Diseases of the retina include a wide spectrum of photoreceptor-affecting phenotypes that have been mapped to >120 loci on the human genome (RetNet Retinal Information Network). Currently, less than half of the causal genes have been identified (RetNet Retinal Information Network), although substantial progress has been made in determining the genetic basis of monogenic eye disorders. Mutations in new genes that are responsible for some form of retinal degeneration are identified on a regular basis. The vast majority of these genes are involved in rare phenotypes in a limited numbers of patients.