By Paul T. Finger, MD
Melanocytoma is a form of nevus that can occur in and behind the iris in the ciliary body. In the image seen below, this melanocytoma has a cobblestone textured surface and feathered margins. Interestingly, it is also causing a small amount of pupillary distortion (correctopia). Bits of iris melanocytoma can break off and settle in the inferior angle. These sedimentary melanocytoma cells can clog the natural drain of the eye (trabecular meshwork), causing increased eye pressure (glaucoma). Melanocytoma tumors can grow, malignant transformation is rare and metastasis is reportable.
Most patients with iris melanocytoma can see a dark spot on their iris, and have no other symptoms. Patients can have pigment dispersion, secondary glaucoma and intraocular inflammation (iritis). Secondary glaucoma can either be asymptomatic, cause one-sided (ipsilateral) headaches and cloudy vision (with halos around lights).
Iris melanocytoma can be diagnosed by clinical examination. The tumor tends to be dark brown to black and the edges feather-shaped. The surface can be cobblestone (bumpy) appearance or smooth.
High-frequency ultrasound is particularly helpful for the diagnosis of iris melanocytoma. This technique is used to evaluate the depth of penetration into the iris and surrounding tissues. It can also be used to monitor for growth. These tumors can extend through the iris and into the ciliary body. Unlike low reflective iris melanomas, they tend to appear bright (highly reflective).
Iris melanocytoma does not usually require treatment. High-quality slit-lamp and gonioscopic photographs should be taken to record the appearance and surface characteristics of the tumor. High-frequency ultrasound should be performed to evaluate its thickness and extension into surrounding structures. These evaluations will be used to monitor for growth. Careful attention should be made to measuring intraocular pressure. Secondary glaucoma can occur due to pigment that clogs the natural drain of the eye (trabecular meshwork). Patients should keep a copy of these baseline tests in case they move to another area or their doctors change.
Should an iris melanocytoma be found to grow, an iris biopsy can be performed to determine if it is benign or malignant. When possible, rapidly growing and malignant iris melanocytomas whould be surgically removed. If resection is not possible, they can be treated with relatively high-dose plaque radiation therapy.
Secondary melanocytomalytic glaucoma can be treated like other glaucomas. It is reasonable to consult with a glaucoma specialist. Strenuous exercise may “shake-up” the intraocular pigment and cause a temporarily increased eye pressure. When this happens, patients may notice headaches or cloudy vision after exercise.
If glaucoma surgery is recommended (e.g. trabeculectomy, stent, valve), a tumor biopsy can ensure that the tumor is not a melanoma.
(See Innovations Section – Finger Iridectomy Technique).