Image supplied by Dr Steven Lam, Specsavers Sunbury, VIC
The slit-lamp photograph pictured shows a raised, amelanotic iris melanoma distorting the shape of the pupil and causing out-pouching of the pupillary ruff. This lesion has a distinctive appearance due to the lack of pigment demarcating the lesion and the prominent iris vasculature associated. More typically, iris melanomas present as a light or dark brown pigmented mass causing disruption to the normal iris structure.
There are several risk factors for development of iris melanoma, including:
- Fair skin / light eyes
- Family history of melanoma
- History of atypical moles
Usually, the patient will present asymptomatically, however, iris melanomas may be associated with other sequelae such as sectoral cataract, heterochromia, chronic uveitis, glaucoma (due to infiltration of the anterior chamber angle or pigment dispersion), or spontaneous hyphaema.
Assessment of this type of growth is best performed using anterior slit-lamp examination, IOP measurement, gonioscopy, and OCT anterior segment imaging.
Clinicians should look for the following:
- Growth of an iris nevi or previous documented lesion
- A new iris lesion
- Surface nodularity
- Prominent vasculature
- Irregular surface
- Any of the aforementioned sequelae.
Any suspicious, changing or growing lesion should be referred for ophthalmological assessment and screening for metastasis.
Iris melanomas are a rare form of uveal tract melanoma (UVM).
UVMs account for approximately 5-10% of all melanomas in the body and predominantly involve the ciliary body or choroid, or sometimes both. This makes them the most common primary intraocular malignancy in adults. However, iris melanomas make up only 5% of UVMs.
Progression & Prognosis
Where an iris melanoma is diagnosed, treatment may include brachytherapy (insertion of radioactive implant into the iris), excisional biopsy (fine needle aspiration biopsy or iridectomy) or enucleation. Enucleation is usually only indicated if the iris melanoma is diffuse and involves the angle, ciliary body or other structures of the eye.
Iris melanomas very rarely metastasise as the eye does not have lymphatic vessels. However, if they do, it is via distant metastasis, most commonly to the liver. The rate of metastasis is documented at approximately 3% at 5 years, and 5% at 10 years.