The retina is a thin, delicate membrane that lines the backs of the eyes. It is supported and nourished by the choroid, a layer of pigmented vascular tissue behind the retina.
In dogs, the retina has a layer of reflective cells behind it called the tapetum lucidum. This layer reflects light back to the front of the eye – causing the glowing eyes in photos of dogs. This reflective layer helps dogs see better in poor light, because the retina gets two chances to absorb the light. In dogs with retinal diseases, the retina loses some or all of its capacity to perceive light. The majority of retinal diseases in dogs are inherited and are transmitted when an affected or carrier dog is used for breeding. Therefore, to control the prevalence of retinal disease, it is important to determine before a dog is used for breeding whether that dog is affected. Inherited eye disease can often be identified at an early age by a routine eye examination performed by a veterinary ophthalmologist, most of whom are affiliated with the Canine Eye Registry Foundation (CERF).
CERF was established in 1974 with two purposes:
- To screen purebred dogs for inherited eye diseases and issue certificates to those free of disease.
- To collect research data on the incidence of various inherited eye diseases.
In 1989, the activities of CERF were combined with those of the Veterinary Medicine Data Bank at Purdue University. More recently, the Canine DNA Registry has been added to the Data Bank.
Dogs are screened for all types of hereditary eye diseases during a CERF examination. There are more than 260 board-certified veterinary ophthalmologists affiliated with CERF throughout the United States and Canada. A dog receives a certification based on the appearance of the eyes at the time of the examination. Because some inherited eye diseases develop later in life, certification is good for only one year and must be repeated annually. Furthermore, certification does not imply clearance for the carrier state. Dogs who are unaffected by disease may or may not be carriers of the gene that causes that disease.
CERF maintains a website that contains the names of all dogs who have a current CERF certification. The site is updated at the beginning of each month. The American Kennel Club now incorporates CERF certification on pedigrees. This will only tell you which dogs were checked and found to be normal, but it is important information. OFA now has access to CERF records as well. Your veterinarian can refer you to a veterinary ophthalmologist affiliated with CERF in your area, or you can contact CERF directly.
Because the CERF registry is closed (that is, the identity of affected dogs remains confidential), CERF information cannot be used to determine which ancestors in a dog’s pedigree may have been affected. The Institute for Genetic Disease Control in Animals (GDC) also maintains a registry for hereditary eye diseases. This open registry allows breeders to share the results of eye examinations on all dogs registered with the GDC, including those who are found to be affected by genetic eye diseases. Knowing which ancestors are affected makes it possible to determine which progeny may be carriers. This knowledge can be of value in selecting breeding animals who are at low risk for transmitting the disease.