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Sudden Acquired Retinal Degeneration Syndrome in Dogs

 

Sudden acquired retinal degeneration syndrome in dogs, often abbreviated as SARDS, is an eye condition that has been known to cause complete and typically irreversible blindness in affected dogs. Dog owners may notice behavioral changes suggestive of vision impairment such as bumping into furniture more or the dog acting jumpy and getting easily startled. Following is a case-based article going over how a typical case of sudden acquired retinal degeneration syndrome in dogs would present and be handled by a veterinarian presented by veterinarian Dr. Eric Weiner.

Vet checks a dog’s eye

An Example of a Case Study

Parker is an 8 year old female spayed mixed breed dog. She presents to her primary veterinarian for suddenly bumping into things. There is no history of previous eye issues and no known traumatic events. Upon further questioning, the owners have recently noticed an increase in thirst (polydipsia, PD) and frequency of urination (polyuria, PU), also known as PU/PD.

There has been no significant coughing, sneezing, vomiting, or diarrhea. Parker is up to date on all vaccines, current on heartworm, flea and tick preventatives and not on any other medication. Her temperature, respiration and pulse rates are within normal limits. Parker has gained 3 pounds recently and is determined to be overweight.

As the veterinarian is speaking with the owner, he observes Parker walk around the room. Parker bumped into the chair and is walking the perimeter of the room. On physical exam, the veterinarian notices that her eyes are dilated and do not constrict with a bright light. An indirect ophthalmic lens was used to visualize the back of the eye (fundic exam) and evaluate structures such as the optic nerve, retina, and tapetal reflection (that ‘deer in the headlights’ glow). No abnormalities are seen.




There is moderate gingivitis and dental calculus accumulation, with mild halitosis (bad breath). The ears are clean and two normal eardrums are seen. There is no cough elicited when massaging the windpipe, and superficial lymph nodes are normal. The doctor then listens to her chest with his stethoscope. The heart sounds, rate, and rhythm are normal. The lungs are clear and no crackles or wheezes are heard. There are no abnormalities detected on abdominal palpation. The doctor flexes and extended Parker’s joints and determines she has normal range of motion.

The problem list includes sudden blindness without physical abnormalities within the eye, PU/PD, dental disease, and overweight. Possible causes of sudden blindness that need to be considered include, but are not limited to, glaucoma or uveitis, retinal detachment, progressive retinal degeneration (PRD), optic neuritis, Sudden Acquired Retinal Degeneration Syndrome (SARDS), and central blindness.

Common rule outs for PU/PD in dogs include urinary tract infection, kidney disease, diabetes, and Cushing’s Disease (hyperadrenocorticism).

A Sample of a Diagnostic Work-Up 

A dog’s eye stained with fluorescein. In this case, there is an ulcer. Source: Joel Mills,Wikipedia,

Routine lab work is consistent with Cushing’s disease. The lab values do not support the other differentials for PU/PD. Tear production is measured and deemed normal. The eyes were stained with a fluorescent stain that sticks to the inner layers of the cornea. There was no stain uptake, making corneal ulcers or scratches unlikely.

The intraocular pressure, or pressure within the eye, was measured with tonometry and found to be within normal limits. This rules out glaucoma (high pressure) and uveitis (low pressure). The sudden onset of blindness rules out progressive retinal degeneration (PRD), which typically occurs over 6-24 months (Turner 2008).

The lack of abnormal structural findings (normal retina, normal optic nerve, etc.) rules out optic neuritis and retinal detachment, which would be evident upon evaluation of the back of the eye (fundic exam). Central blindness (a disconnect between information gathered from the eyes and how the brain perceives it) is not supported by any physical exam finding, neurologic evaluation, or lab result. This leaves SARDS and Cushing’s remaining on the differential list.

Sudden Acquired Retinal Degeneration Syndrome in dogs presents as complete and typically irreversible blindness that can occur overnight or up to a week or so. It most commonly affects older, small breed, overweight female dogs. However it can be seen in any breed, sex, or age, and has been documented in cats (Turner 2008). Owners commonly notice their dog has been bumping into furniture more, or is more easily startled. These dogs may also show signs of PU/PD, consistent with Cushing’s Disease. The cause of SARDS is unknown. Autoimmune, degenerative, infectious or inflammatory causes have been suspected, but not proven (Herring and Morgan, 2007 updated 2014).




Physical exam findings consistent with SARDS include dilated pupils that do not respond to light normally, also known as an absent pupillary light reflex or PLR. However the fundic exam is typically normal (no retinal detachment or degeneration is seen initially). Electroretinography, measuring the electrical activity of the retina, is required to make a definitive diagnosis.

Most primary care veterinarians do not have this equipment on site and need to refer to a board certified veterinary ophthalmologist. Electroretinography shows absent or ‘flat line’ activity of the retina. In contrast, there would be normal activity in an eye suffering from optic neuritis (inflammation of the optic nerve).

Although clinical signs (PU/PD) and lab work are consistent with Cushing’s Disease, a direct correlation between that and SARDS has not been established (Herring and Morgan, 2007 updated 2014). Further discussion of Cushing’s is beyond the scope of this article.

Sudden acquired retinal degeneration syndrome in dogs
Progression of sudden acquired retinal degeneration syndrome in dogs leads to irreversible blindness

Treatment of Sudden Acquired Retinal Degeneration Syndrome in Dogs

Unfortunately, there has been no effective treatments to restore vision in dogs suffering from SARDS. Studies from Iowa State University showed that the disease was due to autoantibodies that attacked the retina, and a human blood product known as immunoglobulin had been successfully used to treat this disease (Grozdanic S. D., Harper, M. M., and Kecova, H. 2008).

Unfortunately these findings have not been able to be repeated (Herring and Morgan, 2007 updated 2014), and prognosis for vision restoration is grim.

Managing sudden acquired retinal degeneration syndrome in dogs includes blocking staircases to avoid falling, maintain familiar environments (avoid rearranging furniture), and using a short leash to guide them when in unfamiliar territories.

Treating the Cushing’s diseases is somewhat controversial. The most recent literature this author has found recommends not to start treatment initially, but to retest in three months (Herring and Morgan, 2007 updated 2014). If the tests and clinical signs are still consistent with Cushing’s Disease, then initiate appropriate therapy at that time.

Due to the suspicion that SARDS may be caused by an autoimmune disease, starting steroids for their immune suppressing properties may be tempting. This however may be contraindicated as it could exacerbate the clinical signs of Cushing’s, and has not been shown to be effective previously.

The progression of sudden acquired retinal degeneration syndrome in dogs includes irreversible blindness. Veterinarians may notice degenerative changes to the retina on fundic exams months to years after the onset of disease. The good news is this is not a painful disease. Dogs generally adjust very well, and can go on living happy lives for years to come.




References

  • Grozdanic, Sinisa D., Harper, Matthew M., and Kecova, Helga. 2008. Antibody-Mediated Retinopathies in Canine Patients: Mechanism, Diagnosis, and Treatment Modalities. https://doi.org/10.1016/j.cvsm.2007.12.003.
  • Herring, Ian. 2007. Sudden Acquired Retinal Degeneration. Updated by Morgan, Rhea V. 2014. https://www.vin.com/Members/Associate/Associate.plx? from=GetDzInfo&DiseaseId=174.
  • Turner, Sally M. 2008. Small Animal Ophthalmology. Saunders. pp 299-301.

Photo Credits:

Wikipedia, Joel Mills, Refractory corneal ulcer in a Boxer.CC BY-SA 3.0

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