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My Dog Has A Dark Area in the Eye's Iris

My Dog Has A Dark Area in the Eye's Iris

Eyes are the windows of the soul, but when it comes to diagnostics, the eyes can also be windows of a dog's over all eye health. Looking into a dog's eyes routinely, is a good way to recognize early signs of trouble such as noticing a dark area in the dog's iris, the colored portion of a dog's eyes. There are several eye conditions that can cause dark areas in the dog's colored part of the eye, some may be benign others may be more serious, but only a veterinarian can really determine the exact cause. Sometimes complicated cases are referred to a the specialists in the field: board-certified veterinary ophthalmologists.

The Help of Light

Being in a room with good lighting can help you better see the area so to check for darkened areas in the dog's iris. Try to stay by a window and use a treat kept at eye level to get your dog to look in your direction. Praise and reward with the treats as you get a better look into your dog's eyes.

Shining a light in the dog's eye may also help determine if the dog's vision is affected, explains veterinarian Dr. Gary. Simply, stay in a dark room and shine a light in the dog's eye. In a dog with normal vision, the pupil gets smaller when the light is shined, and gets bigger when the light is no longer shined.


Iris Cyst in Dog

Presence of an Iris Cyst

Also known as uveal cyst, an iris cyst in dogs is a hollow structure that is often found attached to the dog's iris.

It's composed of a layer of tissue that is filled with fluid. It often arises secondary to some sort of inflammation to the eye such as the presence of glaucoma.

While an iris cyst can occur in different breeds of dogs, they are most commonly found in Golden and Labrador retrievers and Boston terriers.

Typically, when a light is shined towards an iris cyst in a dark room, it "transilluminates"meaning that the light goes through it, just as light goes through people's fingers, revealing a red glow.

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Presence of Iris Melanocytoma

This is a form of benign tumor affecting the dog's eye and it quite common. It is basically, the benign, non-spreading version of canine melanoma affecting the eye.

According to VCA Animal Hospitals, the most common melanomas of the eye tend to originate from the dog's iris and are usually benign. These tumors arise from the pigmented cells (melanocytes) that are found in the dog's iris and which are responsible for giving color to the eye. Iris melanocytomas tend to affect one eye only.

Veterinary ophthalmologists may recommend eye removal should the eye become unsightly and unresponsive to treatment. In the early stages, this tumor may be removed through lase or cryotherapy, but these tend to re-occur, explains Andrew Geller, a veterinary ophthalmologist.

Did you know? Limbal melanocytomas are solid masses that arise from the pigmented ring (limbal ring) found around the dog's eye.


Presence of Iris Malignant Melanoma

A malignant melanoma affecting the eye means that it is prone to spreading (metastasizing). Sometimes these pigmented masses on the iris may be slightly raised above the surface. The presence of a mass on the iris may be the only symptom. These masses often present as heavily pigmented, but can also presnt as tan or white. When allowed to grow, the mass may distort the pupil and even cause secondary glaucoma or sometimes uveitits, according to Vetfolio.

What to Do?

Because there are several conditions affecting a dog's eye that can cause dark areas in the dog's iris, it is best to see a vet to attain proper diagnosis. At times, a microscopic examination of the dog's ocular tissue is all that's needed and this can be obtained through aspirates, biopsies and excisions of the tissue. These samples are then sent out for microscopic examination by a pathologist who can provide in most cases, accurate diagnosis and prognosis.


Veterinary Ocular Pathology: A Comparative Reviewm, By Richard R. Dubielzig, Kerry L. Ketring, Gillian J McLellan, Daniel M. Albert, Saunders Ltd.; 1 edition (4 May 2010)

Photo Credits:

  • Iris cysts, by Joel Mills - Own work, Multiple brown iris cysts seen against the blue iris of a Boston Terrier. The topmost object is clearly hollow, identifying it as a cyst CC BY-SA 3.0

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