09/02/2026
Merle Ocular Dysgenesis (MOD) is a hereditary condition present from birth, most often seen in dogs with a double merle (double dapple) genetic pattern.
Dogs with MOD may have small or underdeveloped eyes, abnormal irises or pupils, cataracts, and retinal or optic nerve defects like poor development or detachment. The double merle gene can also affect hearing, and some MOD dogs are born deaf.
Because the eye doesn't develop correctly before birth, multiple eye structures can be affected ranging from mild abnormalities to complete blindness.
MOD is linked to breeds like Australian Shepherds, Dachshunds, Great Danes, Old English Sheepdogs, American Foxhounds, and Catahoula Leopard Dogs, though mixed-breed dogs can be affected too.