Heritable lens luxation, if not treated promptly, will induce secondary glaucoma. In addition, heritable primary glaucoma can cause secondary lens luxation. Since it is not always known whether lens luxation or glaucoma is the primary disease, we believe it is rational to study both diseases together. One or the other of these diseases is responsible for loss of sight in the Basset Hound, Border Collie, Dandie Dinmont Terrier, Jack Russell Terrier, Miniature Bull Terrier, Petit Basset Griffon Vendeen, Sealyham Terrier, Tibetan Terrier, Welsh Springer Spaniel, and Welsh Terrier. We are attempting to produce DNA marker assays that will identify dogs with the mutant gene responsible for lens luxation and glaucoma. Early identification of these dogs would enable dog owners and their veterinarians to instigate measures to preserve their dogs sight and to adjust breeding practices to minimize or eradicate the disease in their breeds.