Progressive Retinal Atrophi (PRA)

Description
PRA is a disease of the retina. This tissue, located inside the back of the eye, contains specialized cells called photoreceptors that absorb the light focused on them by the eye’s lens, and converts that light, through a series of chemical reactions into electrical nerve signals. The nerve signals from the retina are passed by the optic nerve to the brain where they are perceived as vision. The retinal photoreceptors are specialized into rods, for vision in dim light (night vision), and cones for vision in bright light (day and color vision). PRA usually affects the rods initially, and then cones in later stages of the disease. In human families, the diseases equivalent to PRA (in dogs) are termed retinitis pigmentosa.


Symptoms/Clinical Signs
In all canine breeds PRA has certain common features. Early in the disease, affected dogs are night blind, lacking the ability to adjust their vision to dim light; later their daytime vision also fails. As their vision deteriorates, affected dogs will adapt to their handicap as long as their environment remains constant, and they are not faced with situations requiring excellent vision. At the same time the pupils of their eyes become increasingly dilated, in a vain attempt to gather more light, causing a noticeable "shine" to their eyes; and the lens of their eyes may become cloudy, or opaque, resulting in a cataract.


Diagnosis
An eye certification examination is done by a veterinarian specialized in ophthalmology. The types of abnormalities that may be noticed during the exam include distichia (extra eyelashes), imperforate puncta (not opened tear ducts), cataract (opacity of the lens), and vitreal degeneration, Progressive Retinal Atrophy (PRA), Retinal Dysplasia and retinal detachment.

At a minimum all dogs used for breeding should have eye certification examinations. Also it is beneficial for breeding programs if as many dogs as possible are checked, as this increases the likelihood of tracing carriers which themselves might not be inflicted with any disease.


Treatment & Prognosis
There is no treatment for PRA.


Inheritance
It is inherited as a simple autosomal recessive. PRA has been recognized in most purebred dogs.