In SARD, the retina is damaged rapidly (i.e. a matter of days) and results in an incurable loss of vision.
The functioning of the eye is analogous to that of a camera. Like a camera lens, the lens of the eye focuses images and light from the outside world. The light is transmitted through the lens and onto the retina, a thin membrane positioned at the back of the eye which acts like the film of a camera. Light rays are converted into electrical impulses and are sent through the optic nerve to the brain, where images are actually perceived. In SARD, the retina is damaged rapidly (i.e. a matter of days) and results in an incurable loss of vision. An electroretinogram (ERG) performed by an ophthalmologist is required to definitively diagnose this disease. While the sudden loss of vision is devastating, the disease process is non-painful and most animals will adjust to the handicap over time with the help of their owners. The cause of SARD is unknown and there is no validated treatment currently, but research of this disease is one of the top priorities of the Vision for Animals Foundation (VAF).
What is an electroretinogram?
An electroretinogram (ERG) is a diagnostic test performed to determine whether or not the retinas are healthy. The ERG measures the electrical response of the retina after a light is flashed in front of the eye. The response, or lack thereof, is recorded on a computer screen. A healthy ERG recording looks similar to the tracings of a heart monitor, or electrocardiogram (ECG). A healthy retina produces a wave of a known amplitude. The patient’s ERG tracing is compared to what is known to be normal to determine whether the retina is functioning properly.
With SARD, the ERG tracing appears as a flat line; i.e, no recordable wave form.
American College of Veterinary Ophthalmologists: More information on SARDS
Vision for Animals Foundation: About SARDs
Vision for Animals Foundation: 2015 SARDS Review Article – Veterinary Ophthalmology Journal