Generalised Progressive Retinal Atrophy

Generalised progressive retinal atrophy (PRA) is aninherited disease which affects many breeds of dog.  Those breeds which are currently certified under the Eye Scheme, together with the approximate age at which an ophthalmoscopic diagnosis can be made, are listed in the table.  There are two main types of generalised PRA - rod/cone dysplasia and rod/cone degeneration.  The clinical and ophthalmoscopic signs for the two types are similar.  In a breed such as the Irish Setter, with rod/cone dysplasia, the photoreceptors are abnormally formed and begin to degenerate before they are mature.  The disease, therefore, affects these dogs at a relatively young age.  A DNA-based test for the gene mutation is available and enables accurate identification of clear, carrier and affected animals, but the Irish Setter is the only breed for which this test is currently available.  The age of onset is later in, for example, the rod/cone degeneration of the miniature and toy poodle, as the photoreceptors degenerate after reaching maturity.

Owners usually notice a loss of night vision, especially when the dog is in unfamiliar surroundings.  The condition progresses to produce a loss of vision under all lighting conditions and there is a por pupillary light reflex with dilated pupils.  In time, secondary cataract formation is common.  Ophthalmoscopic examination indicates a generalised, bilaterally symmetrical increase in tapetal reflectivity (a consequence of retinal atrophy).  There is attenuation (narrowing) of the retinal vessels, especially the small periphpillary arterioles, which may become barly visible ('ghost vessels') or disappear completely.  In dogs with a poorly developed tapetum or an atapetal dundus, the attenuation of the retinal vessels may be the only obvious ophthalmoscopic sign of early generalised progressive retinal atrophy, necessitating careful observation.  Later in the course of the disease the optic disc becomes paler due to atrophy of its capillaries and nerve fibres.  The non-tapetal fundus also shows extensive areas of depigmentation as the condition progresses.  The cataracts which form late on in the condition may manifest as opacities in the posterior cortex or as radial opacities, before progressing to total cataract. 

Significance:  There is no cure and the condition is one which progresses to total blindness.  In all the breeds which have been investigated in sufficient detail the mode of inheritance appears to be a simple autosomal recessive. 

Return to PRA Theory