Progressive Retinal Atrophy
Progressive Retinal Atrophy (PRA) is an inherited form of eye disease causing blindness. The first symptom is usually the loss of night vision. This can appear as early as 8 months of age but often does not show up until the dog is 3 to 5 years old. Owners often notice their dog is reluctant to go outside at night. In a dim room, they may not want to jump on or off furniture, and may not go up or down stairs. As the disease progresses the pupils become increasingly dilated, causing a noticeable "shine" to their eyes and the lens may become cloudy.
Dogs do not feel any pain or discomfort with the disease, however there is no cure or treatment, so owners must learn to live with their dog's condition. As vision deteriorates, affected dogs adjust as long as their environment remains constant.
Diagnosis of PRA is normally made by ophthalmoscopic examination. This is done using an instrument called an indirect ophthalmoscope and requires the dog's pupils to be dilated by applying eyedrops. Further confirmation can be made by electroretinography. This is an electrical measurement of retinal function. The ERG can only be recorded as a response to a flash of light and accurate recording of the ERG required the dog to be anesthetized. The ERG can also be used for early diagnosis, to detect affected dogs before they show clinical evidence of the disease. In Tibetan Terriers diagnosis can be made as early as 10 months.
Since PRA is a progressively degenerative disease, it is highly recommended that dogs have their eyes examined on an annual basis, starting at approximately 6 months and continuing until 8-10 years. This is especially true of those dogs that are being used for breeding purposes, however, there is benefit to the genetic health of the breed to test all littermates and offspring as well.