Australian Shepherds, along with several other mostly collie-type breeds, can carry genetic eye mutations.

Hereditary Cataracts (HC)
the HSF4 mutation.

by C.A. Sharp

Cataracts are the most common eye disease in Australian Shepherds. They can occur for reasons other than heredity (other diseases, injury) but these other causes are not common and should not be assumed to be the reason for cataract without clear evidence to that end.

Hereditary cataracts are bilateral, meaning they occur in both eyes, but they may not appear at the same time: If a cataract is noted on one eye, it is wise to recheck in 6 months to a year to see if one develops in the other. Cataracts progress, starting as small opacities and advancing, sometimes to the point of clouding the entire lens and reducing vision to an inability to distinguish anything but extremes of light and dark. Cataracts do not cause the dog any pain and usually progress is slow enough that the dog adjusts to its vision loss. In Aussies cataracts virtually never occur in young puppies. Affected dogs most commonly present signs between 1.5 and 3 years of age, but may first show disease as late as 7 or 8 years of age. This wide range in the age of onset makes the disease extremely difficult to predict or eliminate.

Cataracts are classified by where in the lens they first develop. The lens is round when viewed from the front or back, thickest in the middle and tapering to the outer edge. The front is referred to as the anterior; the back is the posterior. The inside is the nucleus; the outside, the cortex, and the outer (round) edge, the equator. The center of the lens is the polar area. So, if a dog has posterior polar cortical cataracts, they are forming on the back side in the center on the outer layer. This is where the vast majority of Aussie cataracts start.

The mode of inheritance appears to be dominant with incomplete penetrance, meaning not every dog with the mutation will develop cataracts. It is also extremely variable in the age of presentation. It is possible that some dogs that ultimately are or would have been affected are not detected because they die first or the owner stops doing eye exams before the cataracts develop.

All breeding stock must be examined by an ACVO vet annually. Affected animals should not be bred. If they have produced offspring prior to diagnosis, owners of those offspring need to be told. Parents, siblings and offspring of affected animals should only be bred with care--never to their relatives or dogs from lines where cataract is known to be a problem.

Progressive Retinal Atrophy (PRA)

The genetic disorder Progressive Rod-cone Degeneration-Progressive Retinal Atrophy, causes cells in the retina at the back of the eye to degenerate and die, even though the cells seem to develop normally early in life.

The result is declining vision and eventual blindness. The “rod” cells operate in low light levels and are the first to lose normal function. Night blindness results. Then the “cone” cells gradually lose their normal function in full light situations. Most affected dogs will eventually go blind. It’s important to remember that not all retinal disease is PRA and not all PRA is the prcd form of PRA. DNA testing will make the diagnosis, prior to the onset of disease.  

PRA refers to a group of diseases that cause the retina of the eye to degenerate slowly over time. The result is declining vision and eventual blindness. The acronym "prcd" stands for "progressive rod-cone degeneration" which is the type of PRA known in several breeds. The “rod” cells operate in low light levels and are the first to lose normal function. Night blindness results. Then the “cone” cells gradually lose their normal function in full light situations. Most affected dogs will eventually be blind.

Typically, the clinical disease is recognized first in early adolescence or early adulthood. Diagnosis of retinal disease can be difficult. Conditions that seem to be prcd-PRA might instead be another disease and might not be inherited.  Genetic testing assists in making the diagnosis. It’s important to remember that not all retinal disease is PRA and not all PRA is the prcd form of PRA. Annual eye exams by a veterinary ophthalmologist will build a history of eye health that will help to diagnose disease.