Sudden Acquired Retinal Degeneration Syndrome (SARDS)

What is sudden acquired retinal degeneration syndrome?

Sudden acquired retinal degeneration syndrome (SARDS) is a condition that causes rapid and irreversible blindness due to degeneration of the retina, the light-sensitive tissue lining the back of the eye.

This condition typically develops over days to weeks, although it may progress more gradually in some cases. In many dogs, blindness associated with SARDS appears to occur almost overnight, as they suddenly reach the point where they can no longer compensate for their declining vision.

What causes SARDS?

SARDS is idiopathic, meaning that its cause is unknown, although 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. Researchers have also investigated whether 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. These receptors are specialized cells that convert light into electrical signals, which are sent to the brain through the optic nerves. As these receptors stop functioning normally, the retina gradually degenerates, leading to blindness. SARDS is most often observed in middle-aged dogs, with an average age at onset of 8 to 10 years.

Female dogs are more likely to be affected by SARDS than male dogs. The condition is most common in mixed-breed dogs, although several breeds are overrepresented, including Dachshunds, Miniature Schnauzers, Pugs, Brittany Spaniels, Bichons, Pomeranians, Cocker Spaniels, Springer Spaniels, Shih Tzus, Beagles, and Maltese.

What are the signs of SARDS?

Dogs with SARDS appear to go blind very quickly. Some owners report periods during which their dog still appears to have a small degree of vision, but most dogs appear completely blind. Affected dogs may bump into walls or furniture. They may appear disoriented, pace aimlessly, or stand in one place for prolonged periods. Many dogs show reluctance to be separated from their owners.

Affected dogs are often reluctant to go up or down stairs. Their activity level may decrease as they avoid moving around their environment. The pupils often remain dilated instead of constricting (narrowing) in response to light. Some owners also notice a decrease in hearing or smell around the time that vision is lost.

Some dogs with SARDS have a history of clinical signs associated with Cushing’s disease, including:

• Increased thirst
• Increased urination
• Increased appetite
• Excessive panting
• Weight gain or obesity
• Lethargy

It is unknown whether Cushing’s disease contributes to SARDS or whether this association is coincidental. There may also be an association between SARDS and liver disease, although this has not been confirmed.

How is SARDS diagnosed?

SARDS is typically diagnosed after a thorough eye examination. Your veterinarian will 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 within the eye that support a diagnosis of SARDS may be visible, including changes to the blood vessels and increased reflectivity within the eye. Increased reflectivity occurs because the retina becomes thinner, making the tapetum lucidum (a reflective structure located behind the retina) easier to see. It is important to keep in mind that these changes are not always present, especially early in the course of the disease.

The only way to definitively diagnose SARDS is with a test called electroretinography (ERG). During this test, a bright light is flashed in front of the eye while the electrical activity of the retina is measured. If no retinal electrical activity is detected, a diagnosis of SARDS can be confirmed. However, this test is not commonly performed because it typically requires referral to a veterinary ophthalmologist. For that reason, most cases of SARDS are diagnosed based on the patient’s history, clinical signs, and examination findings.

Your veterinarian may perform blood tests, including a complete blood cell count and serum biochemistry profile. Although SARDS does not typically cause changes in routine bloodwork, these tests can help rule out other conditions that may contribute to blindness. Given the association between SARDS and Cushing's disease, your veterinarian may also recommend testing for Cushing’s disease. Two commonly used tests are the ACTH stimulation test and the low-dose dexamethasone suppression test.

What is the treatment and prognosis for SARDS?

Unfortunately, there is no treatment for SARDS, and 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 improve vision or slow disease progression. If your dog is diagnosed with Cushing’s disease during the SARDS workup, it can often be managed with medication. However, treating Cushing's disease will not restore your dog’s vision.

Most dogs adjust to their blindness within a few weeks. During this adjustment period, your dog may need additional support:

• Keep your dog's environment as consistent as possible.
• Avoid moving furniture and other large objects around your home so your dog can learn to navigate the environment.
• When outside, keep your dog on a leash or within a securely fenced area so that they do not wander off and become injured. 
• Take extra care around stairs and other hazards. 
• Avoid having your dog’s whiskers clipped during grooming, as they may help your dog navigate the environment.

Owners often worry that the behavioral changes associated with blindness will be permanent. Fortunately, this is usually not the case. Once dogs have had time to adjust to vision loss, more than 75% of dog owners rate their dog’s quality of life as excellent.