endothelial barrier function per 4.8 days of storage, and less than 5 per cent loss of pump capability over a similar period. The eyes were stored whole in a moist chamber at 0-4 degrees C. A significant group of donor eyes had a markedly reduced pump capability which was not age related. The patients had had terminal drug treatments which included digoxin and furosemide.