Dogs bred to develop progressive rod cone degeneration will be studied using electroretinography and electronmicroscopy to determine the normal functional and structural development of the rod and cone photoreceptor system. In addition, the dogs will be used to investigate the temporal relation between the onset of rod and cone dysfunction. Autoradiographic studies of outer segment renewal will determine the relationship between degeneration and defects in the renewal system. This study will determine if the rod and cone degenerative processes occur concurrently and the structural basis for the functional deficit. BIBLIOGRAPHIC REFERENCES: Buyukmihci, N. and Aguirre, G.D.: Rod Disc Turnover in the Dog. Invest. Ophth., 15, 1976: 579-584. Aguirre, G.: Inherited Retinal Degenerations in the Dog. Trans. Am. Acad.Opth. & Otol., 81, 1976:OP-667-676.