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Sudden Acquired Retinal Degeneration (SARDS)

 

Veterinary ophthalmologists are aware of a vision loss syndrome associated with changes in appetite and water consumption in dogs. This condition, known as sudden acquired retinal degeneration syndrome (SARDS), may strike any pure or mixed breed of dog. These pets are generally between the ages of 7 and 14 years of age, with females predominating over males. Research indicates these pets have total destruction of the visual cell layer (the rods and cones) of the retina with subsequent blindness.

Typically the onset of visual loss is sudden. In some cases it is noticed virtually overnight. In other cases observant owners may notice a degree of visual aberration for 5 to 10 days before complete loss of vision becomes apparent. Very typically the owners will report an often dramatic increase in drinking and appetite in the weeks before onset of visual loss. In many cases the weight will have increased in that time. Some owners report a concurrent decrease in hearing and smell.

Examination by a veterinary ophthalmologist reveals that the patient has a normal appearing retina. The pupils are generally dilated and non-responsive to light but in some cases the pupillary light response will be present but sluggish and incomplete. The menace response is generally absent, and the dog will fail to track a dropped cotton ball.

A routine blood and urine work up in these patient may reveal changes which are suggestive of hyperadrenocorticism (Cushing's Syndrome). If these tests are followed up with specific testing for Cushing's (low dose dexamethasone suppression test, ACTH stimulation test) some cases will be confirmed as Cushingoid. These patients should be treated for their Cushing's syndrome, but this will not restore vision. The relationship between Cushing's syndrome and SARDS is not known.

The problem with cases of acute blindness is that other diseases must be considered as the cause. These include optic nerve inflammation (optic neuritis), tumours invading or pressing on the optic nerve or optic chiasm, brain tumors or inflammations, and SARDS. There has been recent discussion that various types of blood pressure abnormalities and conditions where the lipid levels in the blood (hyperlipidemic syndromes) may produce an occult visual loss syndrome similar to SARDS. The final diagnosis of SARDS in these cases involves a thorough blood and urine profile, blood pressure measurement and a test of retinal function known as an electroretinogram (ERG). If the retina is working normally as demonstrated by a normal ERG, then the diagnosis is not SARDS and further tests are needed to determine the true diagnosis. If the ERG is flat and the blood pressure is normal, then SARDS is the most likely diagnosis.

There has been considerable work done to understand the pathophysiology of SARDS. Sudden and rapid cell death of neural cells is generally associated with a phenomenon called apoptosis. Every cell in the body carries a gene which governs cell division, and another gene which governs cell death. Chemical messengers are involved in initiating activity of these genes. So it appears that an unknown trigger sets off a biochemical cascade resulting in massive apoptosis of the rods and cones. Indeed, this is a similar mechanism to the cause of brain cell death in humans with Alzheimer's and Parkinson's disease, and is similar to the ongoing retinal cell death in glaucoma even when the intraocular pressure is controlled effectively.

As with other types of retinal degeneration, SARDS has no treatment. Examination of tissue specimens has indicated that the visual cell layer of the retina is destroyed and cannot regenerate. The reason the diagnosis is important is that if optic neuritis is causing the blindness, anti-inflammatory treatment may restore vision. If a brain tumor is determined to be present, then radiation therapy may be necessary to save your pet's life. For these reasons, finding the cause of sudden blindness is important.

Although veterinary ophthalmologists do not know the cause of and cannot treat SARDS, you should know that this is not a painful condition. Your pet is not in pain. Your pet is just confused as you would be if you suddenly became blind. How you should treat a pet who is blind is the subject of another page on this website:

A few years ago, veterinary ophthalmologists conducted a survey by giving an in-depth questionnaire to owner of dogs with confirmed cases of SARDS. This effort failed to reveal any common environmental factor which would allow us to understand this perplexing disease.