Saad Bidiwala
Introduction
Uveal melanoma arises from melanocytes within the uveal tract, which comprises the iris, ciliary body, and choroid. Although it accounts for only about 5% of all melanoma cases, it remains the most common primary intraocular malignancy in adults. The potential for metastasis, especially to the liver, makes early detection critical. The condition’s exact cause isn’t fully understood, but genetic mutations (e.g., BAP1, GNAQ, GNA11) and certain environmental factors, including ultraviolet light exposure, are implicated. This article breaks down the key clinical features, diagnostic strategies, and treatment options specific to each part of the uveal tract while highlighting how to distinguish benign naevi from malignant melanomas.
Clinical Features
Iris Melanoma
- Appearance: Raised, pigmented, or non-pigmented mass; may distort pupil shape or cause heterochromia.
- Symptoms: Blurred vision, changes in iris color, or secondary glaucoma due to tumor invasion.
- Prognosis: Generally favorable due to earlier detection.
Ciliary Body Melanoma
- Symptoms: Blurred vision, irregular astigmatism, or lens subluxation due to tumor pressure.
- Signs: Gonioscopy may reveal a mass; slit-lamp exam can show anterior lens displacement.
- Challenges: Often detected late due to its hidden location.
Choroidal Melanoma
- Symptoms: Floaters, blurred vision, or visual field shadows; retinal detachment in larger tumors.
- Appearance: Dome-shaped or mushroom-shaped pigmented mass on fundoscopic examination.
Distinguishing Naevus from Melanoma
| Characteristic | Naevus | Melanoma |
| Growth | Stable over time | Gradual enlargement |
| Size | Small, usually <5mm | Larger, typically >5mm |
| Thickness | Thin, <2mm | Thicker, >2mm |
| Subretinal fluid | Absent | Present, suggests activity |
| Orange pigment | Rare | Common, indicates malignancy |
| Borders | Well-defined | Irregular |
| Symptoms | None | Blurred vision, floaters, shadows |
A useful mnemonic for identifying melanomas is “To Find Small Ocular Melanoma”:
- T: Thickness >2mm
- F: Fluid (subretinal)
- S: Symptoms (blurred vision, floaters)
- O: Orange pigment
- M: Margin irregularity
Diagnostic Approach
Clinical Examination
- Slit-lamp Biomicroscopy: Best for detecting iris melanomas.
- Indirect Ophthalmoscopy: Ideal for choroidal or ciliary body tumors.
Imaging
- Ultrasonography (B-scan): Measures tumor thickness and internal reflectivity.
- Optical Coherence Tomography (OCT): Provides high-resolution imaging of retinal detachment.
- Fluorescein Angiography: Assesses lesion vascularity.
Staging and Metastasis
- MRI/CT Scans: Detect liver metastases, common in advanced cases.
- Genetic Testing: Identifies high-risk mutations (e.g., BAP1) for prognosis.
Treatment Strategies
Iris Melanoma
- Small Lesions: Managed conservatively with regular monitoring.
- Larger Lesions: May require iridectomy or radiotherapy.
Ciliary Body and Choroidal Melanoma
The COMS trial helped to guide treatment choice in choroidal melanoma by demonstrating there was no significant difference in mortality between enucleation and brachytherapy (Iodine-125 isotope was used) (1).
- Radiotherapy:
- Brachytherapy: Uses a radioactive plaque for localized treatment.
- Proton Beam Therapy: Provides precision for larger tumors.
- Surgical Intervention:
- Enucleation: For large, non-resectable tumors or severe complications.
Systemic Therapy
- Targeted therapies or immunotherapies in metastatic cases, though outcomes remain poor.
Prognosis
- High risk of metastasis, particularly to the liver (50% of patients within 10 years).
- Early detection significantly improves outcomes for small, localized tumors.
Conclusion
Uveal melanoma is a rare but aggressive malignancy, with clinical features varying depending on its location within the uveal tract. Early diagnosis and intervention are important for improving survival and preserving vision. By understanding the distinctions between benign naevi and melanoma and utilizing advanced imaging and genetic testing, clinicians can better manage this challenging condition.
References
- Margo CE. The Collaborative Ocular Melanoma Study: an overview. Cancer Control. 2004 Sep-Oct;11(5):304-9. doi: 10.1177/107327480401100504. PMID: 15377989.