Degeneration of the Iris in the Eye in Cats

Degeneration of the iris in the eye, also called iris atrophy, is a slow and progressive, yet rare, condition that occurs as a cat ages. The cat eventually develops an inability to properly block out bright light. However, the condition can be linked to more serious ocular diseases that stem from a systemic infection. Iris atrophy is largely considered benign and usually affects just one eye. The prognosis is generally good and no vision loss should occur if diagnosed and treated quickly.

The iris is the round, pigmented membrane that surrounds the pupil. It involves the stroma (the white part of the eye) as well as a sphincter muscle that contracts or expands the pupil to regulate the amount of incoming light. Degeneration, or atrophy, of the iris, though rare in cats, is commonly due to simple aging. However, it may also be due to inflammation of the uvea (uveitis), chronic intraocular pressure (glaucoma), or as a result of a traumatic injury. Severe cases will result in an inability to block out bright lights. If changes of the iris happen suddenly it is considered an emergency situation as your cat’s vision could be permanently affected if not properly treated.

Symptoms of degeneration of the iris commonly include:

• Unequal pupil sizes (anisocoria)
• Irregular edges around the pupil
• Thin or absent areas when a light is shined on the eye
• Strands of pigmentation spanning across portions of the pupil that look like lace
• Black spots or redness on the stroma 
• Swelling
• Pain or discomfort
• Cloudy or bluish colored cornea
• Unusual discharge
• Squinting or rubbing of the eye

Types

Even though degeneration of the iris is usually harmless, there are two types of more serious conditions.

Iris Melanoma

This is the most common primary intraocular tumor in cats. Signs of melanoma include progressive increase in iris pigmentation and the onset of secondary glaucoma, which is usually associated with a systemic infection. Early detection is critical as these tumors metastasize early and aggressively. 

Uveitis

This condition is an inflammation of the uveal tract, which includes the iris, ciliary body, choroid, and sometimes the retina. It is often associated with a systemic disease or severe trauma and can clinically present itself like conjunctivitis. Anti-inflammatory medication and modern laboratory techniques are making control of the condition more efficient. However, the disease is not always controllable and will usually require lifetime treatment.

The ability of your veterinarian to differentiate between iris melanoma and uveitis is difficult but essential for correct treatment.

Degeneration of the iris is generally a rare condition that could be caused by several conditions, including:

• Aging
• Intraocular pressure (glaucoma)
• Inflammation of the uvea
• Feline immunodeficiency virus (FIV)
• Feline herpesvirus-1 (FeHV-1)
• Toxoplasmosis (infection of a parasite that can be found in undercooked meat)
• Feline leukemia virus (FeLV)
• General fungal or bacterial infection
• Hypertension
• Melanoma
• Lymphosarcoma
• Hyperpigmentation
• Traumatic injury
• Cranial nerve abnormalities

Your veterinarian will initially want to conduct an overall physical examination, take a medical history, and perform an eye exam in order to make a definitive diagnosis between atrophy or another ocular disorder.

The diagnosis process may also include a full blood count, heartworm test, fluorescein stain test, a test on the fluid coming from the eye, and any testing to determine FeLV, FIV, or any kind of infection.

If the cause for the degeneration cannot be determined, you will be referred to a veterinary ophthalmologist.

Often iris atrophy is due to simple aging and no treatment will be given. If during diagnostic testing, however, an infectious disease is found to be the cause of atrophy or of any form of degeneration, treatment will be directed at the underlying disease in order to preserve your cat’s vision and to prevent any possibility of blindness. 

Treatment for an underlying condition may include any topical, oral, or systemic medications such as anti-inflammatories, antiviral or antibacterial therapies, and antibiotics. Follow-up examinations will be necessary. A referral to a board-certified veterinary ophthalmologist may also be recommended. 

Detection of possible glaucoma (intraocular pressure) is highly important and the condition will be aggressively controlled if found. If left untreated, the eye will become very painful and blindness will develop, sometimes resulting in having to remove the eye. It is more common that your cat will recover some of its vision, however.

If the iris atrophy is associated with a systemic infection, the prognosis for full recovery depends on your cat’s response to treatment. In some cases, your cat may require long-term medication to control the underlying cause.

More likely, the iris atrophy is just a part of natural aging and is benign. However, there is a chance the condition could become progressively worse over time. In the meantime, refraining from exposure to bright light or sunlight is highly recommended.