Collie eye anomaly or collie eye defect is a genetic congenital defect due to mutated chromosomes that determine the development of the eyes. This causes the choroid to under-develop. Choroid is the collection of blood vessels that absorb scattered light and nourish the retina. The mutation can also result in other defects like retinal detachment. It is always in both eyes although it might be more severe in one eye than the other. Besides Collies it is also seen in Australian Shepherds, Shetland Sheepdogs, Lancashire Heelers, and other herding dogs.
The condition could remain asymptomatic until the actual onset of blindness. Some associated conditions that may occur with this defect are
Microphthalmia, where the eyeballs are noticeably smaller than normal;
Enophthalmia, where the eyeballs are abnormally sunken in their sockets;
Anterior corneal stromal mineralization, the connective tissue of the cornea (the transparent coat at the front of the eye) becomes mineralized and shows as a cloud over the eyes;
Retinal folds, where two layers of the retina do not form together properly. This may not be very obvious on inspection