Progressive Retinal Atrophy (PRA) has been described in more than 100 breeds of dog. This isa group of diseases characterized by a loss of night vision in the first few years of life (2 to 5 years). This night blindness is followed by a progressive loss of the peripheral visual field and finally a total loss of vision, involving an initial loss of rods and then cone photoreceptors. involved. Each PRA generally occurs in only one or a few breeds. PRA are naturally occurring retinal diseases in dogs, and have symptoms similar to that of
Retinitis Pigmentosa in humans. Retinitis Pigmentosa (RP) is the most prevalent group of inherited retinopathies in humans, affecting about 1 in 3600 individuals.
Three disorders of the retina have been described in Border Collie: the Collie Eye Anomaly (CEA, the Central Progressive Retinal Atrophy (CPRA) and the (non central) Progressive Retinal Atrophy (PRA). CEA is frequently diagnosed in Collie but less frequently in Border Collie. Moderately affected dogs present a normal vision throughout
life but in severely affected individuals, colobomas at the optic nerve can lead to retinal detachments and blindness.
A a new form of PRA has been identified in the Border Collie breed. The clinical signs, including the loss of night vision and a progressive loss of day vision, resulting in complete blindness, occur at the age of three to four years and may be detected earlier through systematic ocular fundus examination and electroretinography (ERG).
The new form of PRA occurring in Border Collie is a new X-linked PRA (XLPRA3). It has been proposed as a potential model for the similar human disease, XLinked Retinitis Pigmentosa.