Iris Nevus
A benign, discrete melanocytic lesion of the iris stroma, found in approximately 6% of the general population. Most are stable and clinically insignificant, but all require slit-lamp photographic documentation and serial monitoring to exclude rare malignant transformation to iris melanoma. Accurate characterisation and differentiation from iris melanoma is the primary clinical imperative.
Last updated: March 2026
Panel A — Anterior View (Slit-Lamp)
Panel B — Cross-Section (Nevus vs Melanoma — Key Differentiators)
Panel A: Anterior view of a small, flat, well-defined iris nevus in the inferior-temporal quadrant with undisturbed adjacent crypts and round pupil — key benign features. Panel B: Cross-section comparing benign nevus (flat, anterior stroma only, intact posterior layers) with suspicious melanoma features (dome-shaped, full-thickness, intrinsic vessels, angle seeding). Shields ABCDEF mnemonic guides risk assessment.
An iris nevus is a benign, discrete, melanocytic lesion of the iris stroma comprising the most common iris tumour seen in clinical practice. Prevalence is approximately 6% in the general population. Nevi typically appear in childhood or early adulthood, presenting as a small (<3 mm base, <1 mm height), flat or minimally elevated, brown-to-dark-brown, well-defined pigmented lesion, most commonly in the inferior iris quadrants. They are generally single but can be multiple. Most iris nevi are clinically insignificant and require only periodic surveillance; however, their primary clinical importance lies in differentiating them from iris melanoma, which shares a similar melanocytic origin but carries the risk of metastatic disease.
The distinction between iris freckle (a very common, purely superficial melanocytic deposit with no stromal involvement), iris nevus (stromal involvement, discrete, lesion architecture), iris melanocytoma (intensely jet-black, morphologically distinct, large, can seed the TM), and iris melanoma (growth, vascularity, sentinel vessels, TM seeding) forms the basis of clinical decision-making. At the first clinical encounter, all iris lesions must be documented photographically with measurement of their clock-hour position, maximum basal diameter, and height. Serial monitoring with photographic comparison is the cornerstone of management for stable lesions.
Benign Melanocytic Proliferation
Iris nevi arise from a localised, benign proliferation of melanocytes within the iris stroma. Unlike posterior uveal melanoma, iris nevi have no confirmed oncogenic driver mutations (e.g., no GNAQ/GNA11 hotspot mutations typically associated with uveal melanoma). The cells retain normal cytological morphology — regular nuclei, normal cell-to-cell relationships, and no invasion of surrounding tissues.
Genetic Predisposition Factors
There is no single gene identified as the primary driver for iris nevi. Risk factors include light iris colour, fair skin, personal or family history of dysplastic nevi (atypical mole syndrome), and oculodermal melanocytosis (naevus of Ota). In the context of naevus of Ota, uveal melanocytes (including those of the iris) are abnormally increased in number from birth, representing a hamartomatous proliferation rather than a de novo acquired lesion.
UV Radiation
Ultraviolet (UV) radiation may influence melanocytic activity in the iris, but the evidence is less compelling than for cutaneous nevi. Iris melanocytes are largely shielded from direct UV exposure by the cornea and aqueous humour, which filter UV wavelengths. The relationship between UV exposure and iris nevus development is less established than for posterior uveal melanoma.
- Localised melanocyte accumulation: A discrete population of iris stromal melanocytes undergoes localised benign proliferation, accumulating within the stroma without breaching surrounding tissue boundaries. The basement membrane and normal extracellular matrix architecture are maintained.
- Retention of normal melanocyte morphology: Benign nevus cells are cytologically identical to normal iris melanocytes: regular nuclei, adequate cytoplasm, no significant pleomorphism, no mitotic figures. This distinguishes them from malignant melanoma cells at histopathological examination.
- Absence of angiogenesis: Benign iris nevi do not generate new intrinsic blood vessels (neovascularisation) within the lesion. The absence of intrinsic vascularity on fluorescein angiography is a key feature distinguishing benign nevi from melanoma (which often generates sentinel feeder vessels).
- No trabecular meshwork seeding: Unlike iris melanoma (which can shed melanocytic cells into the anterior chamber to seed the trabecular meshwork, causing melanomalytic glaucoma), benign iris nevi do not shed cells into the aqueous humour in significant quantities. TM seeding and resultant glaucoma would be a warning sign of malignant transformation.
- Malignant transformation mechanism (rare): If transformation to iris melanoma occurs, it likely follows sequential acquisition of somatic mutations (including possible GNAQ/GNA11 pathway involvement) that confer growth advantage, loss of contact inhibition, and neovascularisation. The estimated transformation rate is <1% lifetime for iris nevi — substantially lower than for posterior uveal nevi (~1:8,000 per year).
Iris melanocytic lesions are classified by architecture, morphology, and clinical behaviour:
| Lesion Type | Architecture | Colour | Behaviour | Stromal Involvement |
|---|---|---|---|---|
| Iris freckle | Flat, superficial, multiple | Light to medium brown | Benign; no malignant potential | No (surface only) |
| Iris nevus | Flat to slightly elevated; <3 mm base; well-defined | Medium to dark brown | Benign; <1% malignant transformation risk | Yes (stromal) |
| Iris melanocytoma | Elevated, irregular surface; can be large | Intensely jet-black (almost black) | Benign but can seed TM; rare malignant change | Yes (deep stromal) |
| Diffuse iris melanosis | Diffuse darkening of one iris; no discrete lesion | Diffuse brown darkening | Benign variant; monitor for melanoma if progressive | Yes (diffuse) |
| Iris melanoma | Elevated (>1 mm), irregular, with feeder vessels | Variable (brown to amelanotic) | Malignant; documented growth; TM seeding; glaucoma | Yes (invasive) |
- Light iris colour (blue, grey, hazel): Lower melanocyte density in light irides; paradoxically, light-irised individuals may have more visible nevi due to contrast against lighter background, and are at higher risk of iris melanoma if transformation occurs
- Fair skin complexion and phototype I–II: Lower melanin photoprotection; associated with higher rates of all melanocytic lesions
- Personal history of dysplastic nevi (atypical mole syndrome): Patients with multiple atypical skin nevi have a higher overall melanocytic risk; iris nevus monitoring is particularly important in this group
- Oculodermal melanocytosis (naevus of Ota): Congenital unilateral periocular skin hyperpigmentation with ipsilateral uveal melanocytosis; significantly increased lifetime risk of uveal melanoma (approximately 1:400 vs 1:13,000 in the general population); all iris lesions in Ota patients require close lifelong surveillance
- UV radiation exposure: Less well established for iris nevi than for posterior uveal melanoma; UV-protective sunglasses with UV-blocking lenses are a sensible precaution
- Family history of uveal melanoma: Rare familial uveal melanoma syndromes (BAP1 tumour predisposition syndrome) increase risk of uveal melanocytic lesions including iris nevi and their transformation
Slit-Lamp Biomicroscopy — Benign Features
- Size: Small — typically <3 mm in basal diameter and <1 mm in height; lesions approaching or exceeding these dimensions require heightened suspicion
- Flat or minimally elevated: Iris surface topography: benign nevi are flat to slightly raised; distinctly elevated lesions (>1 mm) suggest melanoma
- Well-defined, regular borders: Smooth, circumscribed edge without irregular or feathered margin; distinct from the infiltrating, irregular borders of melanoma
- Dark brown to black colour: Homogeneous, uniform brown-black pigmentation; heterogeneous colour, amelanotic areas, or very intense jet-black colouration (suggesting melanocytoma) warrant careful assessment
- Common location — inferior iris: Most frequently found in the inferior temporal or inferior nasal quadrant; any quadrant can be affected; clock-hour position should be documented precisely
- No distortion of adjacent iris architecture: The neighbouring iris crypts and stroma remain undisturbed; pupil shape and size are normal; absence of corectopia or ectropion uveae
- No intrinsic vascularity: No visible feeder vessels on slit-lamp or fluorescein angiography; absence of sentinel vessels (dilated episcleral vessels leading toward the lesion)
- Does not transilluminate: Solid lesion on retroillumination; important for differentiating from iris cysts (which transilluminate brightly)
Warning Signs Suggesting Malignant Transformation (Refer Urgently)
- Documented growth in any dimension >0.5 mm compared to previous photographs
- Development of new intrinsic vascularity (feeder/sentinel vessels)
- Increase in elevation (>1 mm height)
- Irregular or infiltrating borders
- Secondary glaucoma or elevated IOP (from TM seeding)
- Hyphema (bleeding from a lesion)
- Satellite lesions or seeding visible in anterior chamber
- Virtually always asymptomatic: The overwhelming majority of iris nevi cause no visual symptoms whatsoever; the lesion is discovered incidentally during routine slit-lamp examination, glaucoma screening, or dilated fundus examination
- Cosmetic concern: Rarely, a patient may notice a dark spot on their iris (particularly in a light-coloured iris where contrast is high) and present for evaluation of the cosmetic appearance; anxiety about the lesion being malignant is a common presenting concern
- Mild photophobia (exceptional): Very large iris nevi placed centrally that impair iris sphincter function could theoretically cause mild photophobia, but this is extraordinarily rare for a truly benign small nevus
- No pain: A painful iris lesion should not be attributed to a benign nevus — pain suggests secondary glaucoma, inflammation, or another diagnosis
Malignant Transformation to Iris Melanoma
The most clinically significant potential complication, though rare (<1% lifetime risk for iris nevi — substantially lower than the ~2% annual transformation risk for posterior uveal nevi). Transformation is signalled by documented growth, development of vascularity, irregular borders, secondary glaucoma, or hyphema. Early detection through serial monitoring and timely referral for biopsy/treatment is the goal of surveillance protocols.
Secondary Glaucoma (Rare)
Very large benign nevi may rarely seed melanocytic cells into the anterior chamber and trabecular meshwork, causing pigmentary-type glaucoma. This is more characteristic of iris melanocytoma (which regularly sheds pigment) and iris melanoma than of typical small benign nevi. Any new-onset glaucoma in a patient with a known iris lesion should trigger evaluation for TM seeding and possible malignant transformation.
Cataract (Very Rare)
An exceptionally large iris nevus situated near the lens equator could theoretically contact the anterior lens capsule and cause a localised, progressive cataract — an extremely rare occurrence with small benign nevi but noted in case reports of large melanocytomas.
Patient Anxiety
Discovery of an iris lesion can cause significant patient anxiety due to fear of cancer. Clear communication about the benign nature of iris nevi, the very low transformation risk, and the purpose and reassuring nature of serial monitoring is an important aspect of clinical management.
- Naevus of Ota (oculodermal melanocytosis): Congenital unilateral periocular skin melanocytosis with ipsilateral uveal, episcleral, and orbital melanocytosis; associated with a significantly elevated lifetime risk of uveal melanoma on the affected side (approximately 1:400 lifetime risk vs 1:13,000 in the general population); iris nevi in the context of naevus of Ota require lifelong surveillance with a lower threshold for referral; scleral involvement appears blue/grey; requires concurrent monitoring for choroidal melanoma
- BAP1 tumour predisposition syndrome: Germline BAP1 mutations predispose to uveal melanoma, mesothelioma, cutaneous melanoma, renal cell carcinoma, and other cancers; iris nevi in BAP1 carriers require heightened monitoring; family history of uveal melanoma warrants genetic counselling referral
- Atypical mole syndrome (dysplastic nevus syndrome): Multiple cutaneous atypical nevi with increased risk of cutaneous melanoma; associated with higher overall melanocytic lesion risk including uveal lesions; systemic dermatological monitoring is important
- Isolated iris nevi (no systemic associations): For the typical patient with a small solitary iris nevus on a normal background iris, no systemic melanoma syndrome is implied; no systemic investigation is required unless there are other clinical features suggesting a melanoma predisposition syndrome
- Slit-lamp biomicroscopy with photographic documentation (mandatory at first visit): High-magnification slit-lamp examination with direct, retroillumination, and specular illumination techniques; document clock-hour position, maximum basal diameter (two dimensions), height estimate, colour, border characteristics, surface texture, vascularity, and relationship to pupillary margin; anterior segment photography at every visit for serial comparison
- Retroillumination: Essential to determine whether a lesion transilluminates (cyst — does transilluminate) or is solid (nevus — does not transilluminate); shine a beam through the pupil from an angle and observe the iris from the front
- Ultrasound biomicroscopy (UBM): 50 MHz UBM differentiates solid lesion (nevus — echogenic solid mass) from cystic lesion (iris cyst — echo-poor/hollow interior); documents lesion height precisely; rules out posterior extension; identifies ciliary body involvement
- Fluorescein iris angiography (FIA): Performed when vascular features are in question; benign nevi show no intrinsic vascularity or leakage on FIA; melanoma shows intrinsic feeder vessels and leakage; not required for clearly benign small stable nevi but invaluable when malignant transformation is suspected
- Serial slit-lamp photography (monitoring protocol): Every 3–6 months for the first year after initial diagnosis; annually thereafter if stable; any documented change triggers urgent ophthalmology referral for further evaluation
- IOP monitoring: At every visit; elevated IOP in the context of an iris lesion may indicate TM seeding from melanocytic cells, raising concern for malignant transformation or melanocytoma
- Fine needle aspiration biopsy (FNAB): Not performed for clearly benign iris nevi; reserved for lesions with equivocal features, suspected melanoma, or prior to radiation treatment; performed by specialist ocular oncologists; provides cytological diagnosis and, increasingly, prognostic molecular analysis (chromosome 3 status)
- Anterior segment OCT: Non-contact imaging of iris lesion topography; documents elevation, internal reflectivity, and border characteristics; useful adjunct to UBM for superficial anterior segment lesions
1. Observation (Standard Management for Benign Iris Nevus)
Serial observation with photographic documentation is the standard of care for all stable benign iris nevi. No pharmacological treatment is required. No surgical treatment is indicated for a stable, benign lesion. The monitoring schedule: anterior segment photography at every examination; first follow-up at 3–6 months after initial documentation; then annually if stable. Document at each visit: clock-hour position, maximum basal diameter (two perpendicular measurements), estimated height, colour, borders, vascularity, and any change from previous photographs.
2. Documentation Protocol (Every Visit)
- Clock-hour position (e.g., 5 o'clock in left eye)
- Maximum basal diameter in two dimensions (e.g., 2.1 × 1.8 mm)
- Height: flat, <1 mm, 1–2 mm, >2 mm
- Colour: light brown, dark brown, black; homogeneous or heterogeneous
- Border: well-defined/regular vs irregular/infiltrating
- Vascularity: absent vs present (feeder vessels/sentinel vessels)
- Pupil: central, undistorted vs corectopia
- IOP both eyes
- Comparison to previous photography: stable vs changed
3. Referral Triggers (Urgent Ophthalmology Referral)
- Documented growth of >0.5 mm in any dimension compared to previous photography
- Development of new intrinsic vascularity (feeder or sentinel vessels)
- Increase in elevation above 1 mm
- Irregular, infiltrating, or feathered borders
- Secondary glaucoma or IOP elevation not otherwise explained
- Hyphema (anterior chamber haemorrhage)
- Any lesion appearing >3 mm at initial presentation (should be referred at first encounter for specialist evaluation)
- Patient with naevus of Ota or BAP1 syndrome (lower threshold for referral)
4. Treatment (Specialist — Iris Melanoma Suspected)
Treatment is reserved for lesions with documented growth or confirmed iris melanoma: surgical iridectomy (sector or complete iridocyclectomy for small-to-medium tumours), plaque brachytherapy (palladium-103 or ruthenium-106 plaque), proton beam radiotherapy, or enucleation for large tumours or failed local treatment. These are specialist oncology decisions not within optometric scope of practice.
Singapore Optometry Scope Note: Optometrists must photograph ALL iris lesions at the first clinical encounter without exception — this is the most critical step in iris nevus management. Document precise measurements (clock-hour position, basal diameter in two dimensions, elevation, colour, borders, vascularity). Establish a monitoring schedule: 3–6 monthly for the first year, then annually if stable. Understand the clinical features that distinguish a benign nevus from potential melanoma (growth, vascularity, elevation, irregular borders). Refer promptly if any of the growth criteria are met. Do not reassure patients that a lesion is "definitely benign" without serial photographic confirmation of stability — the first examination establishes only initial morphology; stability over time is required to confirm benign behaviour. Patients with naevus of Ota require enhanced surveillance for both iris and posterior uveal melanoma for their entire lifetime.
- Excellent for stable nevi: The vast majority of iris nevi remain stable and clinically insignificant for the patient's entire lifetime; they do not cause visual impairment, pain, or systemic disease
- Malignant transformation rate: Estimated lifetime risk of malignant transformation is <1% — substantially lower than posterior uveal nevi (~1:8,000 per year transformation risk) and far lower than choroidal melanoma incidence; iris melanoma itself, when it occurs, has a better prognosis than posterior uveal melanoma due to earlier detection and smaller tumour size at diagnosis
- Iris melanoma prognosis (if transformation occurs): Iris melanoma carries a lower metastatic risk (~3–5% at 10 years) compared to posterior uveal melanoma (~15–25% at 10 years); early treatment (iridectomy for small lesions) is curative in most cases; prognosis worsens with tumour involving the ciliary body
- Naevus of Ota patients: Significantly elevated lifetime risk (~1:400 lifetime); requires lifelong enhanced surveillance; uveal melanoma arising in Ota patients tends to have a similar prognosis to other uveal melanoma when matched for tumour size and location
- Spontaneous regression: Does not occur; nevi either remain stable or (rarely) grow; a lesion that appears to have decreased in size should prompt investigation for amelanotic change rather than true regression
| Condition | Key Differentiator from Iris Nevus |
|---|---|
| Iris melanoma | Documented growth (>0.5 mm); elevated (>1 mm height); irregular borders; intrinsic vascularity (feeder vessels); sentinel episcleral vessels; TM seeding; hyphema; secondary glaucoma; tapioca variant (nodular surface texture) |
| Iris freckle | Flat, superficial, no stromal involvement; multiple lesions common; very common in general population (>50%); no malignant potential; no height on slit-lamp; no UBM solid mass |
| Iris melanocytoma | Intensely jet-black colouration (virtually black — distinguishable from dark brown nevi); often larger; irregular surface; can shed pigment cells causing melanomalytic glaucoma; UBM shows deeply infiltrative solid lesion; morphologically distinctive |
| Iris cyst (epithelial or stromal) | Transilluminates brightly (hollow interior); UBM shows echo-poor cavity; typically smooth, round, translucent surface; lighter colour than nevus; can arise from pupillary margin (primary) or post-traumatic/iatrogenic (secondary) |
| Iris foreign body | History of ocular trauma; metallic lustre or irregular surface; X-ray or CT orbit confirms metal density; UBM shows acoustic shadow; may have localised iris perforation; haemosiderosis if iron-containing |
| Lisch nodules (NF1) | Multiple bilateral dome-shaped tan/brown nodules on iris surface; associated with neurofibromatosis type 1 (café-au-lait spots, axillary freckling, neurofibromas); no malignant potential; hamartomatous glial lesions not melanocytic |
| Tapioca melanoma | Amelanotic or light-coloured, multiple small nodular surface deposits; gelatinous or tapioca-pearl appearance; rare variant of iris melanoma; may be confused with iris cysts or Lisch nodules; FIA shows intrinsic vascularity |
- Shields CL, Shields JA, Materin MA, Gershenbaum E, Singh AD, Smith A. Iris melanoma: risk factors for metastasis in 169 consecutive patients. Ophthalmology. 2001;108(1):172–178.
- Kaliki S, Shields CL, Singh AD, et al. Iris nevus growth into melanoma: clinical predictors in 333 cases. Ophthalmology. 2019;126(8):1156–1166.
- Freidman EC, Shields CL, Shields JA. Imaging of iris lesions with optical coherence tomography. Ophthalmic Surg Lasers Imaging. 2012;43:S5–S10.
- Mashayekhi A, Shields CL, Materin MA, et al. Optical coherence tomography of choroidal nevus in 120 cases: delineation of risk factors for transformation into melanoma. Ophthalmology. 2008;115(9):1580–1586.
- Shields JA, Shields CL. Intraocular Tumors: A Text and Atlas. Philadelphia: WB Saunders; 1992. Chapter on iris tumours.
- Shields CL, Kaliki S, Hutchinson A, et al. Iris nevus growth into melanoma: analysis of 1611 consecutive eyes. Ophthalmology. 2013;120(4):764–772.
- Singh AD, Kalyani P, Topham A. Estimating the risk of malignant transformation of a choroidal nevus. Ophthalmology. 2005;112(10):1784–1789.