Canine progressive rod-cone degeneration (prcd) is a retinal disease previously mapped to a broad, gene-rich centromeric region of canine chromosome 9. An allelic disorders present in multiple breeds, and crosses of those breeds. Research strongly suggests that a common ancestor transmitted the prcd disease allele to many of the modern dog breeds. Diagnosis of prcd is based on a combination of clinical examination, including indirect ophthalmoscopy and electroretinography, and retinal morphology. Retinal photoreceptor abnormalities are visible in animals 14 weeks of age and older using high-resolution optical microscopy.