Cryopreservation of rabbit and cat corneas at -18 to -24°C

A simple method of corneal cryopreservation, in which corneas were frozen at -18 to -24°C, was examined. Rabbit and cat corneas were placed successively in solutions of 50% fetal calf serum in McCarey-Kaufman medium with an increasing glycerol and glucose content. They were then frozen and stored in a -20°C domestic freezer. Rabbit corneas stored in this way were examined in vitro by light and scanning electron microscopy, and both rabbit and cat corneas were also assessed after orthotopic allotransplantation into adult recipient animals. Functional corneal grafts were obtained with rabbit and cat tissue that had been cryopreserved for 3-4 weeks and 1 week, respectively. Endpoint analysis (by light and scanning electron microscopy) of grafts that had survived for 50 days indicated the presence of an intact corneal endothelial monolayer. The corneal endothelium slowly degenerated as the storage time was increased. Importantly, however, the endothelium appeared to withstand the freezing and thawing processes and we conclude that it may be possible to store corneas at temperatures above -196°C, without the need for complex, low-temperature cryopreservation systems.