What is sudden acquired retinal degeneration?
Sudden acquired retinal degeneration syndrome (SARDS), is a condition that causes rapid and irreversible blindness due to changes within the retina. This condition develops over a period of 30 days or less, though some cases may come on more gradually. In many cases, the blindness associated with SARDS seems to come on almost overnight, as animals suddenly reach the point where they can no longer compensate for their decreased vision.
What causes sudden acquired retinal degeneration?
SARDS is idiopathic, meaning that we do not know what causes it. Multiple theories have been considered. Some speculate that SARDS may be caused by autoimmune inflammation within the retina, but there is no proof of this theory.
The blindness associated with SARDS is due to abnormal function of multiple receptor types within the retina (receptors are specialized cells that convert light into electrical signals that are sent to the brain via the optic nerves). It is unknown, however, whether the abnormality occurs in the receptors themselves, or in the nerves that transmit the signals to the brain
SARDS is most commonly observed in middle-aged dogs, with an average age at onset of 8–10 years old. Females are more likely to be affected by SARDS than males. The condition is most common in mixed-breed dogs, though Dachshunds, Miniature Schnauzers, Pugs, Brittany Spaniels, Bichons, Cocker Spaniels, Springer Spaniels, Beagles, and Maltese are also overrepresented.
What are the signs of SARDS?
Dogs with SARDS appear to go blind very quickly, over a period of days to weeks. Some owners report periods of time where their dog still appears to have some small degree of vision, but most dogs seem to be completely blind.
Affected dogs are often seen bumping into walls or furniture. They may appear disoriented, pacing aimlessly, or standing in one place for prolonged periods of time. Many dogs show reluctance to be separated from their owner. Affected dogs are also often reluctant to go up or down stairs. Their overall activity level may decrease, as they avoid moving around their environment. The pupils (dark portion of the eye) often remain dilated, instead of constricting (narrowing) in response to light as they normally would. Some owners also notice a decrease in hearing or smell around the time that vision is lost.
In some cases, dogs with SARDS have a history of clinical signs consistent with Cushing’s disease. These signs include increased thirst, increased urination, increased appetite, excessive panting, weight gain or obesity, and lethargy. It is unknown whether Cushing’s contributes to SARDS or whether this association is only coincidental. There may also be an association between SARDS and liver disease, though this association is also unconfirmed and not fully understood.
How is SARDS diagnosed?
SARDS is typically diagnosed on the basis of a thorough ophthalmologic exam. Your veterinarian will perform a number of tests to assess your dog’s vision and visual reflexes. The pupils will not respond normally to light and your dog will show a number of other responses consistent with blindness.
In some cases, changes may be visible on examination of the interior of the eye that can support SARDS. These changes include changes to the blood vessels and increased reflectivity within the eye (as the retina thins, reflection from a structure behind the retina called the tapetum lucidum is more intense). These changes are diagnostic for SARDS but it is important to keep in mind that these changes are not always apparent (especially early in the course of the disease).
The only way to definitively diagnose SARDS is with a test called electroretinography (ERG). This test involves flashing a bright light in front of the eye and monitoring the electrical activity of the retina. If there is no electrical activity within the retina (a ’flat line’), the dog can be definitively diagnosed with SARDS. However, this test is rarely performed because it requires referral to a veterinary ophthalmologist. Therefore, most cases of SARDS are diagnosed on the basis of history and clinical signs on veterinary exam.
"Most cases of SARDS are diagnosed on the basis of history and clinical signs on veterinary exam."
Your veterinarian may perform blood tests, including a complete blood cell count and serum biochemistries. While there are typically no bloodwork changes seen with SARDS, this bloodwork can help rule out other conditions that may cause blindness. Given the correlation between SARDS and Cushing’s disease, your veterinarian may also recommend a test for Cushing’s disease. There are two separate tests available for this condition: an ACTH stimulation test and a low-dose dexamethasone suppression test (see handouts “Cushing's Disease in Dogs” and Cushing’s Disease – Testing” for more information on this disease and testing).
What is the treatment and prognosis for SARDS?
Unfortunately, there is no treatment for SARDS. The blindness associated with this condition is permanent and irreversible. A variety of treatments and supplements have been recommended and marketed for this condition, but there is no evidence that any of these treatments offer benefits to affected dogs.
If a dog is noted to have Cushing’s disease during its workup for SARDS, Cushing’s disease can be treated with a variety of medications. Treating Cushing’s disease, however, will not help restore the dog’s vision.
"Most dogs will adjust to their blindness over a period of 6-8 weeks."
Although SARDS can initially be stressful and concerning, most dogs will adjust to their blindness over a period of 6 to 8 weeks. During this adjustment period, your dog may need additional supportive care. Avoid moving your furniture or other large items within your home, in order to give your dog an opportunity to learn to navigate his surroundings. When let outside, your dog should be walked on a leash or confined to a small, fenced area, so that he does not wander off and become injured.
Owners sometimes worry about whether the behavioral changes that accompany blindness will be permanent. However, they are typically pleasantly surprised to find that this is not the case. Once dogs have had time to adjust to their loss of vision, over 75% of dog owners rate their dog’s quality of life as excellent.