What are cataracts?
A cataract is an opacity of the lens, which sits just behind the pupil in the eye. Most hereditary cataracts in Aussies arise in the center of the back of the lens, referred to as posterior polar.
Are cataracts hereditary?
They can be. Aussie hereditary cataracts almost never occur in young puppies; affected dogs most commonly present signs as mature adults, though cataracts may start in early adulthood or not until old age. Cataracts can occur for reasons other than heredity (other diseases, injury, or nutritional imbalance) but these other causes are not common and should not be assumed to be the reason unless confirmed by a veterinary ophthalmologist.
How do I know if my dog has cataracts?
Very advanced cataracts can be seen without any special equipment. The pupils will be somewhat dilated and appear milky white. However, most cataracts are detected during exam. 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 six months to a year to see if one develops in the other.
What are suture line cataracts?
The sutures are two Y-shaped structures on the front and back of the lens where the tissue came together during development. Occasionally a cataract may develop at the site of these sutures.
What do cataracts mean for my dog?
. Hereditary cataracts progress starting as small opacities and advancing, sometimes to the point of clouding the entire lens. Dogs with these generalized cataracts are unable to distinguish anything but extremes of light and dark. Cataracts do not cause the dog any pain and usually progress slowly enough that the dog adjusts to its vision loss. Some dogs progress very slowly and have functional vision throughout their lives. Cataract surgery can be performed, but it is expensive and not always successful.
How common are cataracts in Aussies?
Roughly 2% of Aussies will develop cataracts. They are the most common eye disease in the breed.
Are merles more likely to develop cataracts?
No more likely than tris! There has been no evidence that cataracts correlate with coat color in any breed of dog.
Are cataracts inherited in Aussies?
In most cases. The mode of inheritance for most Aussie cataracts is dominant with incomplete penetrance, meaning not every dog with the mutation will develop cataracts though 70% of those with cataracts have it. The remaining hereditary cataracts are caused by as yet unidentified genes.
Cataracts may be acquired if the eye is injured or has an infection or other condition that causes inflammation within the eye. Dogs may also develop nuclear sclerosis as they get old, a hardening of the nucleus of the lens that turns it opaque.
Is there a DNA test for cataracts?
Yes. There is a test for a dominant mutation of a gene called HSF4. This mutation is extremely common in the breed. Dogs with two normal copies of the gene will not develop this type of cataract. Dogs with one or two copies of the mutation have a heightened risk for developing cataracts.
What do cataracts mean for my breeding program?
Because the HSF4 mutation is only a risk factor and because there are hereditary cataracts that are not caused by HSF4, all breeding stock should receive annual exams by a veterinary ophthalmologist. Because the HSF4 mutation is so common, eliminating all dogs that have it from breeding is not an option. Dogs with cataracts should not be bred; if semen has been stored from males that develop hereditary cataracts it should be discarded. Normal dogs with the mutation should be bred only to clear-tested dogs and preference given to clear-tested offspring to carry on with. Relatives of affected dogs whose cataracts were not due to HSF4 or for which HSF4 status is unknown should be bred to clear mates with no recent family history of non-HSF4 cataracts or cataracts not clearly known to be HSF4.
Do dogs that are blind from cataracts need to be euthanized?
Absolutely not! Most blind dogs cope very well. Blind dogs memorize their home turf. If you move furniture or other large objects in the house or yard, you need to show your dog what you changed by taking him to the new or newly positioned object. Never let him wander off lead in an unfenced area. Keep an eye out for traffic, obstacles or other animals and things that he might blunder into. Give the dog basic obedience training: A rock-solid “freeze” command – down, sit, or something else that will stop the dog from moving – command could save his life. This could be “down,” “sit,” or whatever.
I know someone whose dog was diagnosed with punctate cataracts but it passed its eye exam. How can a dog with cataracts pass?
Punctate cataracts are very small and may not be inherited. Lens opacities occur for a variety of reasons, not all of them genetic. Our typical hereditary cataract is in the posterior cortex (back side of the lens in the outer layer of tissue.) It will be bilateral, though both eyes may not start to show them at the same time. The cataracts will advance over time. They usually begin between 2-5 years of age, but may start earlier or later.
A dog with posterior punctate cataracts might be in the early stages of hereditary disease and should have the DNA test for the HSF4 cataract mutation. If it is clear for HSF4, re-check it after 6 months to a year to see if the cataracts had advanced. If they have not, the opacities were probably non-hereditary.
Are nuclear cataracts inherited?
Probably not. Aussie inherited cataracts are usually in the cortex (outer layer of the lens) and on the back side. Nuclear cataracts are probably caused by something else—injury, disease, or environmental factors. The appearance and location of acquired cataracts is usually different from the inherited kind. A veterinary ophthalmologist should be able to tell.