Diagnosing Sudden Blindness in Dogs Can Be Confusing
Sudden acquired retinal degeneration syndrome (SARDS) is a baffling disease. It’s most dramatic symptom is the sudden onset of blindness, which sometimes seems to develop over the course of just a day or so. However, when a veterinarian performs an ophthalmological exam, the dog’s eyes appear perfectly normal. SARDS tends to affect dogs in middle age. Females, dachshunds, miniature schnauzers, and mutts are at higher than average risk.
What makes SARDS so bewildering is the fact that in many cases the disease doesn’t seem to affect only the eyes. Up to about 40 percent of dogs have systemic signs as well, many of which are often seen with Cushing’s disease (e.g., increased thirst, urination, and appetite). In these cases, the results of a standard panel of lab work also look similar to dogs with Cushing’s.
High liver values, a high alkaline phosphatase level, abnormally large amounts of cholesterol in the blood, a pattern of white blood cell abnormalities called a “stress leukogram,” urine that is dilute and contains higher than normal levels of protein, and high blood pressure may be observed. Despite all this, Cushing’s disease is only definitively diagnosed in a minority of dogs who have SARDS.
The truth is that we simply don’t know what causes SARDS in dogs. Some studies have supported the notion that it is an immune-mediated disorder, others have not. In many cases, the photoreceptors (both rods and cones) in the eyes of affected dogs appear to have undergone apoptosis (cell death) with little evidence of inflammation, but one study showed that problems with the nerve fibers within the eyes, not with the photoreceptors, appeared to be to blame for the dogs’ blindness.
These types of confusing and contradictory findings make me think that we are lumping several distinct diseases under the label of SARDS. In fact, that fits with the definition of a syndrome, which is “a set of clinical signs that occur together and are recognizably associated with a particular condition.” I wouldn’t be surprised if in the future a diagnosis of SARDS becomes obsolete and is replaced by one of several more specific diagnoses.
But in the meantime, what is consistent after a diagnosis of SARDS is the fact that blindness is permanent no matter what treatment is attempted (if it isn’t, the initial diagnosis must be reconsidered). When systemic clinical signs are present, the only one that appears to worsen over time is increased appetite, according to recent research.
The same study found that 37 percent of owners surveyed reported an “improved relationship with their dog after diagnosis, and 95 percent indicated they would discourage euthanasia of dogs with SARDS,” probably because dogs adapt so well to blindness, regardless of the cause.
Dr. Jennifer Coates
Dictionary of Veterinary Terms: Vet-speak Deciphered for the Non-Veterinarian. Coates J. Alpine Publications. 2007.
Long-term outcome of sudden acquired retinal degeneration syndrome in dogs. Stuckey JA, Pearce JW, Giuliano EA, Cohn LA, Bentley E, Rankin AJ, Gilmour MA, Lim CC, Allbaugh RA, Moore CP, Madsen RW. J Am Vet Med Assoc. 2013 Nov 15;243(10):1425-31.