eMedicine Specialties > Ophthalmology > Iris & Ciliary Body

Melanoma, Iris

Author: Nadia K Waheed, MD, Consulting Staff, Department of Vitreoretinal Disease, Cole Eye Institute/Cleveland Clinic Foundation
Coauthor(s): C Stephen Foster, MD, FACS, FACR, FAAO, Clinical Professor of Ophthalmology, Harvard Medical School; Consulting Staff, Department of Ophthalmology, Massachusetts Eye and Ear Infirmary; Founder and President, Ocular Immunology and Uveitis Foundation, Massachusetts Eye Research and Surgery Institution
Contributor Information and Disclosures

Updated: Jul 11, 2008

Introduction

Background

Iris nevi and melanomas are the most common primary tumors of the iris, with an incidence ranging from 50-70% of all iris tumors; of these, 10-24% may be melanomas. Melanomas arise from malignant proliferation of the neuroectodermally derived iris stromal melanocytes, which replaces the normal iris stromal architecture. Considerable controversy exists regarding the histopathologic classification and the malignant potential of iris melanomas.

Pathophysiology

Most iris melanomas are believed to arise from active growth in preexisting nevi. Epidemiologic studies suggest that sunlight exposure plays a role in the pathogenesis of iris melanomas.

Secondary glaucoma in iris melanomas may result from several different mechanisms, to include the following: invasion of malignant cells into the trabecular meshwork, decreased aqueous outflow due to pigment-ingesting macrophages blocking the angle, angle closure, or neovascularization.

Frequency

International

Although iris melanomas are the most frequent primary malignancy of the iris, they form only a small proportion (3-13%) of all uveal melanomas. Clinical and histopathologic studies show that only 13-25% of all suspected iris melanomas actually meet the criteria for melanomas.

Mortality/Morbidity

Most primary tumors of the iris are benign. Iris melanomas are considered to be much less aggressive than melanomas of the choroid and the ciliary body.

• The mortality rate from iris melanomas varies from 0-11% depending on the presence or the absence of metastases and ciliary body involvement.
• Metastases occur in 2-10% of all iris melanomas; a higher rate is observed in cases of ciliary body involvement.

Race

Iris melanomas are more common in whites and in people with light-colored irides than in people of Asian or African descent.

Sex

No known sexual predilection exists.

Age

The average age at diagnosis is 40-50 years; however, persons of any age can be affected.

Clinical

History

• Many patients provide a history of a nevus existing since childhood that has suddenly undergone rapid growth.
• Patients may present because of cosmetic concerns.
• Patients may experience pain due to increased intraocular pressure.

Physical

• Iris melanomas may be circumscribed or diffuse. 
  • Circumscribed melanomas have a nodular shape and are more common in the inferior iris. They can grow anteriorly into the anterior chamber or posteriorly into the posterior chamber, usually being limited by the lens and giving a “lion’s paw” appearance on ultrasound biomicroscopy (UBM).
  • Melanomas involving the anterior chamber angle can also invade the ciliary body. Thus, in these tumors, gonioscopy and UBM of the ciliary body is critical.
  • Diffuse melanomas cause acquired heterochromia and also have associated glaucoma. This glaucoma tends to respond poorly to medical management and causes severe disc cupping and functional loss. Diffuse melanomas also tend to be of the epithelioid cell type, with a higher risk of metastasis than circumscribed melanomas.
  • Ring melanomas involve more than two thirds of the angle and have associated glaucoma.
  • Tapioca melanomas are multifocal nodules projecting into the anterior chamber that may be associated with glaucoma.
• According to Shields, criteria for a clinical diagnosis of melanoma are as follows:¹
  • The size is greater than 3 mm in diameter and 1 mm in thickness.
  • It replaces the stroma of the iris.
  • Three of the following 5 features are present: photographic documentation of growth, secondary glaucoma, secondary cataract, prominent vascularity, and/or ectropion irides.
• Ciliary body involvement is associated with a higher incidence of malignancy.
• Medial location and pigment dispersion onto the iris or the angle structures are associated with tumor growth.
• Many of these traditional signs of malignancy are being challenged by new studies. However, even though many of these features may be more common in benign tumors than in malignant melanomas, their presence should alert the ophthalmologist to closely monitor the lesion.
• A thorough ophthalmologic examination, including transillumination and indirect examination with scleral depression, is essential to differentiate among iris cysts, primary iris tumors, and primary ciliary body melanomas.
• Gonioscopy and UBM of the entire ciliary body must also be performed to rule out involvement prior to any therapeutic decision making.

Causes

• Sunlight exposure is a known risk factor.
• Chromosomal mutations may be involved.

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