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What is PRA?
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Progressive retinal atrophy or degeneration (PRA or PRD) is the name for several diseases that are progressive and lead to blindness. First recognized at the beginning of the 20th century in Gordon Setters, this inherited condition has been documented in over 100 breeds, and mixed breed animals as well. PRA is not common in cats. The eye is a very delicate, yet surprisingly durable organ. It consists of several layers. The cornea is a transparent layer that covers the front of the eye The iris is the coloured part of the eye and it is responsible for letting in more or less light The lens gathers and bends light in order to focus it on the retina. In between the cornea and lens is an area of fluid which bathes the lens and helps it focus. The retina lines the inside of the eye and converts light signals which travels down the optic nerve to the brain. A large area between the lens andthe retina contains a jelly like fluid called 'vitreous'. The vitreous gives the eye its form and shape, provides nutrients and removes waste products. The retina is the structure affected in PRA. This importantpart of the eye receives the light gathering and focused by the other eye structures. It takes the light and essentially converts it into electrical nerve signals that te brain, via the optic nerve, interprets as vision. The retina contains photoreceptors, called rods and cones, which helps the animal see in the darkness (rods) and see certain colours(cones). There are multiple forms of PRA which differ in the age of onset and rate of progression of the disease. Some breeds experience an earlier onset than others; other breeds do not develop PRA until later in life. Normally, the photoreceptors in the retinadevelop after birth to about eight weeks of age. The retinas of dogs with PRA either have arrested devlopment (retinal dysplasia) or early degeneration of the photoreceptors. Retinal dysplastic dogs areusually affected within two months of birth and may be completely blind by one year. Dogs with retinal degeneration are affected from one year to eight years of age and the symptons progress slowly. PRA worsens over time. The affected animal experiences night blindness initially because the rods are affected first. The condition progresses to failed daytime vision. Signs may vary depending on the type of PRA and its rate of progression. PRA is a non painful and outward appearence of the eye is normal. i.e. no redness, excess tearing, or squinting. Owners may notice a change in personality of their dog such as a reluctance to go down stairs or down a dark hallway. This is characteristric of night blindness, in which vision may appear to improve during the daytime. As the disease progresses, owners can observe a dilation of the pupils and the reflection of light from the back of the eye. If the blindness is progressing slowly, the owner may not notice any signs until the dog is in unfamiliar surroundings and the lack of vision is more apparent. In some animals the lens of the eyes may become opaque and cloudy. Ultimately the dog will end up going blind. When buying your puppy ask to see the documentation for the DNA testing for PRA of the parents. Two parents that are 'A's or 'Clear 'of PRA will have only progeny that is 'Clear by Parentage'. |
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