Choroidal Naevus vs Melanoma: TFSOM-DIM Risk Factors, Imaging and When to Refer
Last updated: November 2026
A flat, grey-brown spot under the retina is one of the commonest incidental findings in a dilated fundus examination. Almost all are benign naevi. The skill is to recognise the few that are small melanomas, or naevi likely to become one, and refer them early, because survival in uveal melanoma depends on tumour size at treatment. A short mnemonic and four simple scans do most of the work.
The typical choroidal naevus
- Flat or minimally elevated (under 2 mm thick), slate-grey to brown, with feathery or well-defined margins, usually under 5 mm across.
- Found in about 5–8% of white adults and less often in people of Asian and African descent.
- Signs of chronicity are reassuring: overlying drusen and RPE atrophy or hyperplasia, and a surrounding depigmented halo.
- The estimated rate of transformation of a naevus into melanoma is low, about 1 in 8,800 per year in white populations, but because naevi are common, every clinician sees the occasional one that grows.
TFSOM-DIM: the risk factors for growth
Shields and colleagues (2019) updated the older "TFSOM-UHHD" mnemonic using multimodal imaging in over 2,000 naevi. Each factor is linked to the scan that shows it best.
| Letter | Risk factor | Best shown by |
|---|---|---|
| T | Thickness over 2 mm | Ultrasound (B-scan) |
| F | Fluid: subretinal fluid | OCT |
| S | Symptoms: vision loss (to about 6/15 or worse) or photopsia | Visual acuity, history |
| O | Orange pigment (lipofuscin) | Fundus autofluorescence: bright hyperautofluorescent spots |
| M | Melanoma hollow: low internal reflectivity | Ultrasound (A- or B-scan) |
| DIM | DIaMeter over 5 mm | Fundus photography |
Five-year risk of growth into melanoma by the number of factors: none, about 1%; one, about 11%; two, about 22%; three or more, about 34% (three) rising to about 50% (four or five).
The older mnemonic, still in many textbooks, is TFSOM-UHHD: To Find Small Ocular Melanoma Using Helpful Hints Daily, which adds Margin within 3 mm of the disc, Ultrasound hollowness, Halo absent and Drusen absent. Reassuring signs are the opposite: drusen, a halo, and a flat, thin lesion with no fluid.
What each scan shows
| Test | Naevus | Suspicious for melanoma |
|---|---|---|
| Wide-field colour photograph | Baseline for comparison: the single most useful test | Documented growth on serial photos |
| Fundus autofluorescence | Mostly iso- or hypoautofluorescent; drusen may be bright | Bright clumps (orange pigment); overlying fluid tracks show bright gravitational patterns |
| OCT (enhanced depth imaging) | Thin, smooth dome; overlying drusen; RPE changes | Subretinal fluid, "shaggy" photoreceptors, thickness increasing over time |
| B-scan and A-scan ultrasound | Flat or thin, high internal reflectivity | Thickness over 2 mm, low to medium internal reflectivity (acoustic hollowness), choroidal excavation; a collar-stud (mushroom) shape means the tumour has broken through Bruch membrane and is diagnostic of melanoma |
| FFA and ICGA | Usually not needed | Intrinsic tumour circulation ("double circulation") on FFA in larger tumours; helps rule out haemangioma |
Look-alikes (the differential diagnosis)
| Lesion | Clues |
|---|---|
| Congenital hypertrophy of the RPE (CHRPE) | Flat, jet-black, sharply defined, often with depigmented lacunae and a pale halo; does not thicken. Multiple bilateral "bear-track" or pisciform lesions: think familial adenomatous polyposis (Gardner syndrome) |
| Melanocytoma of the optic disc | Very dark black lesion on or next to the disc, with feathery edges into the nerve fibre layer; usually stable |
| Circumscribed choroidal haemangioma | Orange-red dome near the disc or macula; high internal reflectivity on ultrasound; early bright filling and late "wash-out" on ICGA |
| Choroidal metastasis | Creamy-yellow, often multiple or bilateral, with a lot of subretinal fluid; ask about breast and lung cancer |
| Peripheral exudative haemorrhagic chorioretinopathy | Elderly patient, peripheral dark haemorrhagic mass, often bilateral; resolves over months |
| Eccentric disciform scar or haemorrhage (CNV or PCV) | Dark subretinal or sub-RPE blood with drusen or other AMD signs; changes over weeks |
| Choroidal osteoma | Orange-yellow plaque in a young woman; very bright on ultrasound with shadowing (calcium) |
| Posterior scleritis (nodular) | Pain, T-sign on B-scan |
Size groups (COMS)
| Group | Thickness (apex height) | Largest basal diameter |
|---|---|---|
| Small | 1.0–2.5 mm | 5–16 mm |
| Medium | 2.5–10 mm | 16 mm or less |
| Large | Over 10 mm | Or over 16 mm (or over 8 mm thick near the disc) |
Staging today uses the AJCC/TNM system (T1–T4 by thickness and diameter, plus ciliary body involvement and extraocular extension). See our COMS findings page.
Follow-up and referral: a practical plan
| Situation | Plan |
|---|---|
| Flat typical naevus, no risk factors, drusen present | Baseline photograph (and ideally OCT); review at 6 months, then yearly |
| One or two risk factors | Photograph, OCT, autofluorescence and ultrasound; review every 3–4 months at first |
| Three or more risk factors, or documented growth | Refer to an ocular oncologist: this is likely a small melanoma |
| Collar-stud shape, thickness over 3 mm, or extrascleral spread | Urgent ocular oncology referral |
Always record the size in disc diameters or millimetres, the distance to the disc and fovea, and take photographs with the same camera each time; growth is the single strongest sign. Tell the patient why they are being followed so they keep the appointments.
If it is melanoma
- Treatment depends on size and location: plaque brachytherapy (iodine-125 or ruthenium-106) for most small and medium tumours, proton beam therapy, and enucleation for large tumours or blind painful eyes. Transpupillary thermotherapy alone is no longer favoured because of recurrences.
- Prognosis is guided by tumour size, ciliary body involvement, and cytogenetics or gene expression profiling (monosomy 3, BAP1 loss, and class 2 gene expression profile carry a high risk of metastasis).
- Metastasis goes mainly to the liver, so patients have regular liver imaging. Tebentafusp was approved in 2022 for HLA-A*02:01-positive metastatic uveal melanoma.
- For COMS trial results on brachytherapy versus enucleation, see COMS findings.
Where residents slip
- Calling any elevated pigmented lesion "naevus" without ultrasound.
- Ignoring orange pigment: on autofluorescence it is bright and a strong risk factor.
- Forgetting to photograph at baseline: growth cannot be judged from memory.
- Mistaking a flat, jet-black CHRPE for melanoma, or a melanoma for a CHRPE.
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Related: Ocular Tumours: Eyelid, Conjunctiva, Uvea and Orbit, COMS Trial Findings for Choroidal Melanoma, B-scan Ultrasound Patterns: RD, PVD, Choroidal Detachment and Masses, FFA and ICG Angiography Patterns: Quick Reference Card, OCT Macula Reference Card: Normal Thickness, DME and Hole Staging.
Key sources
- Shields CL, Dalvin LA, Ancona-Lezama D, et al. Choroidal nevus imaging features in 3,806 cases and risk factors for transformation into melanoma in 2,355 cases (TFSOM-DIM). Retina. 2019;39:1840-1851
- Singh AD, Kalyani P, Topham A. Estimating the risk of malignant transformation of a choroidal nevus. Ophthalmology. 2005;112:1784-1789
- Collaborative Ocular Melanoma Study Group. COMS Report No. 18. Arch Ophthalmol. 2001;119:969-982
- Nathan P, et al. Overall survival benefit with tebentafusp in metastatic uveal melanoma. N Engl J Med. 2021;385:1196-1206
- Review of Optometry: Mnemonic helps catch small choroidal melanoma early (summary of the TFSOM-DIM risk figures)
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