When a dog inherits two copies of the merle gene it virtually always has serious eye defects. These dogs frequently are mostly white and may also be deaf. The condition is sometimes referred to as merle ocular dysgenesis. Some have called it Australian Shepherd Syndrome, but that is a poor term since the defects seen in double merle Aussies are also seen in double merles of other breeds. The merle gene is the same in all.
Any part of the eye can be affected. Irises are frequently deformed, sometimes grossly so. Pupils may be subluxated (off-center). The lens may be subluxated (out of place). The retina may be abnormal, and the optic nerve may be improperly developed. The entire globe of the eye may be abnormally small (microphthalmia). Most double mWhen erles will have a combination of these defects in each eye. They are frequently blind. All of this can be avoided by not breeding merle dogs to each other.