What is collie eye anomaly?
Choroidal hypoplasia is also more commonly referred to as collie eye anomaly. This is a hereditary disease that can affect the Border Collie, the Rough Collie, the Shorthair Collie, the Lancashire Heeler or the Shetland Sheepdog.
In dogs affected by the disease, there is a mutation in a gene that is involved in the development of the eye, which leads to an abnormal development of the blood vessels that support the retina. In case of choroidal hypoplasia, both eyes are affected but sometimes to different degrees between the two eyes.
How is the disease transmitted?
The Collie eye anomaly is a disease:
- hereditary, which is transmitted from parents to descendants,
- monogenic i.e. linked to a mutation in a single gene,
- recessive i.e. which requires that both parents transmit the mutated gene to their offspring,
- autosomal, i.e. not linked to sex.
There are mild and severe forms of the disease. As these two forms are due to a mutation in the same gene, dogs with a mild form can give birth to offspring who will present a severe form.
How does the Collie's eye anomaly manifest?
In dogs affected by Collie eye anomaly, there is a great variability of clinical signs depending on the breeds affected and the individuals.
The mild form of the disease (grades 1 and 2) does not cause any visual discomfort and does not progress, while the severe forms (grades 3 and 4) are progressive and are accompanied by detachment of the retina and intraocular hemorrhages, which lead to visual loss that can go as far as the complete blindness of the animal.
However, although Collie eye anomaly can lead to blindness, the disease does not affect animal survival and most dogs adapt quite well to their vision loss. It is obviously necessary to adapt their environment in order to make their daily life easier.
The Collie's eye anomaly can be associated with other, sometimes more obvious, eye abnormalities such as microphthalmia.
Is there a treatment for COA?
Unfortunately, there is no cure for this condition although some abnormalities sometimes associated with collie eye anomaly, such as coloboma, may benefit from surgery to minimize the effects.
Are there means of prevention?
There is now a genetic test to detect dogs carrying the mutated gene responsible for the Collie eye anomaly. In breeds at risk, this test makes it possible to exclude from breeding dogs carrying two copies of the defective gene or to breed dogs which have only one copy of the defective gene (heterozygotes) with dogs not carrying the mutation. (he althy homozygotes).