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Disease Entity

Iris nevus is a benign melanocytic proliferation of the iris stroma characterized by a localized accumulation of melanocytes. It is considered part of the spectrum of uveal melanocytic lesions.

Epidemiology

Iris nevi occur in less than 5% of the population and are the most common melanocytic tumors of the iris in all ages, accounting for approximately 61% of all melanocytic iris tumors in the series reported by Shields et al. (2012). They are typically diagnosed in early to middle adulthood, the mean patient age at presentation being 51 years in a cohort of iris nevus by Shields et al. (2013). They are more frequently observed in females, Caucasian individuals with light iris pigmentation.

Etiology

Iris nevi arise from benign proliferation of melanocytes within the iris stroma. The precise molecular mechanisms remain incompletely understood. Similar to other melanocytic lesions, ultraviolet light exposure and genetic susceptibility may contribute to lesion development. Cells may be spindle-shaped or mixed spindle and epithelioid. Cytologic atypia is minimal or absent, mitotic activity is rare, and invasion into adjacent structures is not present.

Diagnosis

Diagnosis is primarily clinical and based on slit-lamp biomicroscopy.

Typical iris nevi are:

Well-circumscribed

Flat or minimally elevated
Pigmented (brown) lesions
Usually less than 3 mm in diameter
Often associated with localized iris stromal distortion

Some lesions may be amelanotic.

Symptoms

Most patients are asymptomatic. Symptomatic lesions may produce visual changes, glare, photophobia and ocular pain due to elevated intraocular pressure.

Diagnostic Procedures

Serial slit-lamp photography is essential for documenting lesion stability or growth.

Gonioscopy is useful to evaluate trabecular involvement.

Ultrasound Biomicroscopy (UBM) is particularly valuable for assessing:

Tumor thickness
Ciliary body extension
Angle involvement
Internal reflectivity

Anterior Segment Optical Coherence Tomography (AS-OCT) may help characterize smaller superficial lesions but is limited in heavily pigmented tumors.

Fine Needle Aspiration Biopsy (FNAB) is rarely required. FNAB may be considered in diagnostically uncertain lesions or when molecular characterization is necessary.

Differential Diagnosis

Differential diagnosis includes:

Iris melanoma
Iris freckle
Lisch nodules
Iris melanocytoma
Adenoma of the iris pigment epithelium
Foreign body
Iris cyst
Metastatic lesion
Granulomatous nodules
Essential iris atrophy

Management

Most iris nevi are managed conservatively with periodic observation.

Suggested follow-up intervals:

Every 3–6 months initially for suspicious lesions
Annually for stable lesions

Complications

Potential complications include:

Secondary glaucoma
Hyphema
Cataract formation
Cosmetic pupil distortion
Malignant transformation

Prognosis

Most lesions remain stable over time; however, a small subset demonstrates growth and transformation into iris melanoma. In longitudinal cohort studies, the estimated risk of transformation of iris nevus into melanoma has been reported at approximately:

<1% at 1 year
3–4% at 5 years
8% at 15 years
10–11% at 20 years

Clinical features associated with increased risk of transformation to melanoma include:

Younger age
Documented tumor growth
Inferior iris location
Diffuse configuration
Presence of ectropion uveae
Hyphema
Intrinsic tumor vascularity
Feathery or indistinct margins
Seeding into the angle
Secondary glaucoma

The mnemonic “ABCDEF” has been proposed to aid recognition of suspicious lesions:

Age younger than 40 years
Blood (hyphema)
Clock hour inferiorly
Diffuse configuration
Ectropion uveae
Feathery margins

References

Shields CL, Kaliki S, Hutchinson A, et al. Iris nevus growth into melanoma: analysis of 1611 consecutive eyes: the ABCDEF guide. Ophthalmology. 2013;120(4):766-772.
Shields JA, Shields CL. Intraocular Tumors: An Atlas and Textbook. 3rd ed. Philadelphia, PA: Wolters Kluwer; 2016.
Conway RM, Chua WC, Qureshi C, Billson FA. Primary iris melanoma: diagnostic features and outcome. Ophthalmology. 2001;108(9):1727-1732.
Harbour JW. The genetics of uveal melanoma: an emerging framework for targeted therapy. Pigment Cell Melanoma Res. 2012;25(2):171-181.
Finger PT. Radiation therapy for choroidal melanoma. Surv Ophthalmol. 1997;42(3):215-232.

Iris Nevus

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