Corneal degenerations are among the most commonly observed clinical disorders in ophthalmology. They may be classified as (1) aging changes, (2) depositions, and (3) marginal degenerations. Aging changes are often incidental findings and do not usually interfere with vision. Depositions can occur secondary to previous ocular disease or trauma. Marginal degenerations are generally of unknown etiology, however, they may sometimes accompany a systemic disorder. The diseases in this latter group are usually the most difficult to treat and the most visually disabling.