Morphological study of cryopreserved human corneal endothelium

The aim of the present paper is to describe the morphological changes that occur in human corneal endothelium as an immediate consequence of corneal c ryopreservation. Therefore, 16 human donor corneas were cryopreserved with an original procedure at a 1 degrees C/min cooling rate in a freezing solut ion cryoprotected with 7% dimethylsulphoxide until a final temperature of - 100 degrees C was reached. After storage of the corneas in liquid nitro gen for periods ranging from 1 to 96 days (mean: 34.31 days), the corneas were thawed in a water bath at +37 degrees C. Eight additional control corneas were processed without cryopreservation. Morphological assessment of the en dothelial layer was performed by scanning electron microscopy and trypan bl ue and alizarin red S vital staining. Results showed cryoinduced damage at variable degrees in all cryopreserved corneas. They were classified into th ree groups according to the intensity and extension of the cryoinduced dama ge: group I (n = 10): corneas with minor endothelial alterations consisting in the presence of microholes in the posterior cell membrane; group II (n = 1): corneas with generalized disruption of endothelial intercellular junc tions and intact cell membranes; group III (n = 5): corneas with severe end othelial damage consisting of massive cell necrosis and complete alteration of the morphological pattern of the endothelium. All control corneas had i ntact endothelial layers. Cryoinduced damage cannot be completely avoided w ith the cryopreservation protocol tested. The high interindividual variabil ity of the results observed is not related to the storage time of the corne a in liquid nitrogen.