What is sudden acquired retinal degeneration syndrome?
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 days to weeks, 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 SARDS?
SARDS is idiopathic, meaning that the cause is unknown, though many 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. Work has also been done to find if this condition is neuroendocrine (hormonal) in nature, but the results are inconclusive.
The blindness associated with SARDS is due to the 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). The result is the entire retina degenerates over time, leading to blindness. SARDS is most often observed in middle-aged dogs, with an average age at onset of 8–10 years.
"Females are more likely to be affected by SARDS than males."
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, Shih Tzus, Beagles, and Maltese are also overrepresented.
What are the clinical signs of SARDS?
Dogs with SARDS appear to go blind very quickly. Some owners report periods where their dog still appears to have some small degree of vision, but most dogs seem to be completely blind. Affected dogs may bump into walls or furniture. They may appear disoriented, pacing aimlessly, or standing in one place for prolonged periods. Many dogs show reluctance to be separated from their owner. Affected dogs are also often reluctant to go up or down steps. Their overall activity level may decrease, as they avoid moving around their environment. The pupils 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."
In some cases, dogs with SARDS have a history of clinical signs consistent with Cushing’s disease. These signs include increased thirst, urination, and appetite, excessive panting, weight gain or obesity, and lethargy. It is unknown whether Cushing’s contributes to SARDS or whether this association is coincidental. There may also be an association between SARDS and liver disease, though this is also unconfirmed.
How is SARDS diagnosed?
SARDS is typically diagnosed with a thorough ophthalmologic exam. Your veterinarian will perform tests to assess your dog’s vision and visual reflexes. The pupils will not respond normally to light and your dog will show other responses consistent with blindness. In some cases, changes in the interior of the eye supporting a SARDS diagnosis may be visible, including 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). 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, 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 based on patient history and clinical signs observed in the veterinary exam.
"While there are typically no blood work changes seen with SARDS, these tests can help rule out other conditions that may cause blindness."
Your veterinarian may perform blood tests, including a complete blood cell count and serum biochemistries. While there are typically no blood work changes seen with SARDS, these tests can help rule out other conditions that may cause blindness. Given the correlation with Cushing’s disease, your veterinarian may 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).
What is the treatment and prognosis for SARDS?
Unfortunately, there is no treatment for SARDS. The blindness associated with this condition is permanent. A variety of treatments and supplements have been recommended and marketed for this condition, but there is no evidence that any of them are beneficial to affected dogs. If your dog is diagnosed with Cushing’s disease during the workup for SARDS, Cushing’s disease can be treated with a variety of medications. Treating this disease, however, will not restore your dog’s vision.
Most dogs will adjust to their blindness within a few weeks. During this adjustment period, your dog may need additional supportive care. Avoid moving furniture or other large items within your home to allow your dog to learn to navigate her surroundings. When let outside, your dog should be walked on a leash or confined to a fenced area so that she does not wander off and become injured.
Owners sometimes worry about whether the behavioral changes that accompany blindness will be permanent and 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.
