Iris Cysts in Cats

Iris cysts must be properly diagnosed in order to be differentiated from an iris melanoma, which is a type of tumor that can be dangerous to the eye. Proper diagnosis is essential in saving the cat's vision and prevent glaucoma from occurring.

The iris of the cat's eye provides most of the color of the eye and regulates the amount of light that enters the eye in order for the cat to see properly. Iris cysts, which are also known as ciliary body cysts, uveal cysts, or iridociliary cysts, are typically small, fluid-filled structures with a hollow center that develop on the surface of the eye. Though they sometimes can float freely in the anterior chamber, the cysts most often attach to the pupillary margin, the boundary where the iris and the pupil meet. Though the cysts are usually benign and pose no medical risks, they can interfere with eye function and vision. Rarely, iris cysts can cause complications, such as glaucoma, to develop. Siamese cats are more likely to develop iris cysts than other breeds of cats.

The main symptom of iris cysts is visual evidence of the cyst. The cysts are semi-transparent due to their hollow core, are circular or ovular in shape, and can vary in size. There may be more than one cyst present in one or both eyes. Small cysts are normally only found during routine exams. Larger cysts are typically noticeable by the cat owner or by the symptoms of loss of vision, such as running into walls or difficulty in batting small objects.

There are two types of iris cysts: congenital and acquired.

Congenital iris cysts are present at birth. They are caused by an abnormality in the development of the eye during fetal development. The cause of acquired iris cysts is often not known; however, eye inflammation (uveitis) and eye trauma can both contribute to the cysts forming.

The veterinarian will need to know the cat's health history, when the cysts first became noticeable and if any visual difficulties are present. The veterinarian will diagnose the cyst with an ocular exam. This will be done by carefully looking into the cat's eyes. The veterinarian will direct light at the iris cyst. True iris cysts will illuminate due to their hollow nature, differentiating them from iris melanomas, which will not illuminate due to the fluid inside of the neoplasms. 

Because iris cysts can contribute to the development of glaucoma, the veterinarian may also look for evidence of glaucoma in the cat's eyes. A tonometry test will be performed to measure the amount of pressure in the cat's eyes to determine if glaucoma has developed.

Aspiration

If the cysts are causing visual impairment in the cat, the veterinarian will need to remove the cysts. One option is a procedure known as aspiration. The cat will be given a tranquilizer in order to relax it while the procedure takes place. The veterinarian or veterinary optometrist will insert a fine needle into the cyst, slowly drawing out the fluid inside of the structure. Once the fluid has been removed, the structure will collapse and eventually dissolve. This procedure poses the risk of infection and of damage to the surrounding eye tissue.

Noninvasive Laser-Induced Deflation

The veterinarian may also choose to deflate the cysts using a noninvasive laser. This is the preferable method as it poses less of a risk of infection and damage to the surrounding tissue. The procedure takes approximately 10 minutes. A head-mounted laser beam will be focused on the iris cyst using a handheld lens. The lens allows the laser to be concentrated and targeted directly on the cyst, without any danger to the surrounding eye tissue. The laser will coagulate the fluid inside of the cyst, causing the structure to deflate and become re-absorbed by the body.

Glaucoma Treatment

If glaucoma was found as a result of the iris cyst, medications will be prescribed in order to prevent fluids from being produced in the eye and to encourage drainage. Surgery may also be necessary in order to prevent total or partial blindness from occurring.

If the veterinarian determined that the cyst was small enough to not need prompt treatment, the cat will need to follow up with the veterinarian to check the size and growth of the cyst. Cats who received aspiration or laser treatment will also have to follow up to determine the effectiveness of the procedures and if any additional treatment is necessary. Cats with glaucoma will also need to follow up in order for the veterinarian to determine if any changes in the prescriptions need to occur or if surgery needs to take place in order to save the cat's vision.