PRA is an autosomal recessive disorder, which means the pup had to receive one defective gene from both sire and dam. This also means that the pups parents would either become affected with PRA or are carriers of it. PRA has been recognized in most every breed of purebred dogs. (see chart: Inheritance of a Simple Recessive)

The disease affects the retina which is the tissue located inside the back of the eyeball. The retina shows a progressive thinning when examined with an opthalmoscope. This atrophy of cells diminishes the eyes ability to absorb and convert light.  All dogs affected with PRA display the same clinical abnormalities in the course of the disease: 1st) night blindness, 2nd) progressive loss of day vision, 3rd) eventual blindness.  At first the dog appears unable to adjust it's vision in dim light but sometimes the condition goes undiagnosed due to the dog's ability to adapt it's handicap by memorizing surroundings. Some owners detect the reflection of light in the increasingly dilated eyes.  Cataracts are common.  Diagnosis is best made by a veterinarian specializing in Opthalmology. The exam involves dilatation of the dog's pupil using special drops and use of an indirect ophthalmoscope.  The use of electroretinography may also be used to confirm diagnosis. This measures the retina's response to light. This test is most beneficial in early detection before the appearance of clinical evidence, for once this occurs its benefit is greatly reduced or lost