Sudden Acquired Retinal Degeneration Syndrome (SARDS) in Dogs
Dogs are highly resilient, adaptable creatures, but few disabilities affect dogs as profoundly as blindness. Sudden Acquired Retinal Degeneration Syndrome (SARDS) is a disease that causes rapid and complete blindness in dogs. It most frequently affects middle-aged dogs, but can strike dogs at any age. Little is known about the underlying cause of this disease, and there is currently no known treatment.
What is SARDS?
SARDS affects the thin visual cell layer of the retina that receives visual input and transfers it to the brain. Within this layer lies photoreceptors (or rods and cones), as well as the nerve fiber layers within the retina. Rapid degenerative changes occur in this layer, resulting in total blindness. According to studies conducted to understand the pathophysiology of SARDS, an unknown trigger sets off a biochemical cascade, causing apoptosis, which is the sudden and rapid cell death of rods and cones. Once the visual nerve cell layer of the retina is destroyed, it cannot regenerate.
Symptoms of SARDS
The first signs of SARDS often become apparent when the pet owner notices that their dog is stumbling and failing to track visual triggers. They may have difficulty maneuvering at night and bump into large items that they should otherwise be able to see. Since complete blindness can happen within days or weeks, a newly blind dog will appear confused and disoriented in their otherwise familiar environment. In the weeks or months prior to their blindness, dogs may experience dramatic increases in appetite and thirst, resulting in weight gain and increased urination.
A veterinary ophthalmologist examination may show a normal appearing retina, but the pupils are usually dilated and non-responsive or minimally responsive to light stimulation. The menace response test involves rapidly bringing a hand or other item toward the dog’s eyes, and should normally cause a dog to close his or her eyes. In a dog with SARDS, that response will fail, as will the ability to visually track moving items. An electroretinogram (ERG) may be recommended to assess retinal function. For this test, a special contact lens is placed in the dog’s eyes, followed by a series of lights being flashed into the eye. Electronic signals are recorded, and will be absent in a dog with SARDS. Routine blood and urine testing may suggest Cushing’s Syndrome. Although the connection between Cushing’s Syndrome and SARDS is unclear, dogs should be treated for their Cushing’s, despite the fact that it will not restore lost vision.
It is important for the veterinarian to first rule out other causes of acute blindness, such as optic neuritis, tumors invading the optic nerve, brain tumors, or other inflammatory conditions, because they could be treatable conditions that may restore vision or save the pet’s life.
Living With SARDS
Pets with SARDS are not experiencing pain and can resume a normal life, but they may be confused about their sudden blindness. Survey the dog’s environment, and remove any sharp items or things that may cause injury to the eyes. Consider any pools or stairs that could be hazards for a blind dog. Overall, dogs adjust to their blindness quite well, but information on training and living with blind dogs is widely available through a veterinarian or online.