What is an Iris Nevus?
A nevus or freckle is a common growth in or around your eye. A nevus can be in the front of the eye, on the iris, or under the retina, in the part of the eye called the choroid. A nevus is made of cells called melanocytes. Melanocytes produce melanin which is the pigment that colors the hair, skin and eyes. Typically, melanocytes are spread evenly throughout the tissues, but when they clump together they form a nevus.
- An iris nevus is a clump of melanocytes on the iris.
- An iris nevus can be one of two types, circumscribed or diffuse.
- Cogan Reese Syndrome is characterized by a matted iris, iris nevi, and anterior synechiae.
Understanding an Iris Nevus
Iris nevi are the dark spots on the colored part of the eye, the iris. Iris nevi typically appear as hyperpigmented regions of the iris with minimal disruption to the normal iris structure. Iris nevi are larger than iris freckles, and they grow larger and down into a part of the iris called the stroma. There are two types of iris nevi, circumscribed or diffuse. Circumscribed iris nevi are discrete and often nodular. A diffuse iris nevi involves an entire sector or the entire iris. An iris nevus is typically benign, but should be monitored for change. It is estimated that only 8% of iris nevi referred for evaluation at an ocular oncology center transformed into melanoma.
Risk Factors for Malignant Iris Nevus
Several risk factors exist for conversion from benign to malignant including age < 40, the presence of blood (hyphema), located at an inferior clock hour (4:00 to 9:00), diffuse configuration, ectropion uveae, and a feathery tumor margin.
Symptoms of Iris Nevus
An iris nevus typically presents without symptoms unless part of Cogan- Reese Syndrome. Symptoms of Cogan-Reese Syndrome include:
- Blurred vision due to corneal swelling
- Peripheral vision loss if glaucoma is present
Iris Nevus Disorder
Cogan-Reese syndrome is a rare eye disorder characterized by a matted or smudged appearance to the surface of the iris, the development of nodular iris nevi, attachment of portions of the iris to the cornea (anterior synechiae), and/or increased pressure in the eye (glaucoma). This disorder appears most often in young and middle-aged females in one eye, and progresses over time. Cogan-Reese syndrome is one of the iridocorneal endothelial (ICE) syndromes and glaucoma may occur as a secondary disorder.
The secondary glaucoma is believed to be related to a cellular membrane secreted by the abnormal endothelial cells. This membrane covers the trabecular meshwork of the eye’s drainage angle, obstructing aqueous outflow facility and elevating intraocular pressure. In the early disease stage, the angle may appear open although it is covered by this transparent membrane, but with time, contraction of this membrane leads to peripheral anterior synechiae and secondary angle closure glaucoma.
Diagnosing an Iris Nevus
An iris nevus can often be seen in the mirror, but an eye doctor will monitor it for change at a comprehensive eye exam. The doctor may perform gonioscopy to make sure the iris is not affecting the drainage angle of the eye.
Iris Nevus Treatment
No treatment is typically needed for a benign iris nevus. If Cogan-Reese syndrome is diagnosed, the secondary glaucoma must be managed or it will lead to vision loss. Cogan-Reese syndrome is treated with eye drops to lower the intraocular pressure and reduce swelling (edema). Mild cases of corneal edema are managed with soft contact lenses and hypertonic saline solutions. Aqueous suppressants, including beta blockers, alpha-2 agonists and carbonic anhydrase inhibitors are used to treat the secondary glaucoma. Prostaglandin analogues may be beneficial for some patients. Surgical intervention for glaucoma is often required in a high percentage of patients with ICE syndrome. Trabeculectomy is most often performed with variable success.