Dog Retinal Detachment
The retina is a delicate, thin, multi-layered membrane that lines the back of the eyes. The retina contains cells known as rods and cones, which are essential to sight. Retinal detachment is defined as separation of the inner layers of the retina (called the neural retina) from its underlying pigmented layers (called the retinal pigment epithelium, or RPE). The extent of retinal detachment will determine the degree and severity of vision impairment in any particular animal.
Causes of Retinal Detachment
Retinal detachment can be caused by several things. It can be a primary hereditary disorder, which usually is inherited through autosomal recessive genetic expression, but sometimes is inherited through incomplete dominant inheritance. The genetics of inheritance of this condition are beyond the scope of this article. Retinal detachment can also be secondary to an acquired intraocular (inside of the eye) abnormality. In dogs, severe retinal detachment is often congenital, which means that it is present at birth. Collies can develop a condition called collie eye anomaly, in which retinal detachment is present in up to 10% of affected animals. Older dogs can develop acquired retinal detachment as a result of systemic high blood pressure (hypertension) or other age-related conditions that develop over time. Acquired detached retinas can also be associated with trauma to the eyes, inflammation, infection, glaucoma, cataracts, cancer/tumors, intraocular bleeding disorders, ocular (eye) surgery and simply old age.
Hereditary retinal detachment can best be prevented by not breeding affected animals or animals that are carriers of the abnormal gene. Veterinary eye specialists can screen dogs that owners are considering using for breeding and can register the results of that screening through the Canine Eye Registration Foundation (CERF). This process can help responsible, reputable breeders to remove dogs with hereditary forms of retinal detachment from the purebred breeding population.
Irreversible retinal degeneration can happen quickly after retinal detachment. This makes prompt diagnosis and treatment by a veterinary eye specialist extremely important in dogs with impaired vision.
How Retinal Detachment Affects Dogs
Retinal detachment can occur in one or both eyes – in other words, it can be unilateral or bilateral. It can also occur in only a small area of the affected retina (focal detachment), in multiple but separate areas of the retina (multifocal detachment) or across the entire affected retina (complete or total detachment). Focal retinal detachments that affect only small areas usually will not cause clinically detectable vision impairment. On the other hand, total detachment of the entire retina almost always causes blindness in the affected eye.
Symptoms of Retinal Detachment
The symptoms of retinal detachment are very similar to those of another disorder called retinal degeneration. These symptoms can include one or more of the following, in either or both of a dog's eyes:
Acute onset of blindness
Progressive vision loss
Night blindness or impaired night vision (nyctalopia)
Impaired day vision (hemeralopia)
Greenish, shiny reflection of the eyes (tapetal reflection in dilated pupils)
Dilated (enlarged) pupils
Asymmetrical pupil size (anisocoria)
Ocular discharge (+/- pus)
Bleeding (hemorrhage) inside the eyes
Dogs at Increased Risk
Retinal detachment is reported in many domestic dog breeds. It is presumed to be inherited as a recessive genetic trait in many breeds, including the American Cocker Spaniel, Bedlington Terrier, English Springer Spaniel and Miniature Schnauzer. Labrador Retrievers and Samoyeds can develop retinal detachment along with associated skeletal deformities because of what is thought to be incomplete dominant inheritance. Australian Shepherds, Border Collies, Collies and Shetland Sheepdogs are predisposed to retinal detachment in association with collie eye anomaly. Shih Tzus may also be at increased risk of retinal detachment.
How Retinal Detachment is Diagnosed
Retinal detachment is usually diagnosed when a dog's owner notices that her pet is having vision problems, and then brings the dog to its veterinarian for an evaluation.
A dog's treating veterinarian will perform a physical examination and take a complete history from the owner of a dog presenting with what appears to be vision impairment. If the condition merits further diagnostics, most general practitioners will refer the owner to a skilled veterinary eye specialist (ophthalmologist) for a thorough ophthalmic examination, which is extremely important when a dog develops obvious vision deficiencies, whether they come on slowly (are chronic) or suddenly (are acute). Veterinary ophthalmologists have many diagnostic instruments and tests at their disposal to localize the cause of the dog's disorder. These may include ocular ultrasound and microscopic evaluation of biopsy eye tissue samples, if the eye needs to be removed (enucleated) due to blindness and pain resulting from retinal detachment.
The signs of retinal detachment often mimic the signs of retinal degeneration. Although these are completely separate disorders, the symptoms are basically the same, and owners of affected dogs will essentially notice vision deficiencies in their pets.
The goals of treating dogs with detached retinas, from whatever cause, are to resolve the underlying cause of the condition and to restore vision (or preserve remaining vision) to the greatest extent possible.
A dog with acute onset of vision loss of unknown cause should be seen by a board certified veterinary ophthalmologist as soon as possible. Medical and/or surgical options may be available at very early times after the condition becomes evident, but they may no longer be available once the condition becomes chronic. Oral and topical medications, as well as those injected directly into the eye, may be helpful in some cases. Surgical treatments are highly specialized and require the input of a veterinary eye specialist. If the underlying cause is a potentially treatable systemic disorder, such as hypertension, retinal detachment may be reversible with medical management. But even if it is not, most dogs adjust very well to unilateral - and even to bilateral – vision loss.
The prognosis for dogs with detached retinas is highly variable. It depends upon the underlying cause of the condition and its duration, severity and the extent of damage to the dog's eyes. A dog with localized (focal) retinal detachment – especially if it is present in only one eye – typically has a good prognosis, particularly if the underlying cause can be identified, addressed and prevented from recurring. Unfortunately, dogs with complete detachment of the retina are unlikely to have vision return to the affected eyes.