Degeneration of the Iris in the Eye in Dogs

Iris Atrophy in Dogs

The degeneration of the iris -- the colored part of the eye -- is referred to as iris atrophy. This can be as a result of normal aging or, if due to a secondary type, because of chronic inflammation or high intraocular pressure, which is often associated with glaucoma. Iris atrophy can affect any breed, but appears to be more common in small breed dogs, such as chihuahuas, miniature poodles, and miniature schnauzers.

Symptoms and Types

Vision is not usually affected by iris atrophy, but there may be some sensitivity to light. Other typical symptoms associated with this of disorder include:

• Incomplete pupillary light reflex, accompanied by a normal menace response (the reflex to close the eyes when a finger is stabbed toward the eye)
• Unilateral — may note unequal pupil sizes (anisocoria)
• Irregular, scalloped edge to the pupillary margin
• Thin or absent areas of the iris on transillumination
• Strands of iris occasionally remain, spanning across portions of the pupil
• Holes within the iris stroma — black spots that may resemble additional pupils
• Swelling (edema) of the cornea

Causes

• Normal aging
• Uveitis (inflammation of the uvea portion of the eye)
• Glaucoma

Diagnosis

Your veterinarian will perform a thorough physical and ophthalmological exam on your dog. The initial goal will be to differentiate iris atrophy from congenital iris anomalies, as there are a variety of other eye issues that can be the cause of the symptoms, such as iris aplasia (failure of the iris to develop normally), iris hypoplasia (underdevelopment or incomplete development of the iris), iris coloboma (a complete, full-thickness area of lack of development of all layers of the iris), and polycoria (when more than one pupil is present in a single iris within the animal's eye, each with the apparent ability to constrict).