The etiology of transient endothelial changes in the human cornea

To investigate the etiology of contact lens-induced transient endothelial changes (blebs) in the human cornea, the effects of five different stimuli on corneal thickness and the appearance of the corneal endothelium were assessed. The stimuli included: (1) a silicone contact lens; (2) a silicone contact lens in combination with anoxia; (3) anoxia alone; (4) a thick hydroxyethyl methacrylate (HEMA) contact lens; and (5) a gas mixture of 9.8% carbon dioxide, 20.5% oxygen, and the balance nitrogen. The silicone lens alone produced no significant alteration in endothelial appearance and little change in corneal thickness. However, when nitrogen gas was passed in front of the lens, a typical bleb response was observed. This indicates that the physical presence of a contact lens is insufficient by itself to produce transient endothelial changes. Anoxia alone induced corneal swelling and endothelial bleb formation, indicating a metabolic component in the bleb response. The gas mixture containing 9.8% carbon dioxide also altered the endothelial appearance but had no significant effect on corneal thickness. The thick HEMA lens produced changes in both the appearance of the endothelium and corneal thickness. The only factor common to the stimuli which induced blebs would appear to be their ability to change the pH in or near the corneal endothelial layer.