Dog Dark Eye Pigmentation on MedicineNet

My Dog Has a Dark Spot in One Eye

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Except in cases of true albinism, dogs' irises - the colored part of the eye - range in color from pale blue to dark brown. However, variations in development before a puppy is born can cause color variations within the iris resulting in multiple colors within one eye. Normal variations usually appear as wedge-shaped, streaks, or bursts of a different color within an iris, such as a streak of brown in a blue eye. Abnormal pigment can often be easily identified and is not always dangerous.

What to Look For

You likely don't have to get too close to your dog to see an unusual spot in one or both of her eyes. Simply take a look at both of her eyes and note where the pigment is and what shape it is.

Next, you want to see if the pigment is fixed or moves around. Observe your dog first while she is standing looking directly at you. Note the location of the area of pigment. Next, place your dog on her side and again note the position of the pigment. Finally, place your dog on her back with her head on the ground and her throat facing the sky and examine the placement of the pigment. If the pigmented area is fixed, it will remain in the same location regardless of your dog's position. If it is a mass of some sort, its point of origin will remain fixed but its body may shift with your dog's position. (Think of a bean bag stapled to the face of a clock. The bag will tend to droop with the pull of gravity, toward the number six on the dial. If you then rotated the clock face so that another number was facing downward, the bag would droop toward it.)

What to Do

Now that you've gotten a good look at what's going on, ask yourself the following questions:

How old is your dog? If your dog is a puppy or if she is an adult that you just purchased or adopted, the pigment you are noticing may be a perfectly normal congenital trait. However, if your dog is an adult and this is a new development, it is more likely cause for concern.
Is the pigment confined to the iris, or colored part of the eye, or is it elsewhere within the globe? Normal pigmentation within the eye is always associated with the iris. If the pigment you are questioning appears to be separate from or only partially within the iris, it is worth investigating with your vet. If the pigment is entirely within the iris and your dog seems unaffected by it, keep a close watch on it either until changes in size, shape, or color are noticed or until your dog's next veterinary visit, whichever comes first.
Is the pigment well-defined with clear, crisp edges or are the boundaries amorphous, fading into the surrounding, colored part of the iris? While rough, poorly defined edges to an area of pigment are more worrisome than those with clear outlines, not all such lesions are dangerous. Many pigments in the iris are simply areas of different color, similar to freckles on the skin, called iris nevi. Some iris nevi remain the same throughout a dog's life, never causing a problem. However, others can become dangerous, and eventually be identified as melanocytomas or malignant melanomas.

If the edges are rough, have it seen. If they are crisp and clean, monitor them closely for changes or until your next veterinary appointment.

Is the pigment the only problem with your dog's eye? Dogs with tumors in their eyes will often have other symptoms, such as glaucoma or inflammation of the eye, which is called chronic uveitis. If your dog seems to have more than one symptom relating to his eye, it is always best to have him seen by a veterinary ophthalmologist who has the instruments to make more precise, accurate diagnoses than a general practitioner.
Is the pigment fixed or does it move within the eye? If it is an iridal cyst, it may be free floating, in which case it will fall to the bottom of your dog's eye regardless of his position. These are benign and only require intervention if they become large enough, numerous enough, or fixed in a position to obstruct vision.