A new preservation solution for storage of corneas at low temperatures.

Cryopreservation methods are only rarely used today for storing donor material for use in penetrating keratoplasty. There remains, however, a continuing need for a reliable technique for the long-term preservation of corneas. As a first step in developing an improved method of corneal cryopreservation we have studied the composition of the preservation medium. On the basis of experiments with other tissues a new solution (designated CPTES) has been formulated, containing concentrations of potassium, sodium and chloride similar to normal intracellular levels, in order to restrict the ionic imbalances that occur when temperature is reduced and ionic pumps switched off. An impermeant anion was included to reduce cellular swelling during low temperature storage. Integrity of the corneal endothelium was demonstrated following exposure to CPTES medium at 0 degree C: control of corneal hydration and the presence of an active bicarbonate - dependent pump were demonstrated by specular microscopy; normal ultrastructure of the endothelial layer was revealed by electron microscopy. The incorporation and removal of 1M dimethyl sulphoxide (Me2SO) is tolerated in corneas bathed in CPTES medium at 0 degree C, again with retention of endothelial structural and functional integrity. CPTES is proposed as a medium which will help to control osmotic and ionic disturbances during experimental procedures designed to improve methods of corneal preservation both above and below 0 degree C.