Progressive retinal atrophy (PRA) is a group of genetic diseases seen in certain breeds of dogs and, more rarely, cats.
Similar to retinitis pigmentosa in humans,[1] it is characterized by the bilateral degeneration of the retina, causing progressive vision loss culminating in blindness.
In general, PRAs are characterised by initial loss of rod photoreceptor cell function followed by that of the cones and for this reason night blindness is the first significant clinical sign for most dogs affected with PRA.
[3] Generalized PRA is the most common type and causes atrophy of all the neural retinal structures.
Commonly affected breeds:[4] This type of PRA has an early onset of severe vision loss.
It is caused by a defect in the gene for cGMP-phosphodiesterase, which leads to retinal levels of cyclic guanosine monophosphate ten times normal.
[4] Progressive vision loss in any dog in the absence of canine glaucoma or cataracts can be an indication of PRA.
Secondary cataract formation in the posterior portion of the lens can occur late in the disease.