Disorders of the Retina

Laurie Anne Walden, DVM

Photo by kowal854 on flickr

The retina is a structure made of layers of photoreceptor cells and nerve cells at the back of the eye. The retina converts light into electrical signals that are sent to the brain to be interpreted as visual images.
 
Disorders of the retina cause vision loss. Whether the animal becomes completely and permanently blind depends on the cause. Inherited disorders, infection, inflammation, eye trauma, eye cancer, and metabolic diseases that affect the whole body can all cause retinal disorders.
 
Progressive Retinal Atrophy
Progressive retinal atrophy is the name for a group of inherited disorders that cause gradual blindness as the retina degenerates. Progressive retinal atrophy is most common in purebred dogs but also happens in cats and mixed-breed dogs. Some of the dog breeds at more risk than others are poodles, cocker spaniels, Labrador retrievers, golden retrievers, miniature schnauzers, dachshunds, Siberian huskies, mastiffs, and pugs.
 
Depending on the genetic variation, progressive retinal atrophy can cause vision loss starting very young (in puppies) or later in life. Vision gradually deteriorates over time. Affected animals eventually become blind.
 
Night blindness—loss of vision in low light—is the first sign in many animals. Because dogs and cats usually adapt well to vision loss, owners might not realize their pet’s vision has been affected unless they move the furniture or take their pet to an unfamiliar place. The condition isn’t painful and doesn’t affect the rest of the body, so animals with progressive retinal atrophy don’t feel unwell.
 
Progressive retinal atrophy is diagnosed with an eye examination, usually by a veterinary ophthalmologist. Electroretinography, which measures electrical activity in the retina, is also sometimes used. DNA tests can identify genetic variations that put a dog at risk.
 
No treatment for progressive retinal atrophy is available. However, because affected animals feel fine, they can continue to live normal lives with environmental management (to prevent falls from heights, for example). Some animals with progressive retinal atrophy also develop cataracts, but they aren’t good candidates for cataract surgery because they would still be blind after the surgery. Animals carrying genetic variations linked to progressive retinal atrophy shouldn’t be used for breeding.
 
Retinal Detachment
Retinal detachment is separation of layers of the retina from their normal position. The many possible causes include high blood pressure, eye trauma, infection, inflammation inside the eye, immune system problems, eye cancer, and inherited conditions of the retina.
 
Depending on the cause, retinal detachment can affect one or both eyes and can cause gradual vision loss or sudden total blindness. If the cause is something that affects the whole body, the animal might have other signs of illness.
 
Retinal detachment is diagnosed with an eye examination and sometimes ultrasonography of the eye. Other tests are needed to find the cause.
 
Treatment for retinal detachment depends on the cause and whether the retina is only detached or is also torn. Medical treatment is aimed at whatever caused the retinal detachment. In some cases, the retina can be repaired surgically. The best chance for saving vision is by diagnosing and treating the detachment very soon after it occurs.
 
Sudden Acquired Retinal Degeneration Syndrome
Sudden acquired retinal degeneration syndrome (SARDS) causes sudden total blindness in dogs because of loss of function of the photoreceptor cells of the retina. The cause is not known.
 
Dogs of any breed, including mixed-breed dogs, can be affected. Miniature schnauzers, dachshunds, pugs, and other small dogs seem to have SARDS more often than others, according to the American College of Veterinary Ophthalmologists. The average age of onset is 7 to 10 years.
 
Along with vision loss, many patients with SARDS have decreased energy and increased appetite, thirst, and urine volume during the first few months. These signs are similar to those of hyperadrenocorticism (Cushing disease). However, no definite link to endocrine disorders like Cushing disease has been found. Ongoing research has suggested that SARDS might be caused by a neuroendocrine or autoimmune disorder, but these possibilities also haven’t been proven.
 
SARDS is diagnosed by electroretinography showing no electrical activity in the retina. An eye examination won’t show any abnormalities at first. After some time has passed, a veterinary ophthalmologist might find retinal degeneration on examination.
 
Because we don’t know how or why SARDS develops, it’s not possible to predict which dogs are at risk. There is also no treatment. Dogs with SARDS become fully blind but still have a good quality of life with some help from their owners to keep them safe.
 
More Information
To read more about eye disorders in animals, see the American College of Veterinary Ophthalmologists website: https://www.acvo.org/common-conditions1.
 
Image source: https://www.flickr.com/photos/kowal854/49042126841/

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