Retinal dysplasia and retinal folds

Written by Dr. Julie Gionfriddo, D.V.M., Dip. A.C.V.O. and edited by Dr. Hacker

Anatomy and Physiology

The retina is the structure inside 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 in the brain this is how we see. The development of the retina when we are in our mothers is quite complex. The eye develops from a small section of the front of what becomes the brain of the adult. Malformations of the retina before birth can occur and may be due to either hereditary, toxicity or virus infection.

Pathology

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 developmental layers of the retina do not unite properly. When this occurs, it is just like taking two different lengths of material and sewing them together. Folds or larger problems may develop.

Dysplasia may manifest as folds in the 'inner retinal layer'. These are called "retinal folds". In "geographic" retinal dysplasia there are larger areas of abnormal retinal development. In the most severe form of dysplasia, the 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 re-examination is recommended 6 months later 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 folds in the tapetal fundus of a puppy (arrows mark folds).

Retinal folds along the blood vessels of the retina (arrows mark some of the folds).

Affected Breeds

Retinal dysplasia is reported in 25 of the more than 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. In many breeds ophthalmologists and researchers have not determined exactly how retinal dysplasia is passed. In the Labrador retriever and Samoyed breeds, a combination of retinal dysplasia and skeletal defects (dwarfism) 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 (animals with two identical genes, one from the mother and one from the father) have skeletal changes and mild-to-severe retinal dysplasia while heterozygous animals (different genes one from the mother and one from the father, only one of which is abnormal) usually have just mild retinal dysplasia.

Retinal folds rarely cause vision problems for the individual dog. They represent small blind spots which are 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 whether dogs with retinal folds will "pass" a CERF examination. Retinal folds may be seen in certain breeds and still pass a CERF examination and receive a CERF number. This is due to the fact that the condition is thought to either not 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.

Key:
Colour	Breeding Advice
	NO
	Breeder's Option
	Unknown

Breeds Affected With Retinal Dysplasia
Breed	Folds	Geographic	Detachment	Comments
Airedale		.	.	.
American Water Spaniel		.	.	.
Australian Cattle Dog		.	.	.
Australian Kelpi		.	.	.
Australian Shepherd		.	.	.
Basset Griffon Vendeen, Petite			.	.
Bearded Collie		.	.	.
Bedlington Terrier				.
Bulldog		.	.	.
Bullmastiff		.	.	.
Cavalier King Charles Spaniel				.
Chesapeake Bay Retreiver			.	.
Cocker Spaniel - American				.
Cocker Spaniel - English		.	.	.
Collie		.	.	.
English Springer Spaniel				.
English Toy Spaniel		.	.	.
Field Spaniel			.	.
German Shepherd			.	.
Giant Schnauzer		.	.	.
Golden Retreiver		.	.	.
Labrador Retreiver				May or may not be oculoskeletal dysplasia
Mastiff		.	.	.
Puli		.	.	.
Rottweiler		.	.	.
Samoyed				May or may not be oculoskeletal dysplasia
Sealyham Terrier				.
Shiba Inu		.	.	.
Standard Schnauzer		.	.	.
Sussex Spaniel		.	.	.
Tibetan Terrier			.	.
Welsh Corgi, Cardigan		.	.	.
Welsh Corgi, Pembroke			.	.

Have any questions on this subject? Contact Dennis Hacker via E-mail:

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