Contact lens wear can cause a number of physiological changes in the cornea. Two areas of interest in my laboratory have been contact lens effects on the endothelium and, more recently, the role of metabolic activity in predicting corneal swelling. The first part of this review focuses on the function of the corneal endothelium, the nature of its fluid pump, and the effects of contact lens-induced hypoxia and corneal pH changes on corneal endothelial function. In the second part, the etiology of hypoxia-induced corneal swelling is reviewed in relation to new studies on the causes of intersubject corneal swelling variability. The results indicate that corneal swelling is influenced by both corneal metabolic activity and endothelial function.