Iris Coloboma is a hereditary condition affecting the eyes of dogs and manifested by the failure of the tissues of the eyes to develop fully while still inside the mother’s womb. A defect in the development results in the presence of a cleft or hole in the retina of the eyes. The retina is the colored spot on the center of the eyes.
When a dog has Iris Coloboma, there is a characteristic irregularly-shaped iris or a dark hole in the place where an iris should have been located. The iris performs a very important function, that of regulating the amount of light that enters the eyes.
Minor cases of Iris Coloboma only exerts a minimal effect on a dog’s vision however a large coloboma can reduce a dog’s vision, albeit temporarily, because the affected dog tends to squint in the presence of bright light in an attempt to lessen the amount of light reaching the eye. Iris Coloboma is a problem in herding dogs because their increased sensitivity to light and constant squinting often interferes in their daily activities.
Iris Coloboma is generally an inherited condition through recessive genes which are closely related to the genes that carry merle qualities. It can already be observed and diagnosed even when the newborn is still a few days old.
Aside from being a congenital defect, Iris Colobomas can be caused by trauma to the important tissues of the eye or as a complication following eye surgery.
In order to confirm initial diagnosis, your vet will perform a thorough eye examination which is best done on eyes which are non-dilated. There have been instances when small colobomas were not seen when the pupil was dilated during examination.
Dogs with Iris Coloboma should never be bred because it is a congenital disease. If you are buying a puppy, be sure to ask for a certification from the Canine Eye Registration Foundation (CERF). This certification will guarantee that your puppy is free from genes that carry Iris Coloboma. A reputable breeder also makes it his responsibility to have the litter undergo mandatory examination by a certified veterinary ophthalmologist when the puppies are six weeks old.
Iris Coloboma can affect any breed of dog, however, among Australian Sheepdogs, Collies, and Basenjis have been shown to be more prone to the condition. The condition may appear concurrently with other abnormalities affecting the eye including Persistent Pupillary Membrane (PPM), Distichiasis, Cataracts, detached retinas, and Progressive Retinal Atrophy (PRA).