Total and partial (one eye) blindness is very common among double merles. Some dogs will be born completely blind, or even without eyes.
Most double merles will suffer from some sort of vision impairment. There are a myriad of different eye abnormalities seen among double merles. Dogs can suffer from one, or in many cases, several. Vision impairment can range from being very slight to complete blindness. Below you will see photos of different eye abnormalities. In many of the eyes there is more than one abnormality present. Any of these abnormalities or blindness will be present at birth, with the exception of cataracts.
Calypso, a double merle Great Dane, was born blind. As she grew into an adult, the small eye that was present in each socket needed to be removed.
Keeley, a Catahoula mix, was born with no vision in her left eye and only about 5% in her right eye.
Forrest, a double merle Australian Shepherd, was born blind.
Moo is blind in this eye (left) and has abnormalities in her other eye.
This is a very common condition in the eyes of double merles. The pupil will be shaped with spiked, jagged, or irregular edges. This does not allow the pupil to react normally to light and can cause a light sensitivity for the dog.
Microphthalmia is one of the most common eye defects seen in double merles. Microphthalmia in layman's term means, "small eye." The severity of this abnormality can vary greatly. Dogs with this condition can have nearly normal looking eyes. However, the smaller the eyes, the more you will see of the third eyelid. This can cause a problem with the dogs vision if the third eyelid is covering too much of the dogs eye. This eye defect can be very severe and get to the point where it appears the dog has no eyes (anophthamia).
Jessie, a double merle Australian Shepherd, has severe micophthalmia in this eye. You can see how small it is and that it's barely there.
Ralph, a double merle Australian Shepherd, has microphthalmia in this eye. You can see the edge of the very small eye and how the third eye lid covers it.
Corectopia is a condition where the pupil will be subluxated or "dropped". The pupil will not be in the center of the dog's iris as it normally is. This usually has little effect on the dogs vision unless it is paired with other eye abnormalities.
Cataracts are also found in the eyes of many double merles. These cannot be seen by the naked eye or in a photograph. Cataracts can be incipient or incomplete where it is not fully formed and causes little issue with sight. Any cataract should be monitored as it can change and potentially cause vision loss.
Not all double merles are faced with eye abnormalities, but a large majority of them are. If you own a double merle, it is highly recommended that you see a veterinary ophthalmologist at least once. Even if your dogs eye appears to look normal, there could be abnormalities that you cannot visualize.