HUMAN CORNEAL ENDOTHELIAL TOLERANCE TO GLYCEROL, DIMETHYLSULFOXIDE, 1,2-PROPANEDIOL, AND 2,3-BUTANEDIOL

We exposed human corneas to various concentrations of four cryoprotect ants by one of two methods: a gradual increase to the final concentrat ion (ramp method) and a series of steps to the final concentration (st ep method). Endothelial damage was manifest as a decrease in the numbe r of endothelial cells per unit area. The highest concentrations that did not cause a loss of endothelial cells by the ramp and step methods , respectively, were 4.3 and 2.0 M glycerol, 2.0 and 4.3 M dimethylsul foxide, 2.0 and 3.0 M 1,2-propanediol, and 2.0 and 2.5 M 2,3-butanedio l. The ramp method achieved higher final concentrations with the more slowly permeating glycerol, but required low toxicity. The step method achieved higher final concentrations with the more toxic cryoprotecta nts by limiting the exposure time, but required more rapid permeation. None of the four cryoprotectants was tolerated at concentrations suff icient for vitrification at practical cooling and warming rates. (C) 1 994 Academic Press, Inc.