ULTRASTRUCTURE OF CRYOPRESERVED, FUNCTIONING HUMAN CORNEAL ENDOTHELIUM

The endothelium was studied by light‐ and electronmicroscropy in a cryo‐preserved cornea transplanted to a woman with herpetic keratitis and removed after 18 months because of wound dehiscence and epithelialization of the anterior chamber. The graft was perfectly transparent and of normal thickness. Light microscopy revealed the existence of a continuous layer of endothelial cells, showing pronounced pleomorphism when examined in flat preparation, with large multinuclear cells between smaller more normal looking mononuclear cells. The heterogeneous cell pattern resembled that observable in vitro after freezing and 24 h of culture. The cells therefore are not considered to be in a steady state. The ultrastructure of the majority of the cells was similar to that of non‐cryopreserved endothelium. Cell cohesion took place by tight junctions, the intercellular spaces were of normal width. Ultrastructurally there was, however, a cellular heterogeneity, due to the occurrence of light cells with few organelles, but always with intact cell membranes. These cells probably represent slow death of endothelial cells, demonstrated by falling cell density during the 18 months between grafting and examination. We conclude from this study that cells surviving the freezing can maintain a clinically normal endothelial function for 18 months by forming a continuous quasistatic monolayer of tightly bound living cells.