Eye discoloration can sometimes be a symptom of certain diseases and medical conditions. Primary acquired melanosis, for example, is a medical condition that most often affects middle-age or elderly caucasians, resulting in a brown patchy appearance to the sclera of the eye. While primary acquired melanosis does not generally affect the health or functioning of the eye, it must be monitored. According to researchers at the University of Utah John A. Moran Eye Center, certain forms of primary acquired melanosis can progress to melanoma, a very deadly form of skin cancer. Other diseases and medical conditions that can cause eye discoloration include Addison's disease, macular degeneration, and pigmentary glaucoma.