The retina is the neurological structure in the back of the eye which receives light and converts it into an electrical signal. This electrical signal is transmitted to the brain by way of the optic nerve and is interpreted by the brain as vision. The embryological development of the retina is quite complex. It forms from a small part of the front of the primitive neural tube, the structure that becomes the nervous system (brain and spinal cord) of the adult. Malformations of the retina before birth are rare but can be due to either hereditary or environmental (in the uterus) influences. Retinal dysplasia is a type of retinal malformation. The word "dysplasia" simply means "a defective development of an organ or structure". Retinal dysplasia occurs when the 2 primitive layers of the retina do not form together properly. Mild dysplasia manifests as folds in the inner retinal layer. These are called "retinal folds". In "geographic" retinal dysplasia there are larger areas of defective retinal development. In the severe form of dysplasia, the 2 retinal layers do not come together at all and retinal detachment occurs. Retinal dysplasia is not progressive. It is a congenital defect and animals are born with as severe a condition as they will ever get. Retinal dysplasia can be detected as early as 6-8 weeks on a CERF examination. However, because the size of the eye is small and young puppies are often wiggling during examination, a 6 month recheck is recommended in order for the ophthalmologist to better see the back of the eye.
The cause of retinal dysplasia in most breeds is genetic although prenatal infections with herpesvirus and parvovirus may also lead to it. Retinal dysplasia is reported in 25 of the 100 breeds of dogs listed in the 1996 edition of the CERF book Ocular Disorders Presumed to be Hereditary in Purebred Dogs. Twenty-four of these breeds had retinal folds reported, and 11 had geographic areas of dysplasia and/or retinal detachment. Simple autosomal recessive inheritance has been suspected in Akitas, American Cocker Spaniels, Australian Shepherds, Bedlington Terriers, Beagles, Dobermans, English Springer Spaniels, Labradors, Rottweilers, Old English Sheepdogs, Sealyham Terriers, and Yorkshire Terriers. The means of inheritance has not been determined in many breeds. In Labradors and Samoyeds a combination of retinal dysplasia and skeletal defects has been described. This condition is known as oculoskeletal dysplasia. In this condition an autosomal dominant gene is thought to be responsible for the genetic defects. Homozygous animals have skeletal changes and mild to severe retinal dysplasia while heterozygous animals usually have mild retinal dysplasia.
Retinal folds rarely cause vision problems for the individual dog. They represent small blind spots which are probably not even noticed by the dog. However, large areas of dysplasia (geographic dysplasia) may lead to large deficits in the visual field and dogs with retinal detachments are completely blind.
There have been many questions recently about the certifiability of
dogs with retinal folds. Retinal folds may be seen in many breeds
and still pass a CERF examination and receive a CERF number. This
is due to the fact that the condition is thought either not to be
hereditary in the particular breed or has never been shown
to be connected to serious (blinding) forms of dysplasia. In some
breeds, particularly Labrador Retrievers, Samoyeds, and English
Springer Spaniels, individuals with retinal folds are NOT given a
CERF number. Since retinal dysplasia is common in these breeds
and dogs and bitches with retinal folds can have puppies with
blindness and/or skeletal problems the gene should not be perpetuated.
In all breeds, individuals with geographic and retinal detachment
forms of retinal dysplasia are NOT certifiable.