The common iris nevus is covered well in the literature (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29). In contrast to iris freckle, a nevus effaces the architecture of the iris stroma. Iris freckle occurs in about 60% of the population and probably has no malignant potential, whereas an iris nevus occurs in 5% of the population and may rarely give rise to malignant melanoma. There are conflicting reports regarding a relationship between iris nevus and choroidal melanoma (7,12,25). Iris nevus, like other melanocytic uveal tumors, shows a predilection for whites and becomes clinically apparent during puberty or young adulthood.

The size, shape, and pigmentation of iris nevus can vary from case to case (6). It can be small and circumscribed, large and diffuse, or flat to dome shaped, and can sometimes show satellite seeding into the adjacent iris. It can be entirely amelanotic and transparent, or it can be deeply pigmented. Greater than 80% are located in the inferior half of the iris (15). It was once believed that an irregular pupil, angle involvement, secondary cataract, secondary cyst, tapioca configuration, and adjacent transcleral extension were signs of malignant transformation. However, we now know that many iris nevi can produce such secondary changes (1). Overall, about 5% of borderline suspicious iris nevi show growth within 5 years after diagnosis and evolve into low-grade melanoma (5). Secondary glaucoma associated with iris nevus is extremely rare, and significant elevated intraocular pressure should raise suspicion of iris melanoma. Iris nevus can frequently be associated with a pigment epithelial cyst immediately posterior to the lesion (1,17).

A variation of iris nevus is melanocytoma, a lesion that may simulate melanoma and is best known to occur on the optic disc. In contrast to ordinary nevus and melanoma, it is more deeply pigmented and can readily undergo necrosis and pigment dispersion and can induce secondary glaucoma (2,3,9,11,29). The glaucoma seen with melanocytoma is due to obstruction of trabecular meshwork by melanophages that contain pigment liberated by necrotic melanocytoma cells. Hence, this condition has been termed melanocytomalytic glaucoma (3). Histopathologically confirmed iris melanocytoma has been documented to show clinical enlargement in young children (8). In some instances, iris melanocytoma can represent anterior extension of a larger melanocytoma in the ciliary body (19,20). Like other iris nevi, iris melanocytoma can undergo malignant transformation (1,21,22,29). In such cases, the melanoma component may be only a small focus within the benign lesion.

An unusual variation of iris nevus observed by the authors is an amelanotic lesion that can show growth, suggesting malignancy. When such tumors have come to histopathologic evaluation, it may be difficult for pathologists to determine whether the lesion is benign or malignant microscopically. This condition has been observed to have a familial tendency (16). An iris nevus that has received little mention in the literature is the sector iris nevus. This lesion appears as a well-defined sector of increased pigmented that extends from the pupil to the angle. It can range in size from 1 to >6 clock hours. This lesion is probably congenital, and we consider it to be a localized form of ocular melanocytosis. In some instances, an iris nevus can have a multinodular surface that resembles tapioca. A tapioca nevus can be remarkably similar to tapioca melanoma. Although we are not aware of publications on tapioca nevi, we have diagnosed it on many occasions. Another variation is the diffuse iris nevus (Cogan-Reese syndrome) (10), a condition that may fall in the spectrum of the iridocorneal endothelial syndrome, discussed in Chapter 3.

Histopathologically, iris nevus cells can range from slender spindle cells to rounded cells similar to those seen in melanocytoma of the optic nerve. Rarely, benign epithelioid cells may predominate, suggesting a diagnosis of melanoma (27). In borderline cases, iris nevus may be difficult to differentiate microscopically from a low-grade melanoma (3). Not surprisingly, it has been shown that nucleolar size is statistically smaller in iris nevus than in iris melanoma (13).

Concerning management, the patient should be informed that the chances of malignant transformation are relatively low (1, 2, 3, 4, 5). Baseline photographs and examination every 6 to 12 months is recommended to detect evidence of growth. Fluorescein angiography has little value in diagnosis. Ultrasound biomicroscopy (UBM) can help to detect adjacent ciliary body involvement and to follow the lesion for growth. It can help to differentiate nevus in the angle from cyst. If photographic evidence of growth is documented, then active treatment should be considered. This is covered in the next section on iris melanoma.

The nonpigmented or minimally pigmented iris nevus can resemble a leiomyoma, metastatic carcinoma, lymphoma, and other nonpigmented iris lesions. The term nonpigmented is used here for simplicity, even though some may contain slight pigmentation. Selected examples are illustrated.

Iris nevi can distort the adjacent pupil, involve the anterior chamber angle, produce a secondary cataract or a secondary cyst, and even demonstrate transcleral involvement. Such findings can occur with a nevus and do not necessarily indicate that the lesion is malignant.

Melanocytoma is a deeply pigmented variant of melanocytic nevus. Although most are stable, some can show very slow growth and tumor seeding, similar to melanoma.