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Dog: Progressive Retinal Atrophy

General information

Other common/scientific names: PRA

The retina is a highly specialized sheet of nerve tissue located in the back of the eye made up of several layers. The photoreceptor layer contains two different types of cells: rods which are associated with night vision and cones which are associated with day and color vision. Dogs have more rods than humans to allow for better vision in dim light. The retina converts light into vision by creating an electrical impulse. This impulse passes through the layers of the retina to the optic nerve which leads to the visual cortex in the brain. The impulse is analyzed in the brain where it is interpreted into visual images. Without a normal functioning retina, vision is not possible.

Abb. GGEUBCQU
Abb. GGEUBCQU: Schematic illustration of the eye, side view.
The retina is colored in yellow and lines the entire back part of the eye.

Progressive retinal atrophy refers to a broad category of mostly inherited retinal diseases that result in blindness in dogs. As the name implies, this disease is progressive and leads to blindness. In the category of PRA, there are different clinical forms which affect different breeds.

Causes

Most cases of retinal atrophy are inherited. Some breeds which are affected include: Miniature Poodle, English and American Cocker Spaniel, Tibetan Terrier and Alaskan Malamute.

Cardinal symptom

Vision Loss

Symptoms

With progressive retinal atrophy, the photoreceptor cells undergo atrophy or degeneration. In the most common form, the rod cells are affected resulting in vision loss in dim light or night blindness. This can cause dogs to be fearful to go outside at night. As the disease progresses, the pupils will dilate and have a slow response to light. A dog with PRA will become completely blind even during the daylight hours. Cataracts may develop in the late stages of PRA due to toxins released from the degenerating retina.

Vision loss can be sudden and progress rapidly or it can occur more slowly over a time span of several years.

Often, vision loss goes unnoticed by the owner until a change in the dog’s environment occurs such as rearranging the furniture. Dogs will develop their sense of smell and hearing to compensate for the loss of sight. PRA is not painful or life threatening.

Diagnosis

Progressive retinal atrophy is diagnosed by a complete ophthalmic examination. While early detection is possible by an experienced veterinary ophthalmologist, in many cases, PRA goes undetected until the disease has progressed. A specialized test called an electroretinogram (ERG) can be performed to definitively diagnose PRA. This test is used only by veterinarians specializing in ophthalmology. An ERG measures the electrical impulses in the retina which allows affected dogs to be diagnosed before they show clinical signs.

Treatment

There is no known treatment for progressive retinal atrophy.

Prognosis

The prognosis is poor for vision.

Prevention

Because of the hereditary nature of PRA, affected dogs should not be used for breeding. Genetic testing is available in some breeds to detect carriers of PRA. Dogs can be carriers of PRA and not show any clinical signs. Because of this, pedigree studies are indicated to eliminate the spread of PRA to carrier offspring.

Tips

If your dog has reduced vision or is blind due to PRA, he/she can have a good quality of life. It is important not to rearrange the furniture or leave hazardous clutter in the home. Be aware that some dogs do become more anxious or even aggressive when they lose their vision.

Update version: 4/24/2014, © Copyright by www.enpevet.de
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