SUMMARY: Are you monitoring someone who has a suspicious iris nevus? Do you know someone who has an ‘iris freckle’? Here are two key clinical exam tips that could help you diagnosis
iris melanoma.
Iris melanoma is the least common form of uveal melanoma. Fortunately, the development of metastasis from an iris melanoma is low. However, it is not zero; in fact, diffuse iris melanomas have a high risk of metastatic spread.
Why is making the diagnosis of iris melanoma so challenging? The appearance of iris melanoma is highly variable – pigmented, partly pigmented, vascular, smooth, irregular, etc. There is no ‘classical clinical appearance’ to an iris melanoma like in many cases of posterior choroidal melanoma. Strange-looking iris nevi make all of us nervous. We do not want to miss diagnosing cancer.
Iris melanomas may fool us by the way they look. Let’s think about the biology of a malignant tumor. Malignancies are invasive - actively proliferating cells will eventually manifest as documentable growth. Secondary glaucoma occurs 7.5x more frequently in iris melanomas than posterior choroidal melanoma (UCLA data). But before they show us that they are growing, melanoma cells may invade and obstruct the angle of the anterior chamber where aqueous humor drains. And because tumor cells are microscopic, it might not look like there is angle involvement even on gonioscopy.
Here are the TWO clues:
1. Asymmetric intraocular pressure (IOP): If the IOPs are not the same, which eye is higher? Is it the one with the suspicious iris nevus?
2. Asymmetric cup to disk ratios: The IOPs may not be significantly different, but microscopic angle invasion may be causing nerve fiber layer alterations that reveal themselves as optic nerve cupping.
If you are monitoring a patient with an iris nevus, particularly one that is pigmented, the development of IOP and cup to disk ratio asymmetry between the eyes even without evidence of growth must alert you to the possibility of the lesion being an iris melanoma.
Caveats: not all iris melanomas alter intraocular pressure. A patient could have glaucoma and the iris nevus could be a red herring. Likewise, a person may have asymmetric cup to disk ratios that are physiologic. If you are concerned, refer your patient for a glaucoma evaluation or tumor evaluation. Or if you would like to share your photos with us, send them to tmccannelpatients@jsei.ucla.edu.