Uveal Cysts

The term cyst refers to a fluid-filled structure lined by epithelial cells, similar to a water balloon.  When these occur in the eye, they most often originate from the vascular tissues of the eye, called the uveal tract.  The uveal tract includes the iris, the ciliary body, and the choroid.   The iris is the easiest uveal structure to see, as it is the colored (brown, blue, golden, green, etc.) muscular tissue in the front of the eye that creates the black pupil.  A cyst from the iris often appears dark or sometimes transparent, depending on species and how the light catches the cyst.  They can be attached or free-floating within the fluid of the eye.

What causes these cysts?

We do not exactly know what causes the cysts to form.  There is likely a genetic component since they occur more frequently in certain dog breeds such as Boston Terriers, Golden Retrievers and Labrador Retrievers.  While some cysts may result from abnormal contact between layers of the uveal epithelium, others are believed to be caused by inflammation inside the eye.

When do we worry about cysts?

Cysts often do not cause a problem for veterinary patients, but if they do become a problem, your doctor may discuss options for cyst removal, such as surgical aspiration or laser treatment.   Our primary concern with cysts, in most dogs, is that they can interfere with vision.  In some dogs and in horses, the cysts can cause behavior changes that are believed to be due to the changes to vision.

We worry more about cysts in specific dog breeds, including Golden Retrievers, American Bulldogs, and Great Danes, because there has been a strong link between the presence of cysts and the development of glaucoma, which is a vision-threatening, painful condition.  If you have one of these breeds, medical treatment and/or surgical treatment may be recommended.

How do we know these are not cancer?

It is very important to distinguish uveal cysts from melanoma, which is the most common intraocular cancer in veterinary patients.  In general, we can distinguish between the two because cysts will allow light to pass through them (called transillumination) and melanomas will not.  Sometimes, particularly in cats and horses, cysts do not transilluminate and may require an ocular ultrasound to determine whether they are fluid-filled (cysts) or solid (possible cancer).