Iris Coloboma in Dogs

Iris Coloboma affects a dog's eyes and therefore their vision. It's a hereditary condition that any breed of dog can suffer from although certain breeds seem to be more predisposed to inheriting the disorder than others. The problem with a dog's eyes starts when puppies are still in their mother's wombs when the tissues found in the eye fails to develop as they should. This results in a hole or cleft in a dog's retina which is characterised by an irregular shape of the iris or a dark spot where the iris should be.

The iris has a very important function in that it regulates the amount of light that enters a dog's eyes so when the problem is just slight, it will not impact their vision to any worrying extent. However, if an Iris Coloboma is larger, a dog's vision could be seriously impacted momentarily because to counterbalance the effect, a dog must squint which then lessens the amount of light that's allowed to enter their eyes. Working dogs and more especially herding breeds have more of a problem if they suffer from the condition because they are more sensitive to light and just the act of having to squint interferes with their work being “eye dogs”.

A Hereditary or Acquired Condition

The genes responsible for a dog having Iris Coloboma are recessive and are similar to the merle gene. However, the condition can be acquired too more especially if a dog has suffered some sort of trauma to the eye. Dogs can develop them due to a complication that occurred during some form of eye surgery that was performed on their eyes.

Some Breeds More Susceptible than Others

Although, as previously mentioned, any dog can develop or be born with an Iris Coloboma, there are certain breeds that are known to be more predisposed to inheriting the condition than others and this includes the following:

• Australian Sheepdog
• Collies
• Basenji

A lot of the time, the condition can develop at the same time as other eye abnormalities which includes when dogs suffer from Pesistent Pupillary Membrane (PPM), Distichiasis, Cataract, Progressive Retinal Atrophy or their retinas become detached.

Diagnosing the Problem

It's important for vets to have a dog's full medical history before they carry out any sort of eye examination. Once they have this information to hand, they would need to thoroughly examine a dog's eyes to confirm whether they have developed an Iris Coloboma or whether they were born with the condition. To do this effectively, a dog's eyes must be non-dilated because smaller colobomas can go unnoticed when the pupil is dilated. When examining the eye, a vet might find that a dog has developed “iris hypoplasia” which is a thinning of the tissue found in the iris and although it is not known whether this is milder form of the condition, it does not impact a dog’s vision, but they should not be used for breeding purposes just to be on the safe side and should never be bred to dogs diagnosed with Iris Coloboma.

Treatment

For the moment, there is no treatment for Iris Colobomas in dogs. However, any dog known to have the condition should not be used in a breeding programme because it is an hereditary disorder they could pass on to their offspring. With this said, it is not yet known how a dog can pass the condition on to puppies, but what is known is that a higher number of merle dogs seem more predisposed to Irish Colobomas.

Reputable Breeding is Essential

Reputable breeders will always make sure their stud dogs do not suffer from any congenital eye disorders and this includes whether they have Iris Colobomas. Anyone who wishes to share a home with a breed known to be more predisposed to the condition should always ask breeders for certificates from the BVA that show their dogs are free from any hereditary eye disorders. Responsible breeders would also make sure puppies are examined by a veterinary ophthalmologist to ensure they have not been born with the condition. The examination can be carried out on puppies when they are as young as six weeks old.

Living with a Dog with Iris Colobomas

As previously mentioned, any dog can suffer or develop Iris Colobomas with some breeds being more predisposed to inheriting the condition than others. If the coloboma is small, it should not affect a dog's vision at all. However, if they are larger, then more light can enter a dog's eye which causes them to blink and squint which is the only effective way of lessening the amount of light that enters the eye. If a dog has a more severe form of the condition, it's important for them to avoid being subjected to a lot of light which means carefully planning when they are taken for a walk. As previously mentioned, the breeds that are more seriously impacted by the condition are working and herding dogs. Suffering from the condition can make their life very uncomfortable and it often seriously impacts how their work.