--- title: "Choroidal Naevus vs Choroidal Melanoma: Understanding TFSOM-DIM Risk Factors" description: "Most choroidal naevi are harmless, but clinicians become more concerned when a lesion shows validated features linked to growth into melanoma. A practical evidence-based checklist used in ocular oncology is TFSOM-DIM, which captures key \"activity\" signs: ¹ - Thickness >…" url: "https://bluefinvision.com/knowledge-base/topics/conditions-diseases/choroidal-naevus-vs-choroidal-melanoma-understanding-tfsom-dim-risk-factors/" updated: "2026-02-16" category: "Conditions & Diseases" --- # Choroidal Naevus vs Choroidal Melanoma: Understanding TFSOM-DIM Risk Factors Most choroidal naevi are harmless, but clinicians become more concerned when a lesion shows validated features linked to growth into melanoma. A practical evidence-based checklist used in ocular oncology is TFSOM-DIM, which captures key "activity" signs: ¹ - Thickness > 2 mm - Fluid (subretinal fluid on optical coherence tomography) - Symptoms (new blur/distortion/scotoma) - Orange pigment (lipofuscin on autofluorescence) - Margin near the optic disc - Diagnosed hollowness (low internal reflectivity on ultrasound) - I/M: Imaging evidence of suspicious change, and absence of protective chronicity signs such as drusen/halo (depending on the model used) The clinical point is not "a naevus is dangerous because it exists", but: risk rises as objective factors accumulate. Large series show that documented growth is uncommon overall, but the probability increases sharply with multiple risk factors. ¹ ³ Good practice is to measure, not "reassure": baseline photos, OCT and (when needed) ultrasound, then follow-up based on the lesion's risk profile. ² **References** 1. Shields CL, Furuta M, Berman EL, Zahler JD, Hoberman DM, Dinh DH, et al. Choroidal nevus transformation into melanoma: analysis of 2514 consecutive cases. Archives of Ophthalmology. 2009;127(8):981-987. doi:10.1001/archophthalmol.2009.151. PMID: 19667334. 2. Dalvin LA, Shields CL, Ancona-Lezama DA, Yu MD, Di Nicola M, Williams BK Jr, et al. Combination of multimodal imaging features predictive of choroidal nevus transformation into melanoma. British Journal of Ophthalmology. 2019;103(10):1441-1447. doi:10.1136/bjophthalmol-2018-312967. PMID: 30523045. 3. Singh AD, Kalyani P, Topham A. Estimating the risk of malignant transformation of a choroidal nevus. Ophthalmology. 2005;112(10):1784-1789. doi:10.1016/j.ophtha.2005.06.011. PMID: 16154197. **Related Topics** - [When Does a "Freckle" in the Eye Become Concerning?](https://bluefinvision.com/blog/when-does-a-freckle-in-the-eye-become-concerning/) - [What Does a "Freckle in the Eye" Actually Mean? 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