PROGRESSIVE RETINAL ATROPHY

Michel (Mike) B. Rubini
Edited by Laura Fox
June 2014


Progressive Retinal Degeneration, better known as Progressive Retinal Atrophy (PRA) is a genetically autosomal recessive inherited group of diseases which causes irreversible degeneration of the Retina. General inheritance follows the same rules as PLL; each parent must have passed on the effected gene for the disease to develop in their offspring but inheritance rules can be different for some breeds.
 

There is also another form of PRA that does not appear to be inherited but seems random. This is called
Sudden Acquired Retinal Degeneration (SARD)

The Retina, which is part of the central nervous system, contains specialized cells (photoreceptors) that convert light into electrical impulses. These electrical signals are then transmitted by the Optic nerve to the brain for interpretation into images. There are two types of photoreceptors found in the retina;

rods which interpret Black and white images and are more sensitive to low light and cones that interpret color. Dogs depend mostly on rods for vision, Color vision in dogs is poor compared to human vision.

 

An eye exam by veterinarian can detect changes in the eye that are characteristic of PRA. The level of function in the animal’s retina can also be determined by an electroretinography, which measures the amount of electrical activity of the retina in response to light shining on it.


When PRA asserts itself retina degeneration generally begins with the rods. Thus the earliest problems exhibited by the animals will be a loss of night vision. Although the diseases progression can depend on the type of PRA, the breed and even the individual animal the disease generally leads to total blindness within a couple of years. As the disease progresses a ‘shine’ may be noticed in the animals eyes. This is due to the pupils being dilated and not responding the amount of light as it normally should. The animal will not experience any pain with PRA!


There are several genetically different variations of PRA all caused by a different mutation in a specific gene causing PRA. Although some mutations are specific to a breed, many breeds can share the same PRA gene mutation. Each individual case can be different and initial age of affliction will often determine the progression of the disease. Genetic testing should be performed to verify if the disease is genetic in nature.


New DNA tests for various forms of PRA for specific breeds and genes are constantly being developed.


GENERAL PRA – The bilateral general degradation or degeneration of the retina causing blindness.


LATE ONSET PRA - Onset of the disease usually begins about the ages of 3 to 5 years old but sometimes as late as 10 years. It always results in complete blindness usually within a couple of years.


EARLY ONSET PRA -. Onset of this type of PRA can start as early as 6 weeks old. With early onset PRA In this disease rods and cones do not develop normally in the puppies and will start to degenerate shortly after, usually leading to total blindness in 2 to 3 years.


CENTRAL PROGRESSIVE RETINAL ATROPHY– A separate disease also known as RETINAL PIGMENT


EPITHELIAL DYSTROPHY and is a gradual degeneration of the coating of the Retina (pigmented Epithelium) so losing its  considerably long time. This is not a common disease. 

 

There is no cure for Progressive Retinal Atrophy. Once the animal is afflicted it will go blind. Since it
takes some time for the disease to progress the animal does have time to adjust to the vision loss.
Stability in its habitat is essential at this point.


Cataracts can often form in the later stages of PRA because of chemicals released into the eye by the
degenerating retina. While complicating the diagnosis it will not help the animal’s vision to remove the 
cataracts.
But because Cataracts can cause other problems in the eye including possibly PLL and
Glaucoma the situation should be monitored and perhaps treated.


It may be that ‘anti-oxidants’ and the consumption of Lutein may slow the progress of the disease if
taken early enough. However, it is unknown if they can be of benefit at this time. In most cases the
disease will have progressed to a more advanced stage where Vitamins and Lutein may be of little help.


Note – Note that all types of the known inherited PRA is a autosomal recessive gene except for these
two exceptions. The Bull Mastiff PRA inheritance is an autosomal dominant inheritance. The Siberian
Husky is a sex (X chromosome) linked recessive inheritance trait.


June 2014
Michel (Mike) B. Rubini mike@rubini.ca
Edited by Laura Fox
Website Terralea Collins
There is no cure for Progressive Retinal Atrophy. Once the animal is afflicted it will go blind. Since it

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