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Cryopreservation for corneal storage.

Currently, cryopreservation is the only method that offers the prospect of truly long-term storage of living cells and tissues. Despite some successful cryopreserved corneal grafts, freezing has been shown to damage the endothelium. When isolated cells are frozen, there are two principal mechanisms of damage: intracellular freezing, which occurs at high cooling rates, and solution effect injury at low cooling rates. When tissues are frozen, there are additional factors that appear to render cells more susceptible to intracellular freezing. Lower cooling rates appear to overcome this when freezing cornea. Vitrification is a way of achieving ice-free cryopreservation, but it also poses considerable challenges owing to the very high solute concentrations required to achieve vitrification at practicable cooling rates. Encouraging results have also been reported for cornea frozen using non-permeating cryoprotectants, which could lead to simpler methods of corneal cryopreservation.