An iris nevus is a variably pigmented lesion of the iris stroma that causes minimal distortion of the iris architecture. It is a benign tumor, likely congenital in origin, that contains increased numbers of specialized melanocytes (nevus cells). Many of these lesions are small, produce no symptoms, and are recognized incidentally during routine ophthalmic examination. Their prevalence is uncertain, although iris nevi are thought to occur more frequently in patients with neurofibromatosis type I.
Iris nevi should be distinguished from iris freckles, which are flat lesions associated with an increased amount of melanin within cells and are not tumors (Fig 17-1A). Iris freckles may be associated with ultraviolet (UV) light exposure and are more prevalent in el derly individuals. Although iris freckles have no malignant potential, numerous iris freckles may be associated with increased risk for cutaneous melanoma, which is similarly associated with an elevated lifetime exposure to UV light. Individuals with more than 3 iris freckles may benefit from routine skin evaluation by a dermatologist.
Ophthalmoscopically, iris nevi present in 2 forms: (1) circumscribed iris nevi, which are flat to nodular, solitary or multiple, involving a discrete portion of the iris; and (2) diffuse iris nevi, which may involve an entire sector or, in rare instances, the entire iris. Iris nevi may cause ectropion uveae (Fig 17-1B) and, occasionally, a sectoral cataract.
Iris nevi are best evaluated by slit-lamp biomicroscopy coupled with gonioscopy. The clinician should pay specific attention to lesions involving the angle in order to rule out a ciliary body tumor, as the most important differential diagnosis is iris or ciliary body melanoma. High-frequency ultrasound biomicroscopy (UBM) is helpful in the evaluation of lesions that involve the angle as it can depict a ciliary body component. Examples of the clinical appearance of iris freckles and nevi are shown on page 306 in Figure 17-1.
Iris nevi do not usually require treatment beyond observation, including photographic documentation.
Excerpted from BCSC 2020-2021 series: Section 4 - Ophthalmic Pathology and Intraocular Tumors. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.