An analysis of the corneal endothelium of a 23 year old female who had never worn contact lenses but who had unilateral ptosis, showed marked endothelial pleomorphism of the cornea underneath the closed lid. Since corneal hypoxia has been shown to produce corneal endothelial polymegethism in contact lens wearers, and since hypoxic condtions exist under the closed lid, it is reasonable to assume that the polymegethous endothelial changes which occur with aging are a result of chronic corneal exposure to hypoxic conditions under the closed lid during sleep. Corneal hypoxia is apparently not the cause of declining endothelial cell density with age.