Malignant Melanoma of the Iris

Symptoms

often asymptomatic; frequently detected during routine dilated examination

blurred vision or metamorphopsia if the tumor causes exudative detachment

floaters associated with vitreous hemorrhage or tumor-induced uveitis

acquired heterochromia (iris darkening) in diffuse variants

Clinical Findings

Clinical hallmarks

• unilateral pigmented (rarely amelanotic) mass with prominent intrinsic feeder vessels
• predilection for the inferior iris and patients with light iris color
• ectropion uveae: outward rotation of the pupillary margin (classic tractional sign)
• corectopia: distorted pupil pulled toward the tumor site
• sector cataract: focal lens opacity at the point of tumor-lens contact

Secondary complications

• spontaneous hyphema (bleeding into the anterior chamber)
• secondary glaucoma: tumor invasion of the angle or pigment seeding

Imaging & diagnostics

• ultrasound biomicroscopy (ubm): mandatory to measure thickness and check ciliary body extension
• transillumination: solid melanoma blocks light (distinguishes it from a clear iris cyst)
• as-oct: high-resolution imaging for smaller, anterior lesions

Etiology

Pathogenesis

• arises from uveal melanocytes; most common primary intraocular malignancy in adults
• risk factors: ocular melanocytosis (nevus of ota), bap1 mutation, and light skin/iris

Cytogenetics

• monosomy 3 and gain of 8q are strong predictors of metastatic spread (liver)

Red Flags

new or growing pigmented lesion with associated ectropion uveae

unilateral elevated iop with a darker iris (suspect diffuse iris melanoma)

bony erosion or extrascleral extension on imaging

systemic symptoms like weight loss or hepatomegaly

Investigations

Ocular evaluation

• detailed slit-lamp exam with gonioscopy to evaluate angle invasion
• indirect ophthalmoscopy to rule out ciliary body or choroidal involvement
• ubm: to determine basal diameter and apical thickness

Systemic staging

• lfts and ldh; liver mri or ultrasound to screen for metastasis
• fine-needle aspiration biopsy (fnab) for cytogenetics (monosomy 3)

Treatment

Local control

• plaque brachytherapy (i-125 or ru-106) for most circumscribed tumors
• proton beam irradiation for tumors involving the angle
• surgical resection (iridocyclectomy) for localized iris/ciliary body lesions
• enucleation for diffuse melanoma or blind, painful eyes with glaucoma

Systemic

• oncology co-management for high-risk patients

Clinical Pearl

A choroidal melanoma does not spare the life of the patient if it spares the eye — the #1 prognostic factor is tumor cytogenetics (class 2, monosomy 3), not size or globe-conservation status.

Differential Diagnosis

• iris nevus (stable, no vessels, no ectropion uveae)
• iris cyst (clear on ubm, transilluminates)
• iris metastasis (rapid growth, amelanotic, pseudohypopyon)
• lisch nodules (bilateral, associated with neurofibromatosis type 1)
• fuchs heterochromic iridocyclitis

Related Oncology Conditions

• Conjunctival Tumors
• Orbital Tumors