The retina is the light-sensitive tissue in the back of the eye and is made up of photoreceptor cells called rods and cones. The rods are responsible for vision in low light conditions and the cone cells are responsible for vision in bright light. The retina captures the light that enters the eye and generates an electrical signal that gets relayed to the brain for "processing." Once the brain processes the information, we "see" a picture. Degeneration of the retina, regardless of cause, leads to loss of vision in animals. There are several potential causes of retinal degeneration.
Causes
This is an inherited disease - a condition with a genetic predisposition and one of many different types of inherited degenerative conditions. The age of onset is variable and can even affect young to middle-aged animals. Since the retina is predominantly made up of rods, the initial sign, in most animals, is a decrease in night or low light vision. This eventually progresses to include a loss of vision in daylight as well.
In the aging dog or cat, thinning of the retina may occasionally be seen during an eye examination. This thinning of the retina may be associated with some decrease in vision, however, owners may not appreciate any changes in vision or deficits in their pet.
Diagnosis
Diagnosis of retinal degeneration can be made by examination of the patient. The appearance of the retina may suggest or confirm the diagnosis, as the examiner may see evidence of thinning of the retina and its blood vessels and / or changes in the reflectivity of the tapetum (mirror-like structure in the retina of many animal species).
The diagnosis is confirmed by a test called an electroretinogram (ERG) which measures the electrical activity of the retina (a correlate with its function).
Treatment
Unfortunately, there is no treatment for retinal atrophy or degeneration. This is not a painful condition and most animals adapt quite well to their slow and progressive loss of vision. Caregivers of animals that lose their vision need to apply common sense when taking pets out of doors or in to unfamiliar environments where they don't know the lay of the land.
Prognosis
Retinal degeneration is a slowly progressive condition that can lead to blindness. Because animals are creatures of habit and become familiar with their normal surroundings, most pet owners don't even notice that their pet is losing vision until late in the course of things. It's usually when an animal is taken into unfamiliar surroundings that it becomes apparent. Animals that lose their vision can continue to function with their handicap and comfortably live to their natural lifespan in spite of blindness.
