Progressive Retinal Atrophy in Sheep: Inherited Vision Loss

Progressive retinal atrophy, or more accurately inherited retinal degeneration, is a group of genetic eye diseases that damage the light-sensing cells of the retina over time. In many species, rods are affected first, so night vision declines before daytime vision. As the disease progresses, cones can also degenerate, leading to broader vision loss and eventual blindness.

In sheep, inherited retinal degeneration appears to be uncommon but documented. Published reports describe hereditary night blindness and progressive photoreceptor degeneration in some sheep lines, including Wiltshire sheep. Sheep can also develop retinal degeneration as part of other inherited disorders, so your vet will need to sort out whether the problem is an isolated retinal disease or part of a broader neurologic or metabolic condition.

For pet parents and flock managers, the practical takeaway is that this condition is usually slowly progressive rather than painful. Many sheep adapt surprisingly well in familiar surroundings, especially when housing, feeders, and flock groups stay consistent. The bigger concerns are safety, quality of life, and preventing the trait from being passed to future lambs.

The underlying cause is usually a genetic mutation that disrupts normal retinal function or photoreceptor survival. In inherited retinal disease, the retina may develop abnormally or may look normal at first and then slowly degenerate over months to years. Available sheep research suggests some forms behave like recessive inherited disorders, meaning clinically normal carriers can still pass the condition to lambs.

A published report in Wiltshire sheep described inherited night blindness with progressive rod photoreceptor degeneration, which closely resembles inherited retinal dystrophies seen in other species. Sheep have also been used as models for inherited retinal disease because naturally occurring mutations can affect cone or rod function.

That said, not every blind sheep has progressive retinal atrophy. Your vet may also consider toxins, nutritional problems, trauma, cataracts, infectious disease, scrapie-related changes, or retinal degeneration associated with other inherited neurologic disorders such as neuronal ceroid lipofuscinosis. This is why a careful exam matters before making breeding or management decisions.

Diagnosis starts with a full history and physical exam, including when the vision problem began, whether it is worse in low light, and whether related sheep have shown similar signs. Your vet will usually perform a basic eye exam, assess menace and pupillary light responses, and look for more common causes of blindness such as corneal disease, uveitis, cataracts, or trauma.

If retinal disease is suspected, your vet may recommend ophthalmoscopy to examine the back of the eye. In some cases, especially early in the disease, the retina can look close to normal even when function is already reduced. An electroretinogram (ERG) can help measure retinal function and may detect degeneration before obvious structural changes are visible.

Additional testing depends on the case. This can include bloodwork, neurologic evaluation, and sometimes referral to a veterinary ophthalmologist. In flock situations, pedigree review and discussion of related animals are important because inherited disease is often diagnosed through a combination of clinical findings, progression over time, and family pattern rather than one single test.

Because this condition is inherited, prevention focuses on breeding management rather than vaccines or supplements. Sheep that are affected should not be used for breeding. If more than one related animal shows night blindness or progressive vision loss, your vet may advise avoiding repeat matings from that line and reviewing flock records for patterns.

If a DNA test becomes available for a specific mutation in your breed or line, that can help guide mating choices. In many sheep populations, though, prevention still depends on careful observation, pedigree tracking, and removing affected animals and likely carriers from breeding plans when the evidence is strong.

It also helps to prevent confusion with non-genetic blindness. Work with your vet on sound nutrition, toxic plant control, parasite management, and prompt evaluation of eye injuries or infections. Those steps do not prevent inherited retinal degeneration itself, but they do reduce other causes of vision loss that can look similar early on.