Progressive Retinal Atrophy (PRA) Progressive retinal atrophy,
or PRA as it is frequently termed, is a hereditary eye disorder.
It is inherited as a simple autosomal recessive in most breeds.
PRA has been recognized in humans, in most purebred dogs and
some breeds of cats. PRA is a disease of the retina, a tissue
that is located inside the back of the eye. The retina contains
specialized cells called photoreceptors. These absorb the light
focused on them by the eye's lens, and convert the light into
electrical nerve signals. The nerve signals are passed by the
optic nerve to the brain where they are perceived as vision. In
PRA in Abyssinian and Somali cats, the photoreceptors degenerate
gradually. Early in the disease, night vision deteriorates as
the cat will face increased problems adjusting its vision to dim
light. Later in the process, daytime vision also fails. As the
retina degenerates it gets thinner and light will be strongly
reflected (hyper reflection). At the same time the pupils become
increasingl