PATHOGENESIS

Ocular melanocytosis represents a focal proliferation of subepithelial melanocytes.

CLINICAL PRESENTATION

Patches of episcleral pigmentation appear slate gray through the normal conjunctiva (Fig 12-8) and are immobile and usually unilateral. Affected patients may have a diffuse nevus of the uvea, evident as increased pigmentation of the iris and choroid. In approximately 50% of patients with ocular melanocytosis, there is ipsilateral dermal melanocytosis and a proliferation of dermal melanocytes in the periocular skin of the first and second dermatomes of cranial nerve V. The combined ocular and cutaneous pigmentations are referred to as oculodermal melanocytosis (nevus of Ota). Approximately 5% of cases are bilateral. Table 12-3 compares the various pigmented lesions of the conjunctiva.

Table 12-2 Tumors and Related Conditions of Neuroectodermal Cells of the Ocular Surface

Figure 12-8 Episcleral pigmentation in a patient with congenital ocular melanocytosis.

(Courtesy of Kathryn Colby, MD, PhD.)

In 10% of patients with ocular melanocytosis, secondary glaucoma occurs in the affected eye. Malignant transformation is possible but rare and seems to occur only in patients with fair complexions. Malignant melanoma can develop in the skin, conjunctiva, uvea, or orbit. The lifetime risk of uveal melanoma in a patient with ocular melanocytosis is about 1 in 400—significantly greater than the approximate 6-per-million risk of the general population.

Table 12-3 Clinical Comparison of Conjunctival Pigmented Lesions

CLINICAL PRESENTATION

A nevus near the limbus is usually almost flat. Nevi appearing elsewhere on the bulbar conjunctiva, plica semilunaris, caruncle, or eyelid margin tend to be elevated. Pigmentation of conjunctival nevi is variable: they may be light tan to brown or amelanotic (15% of cases; Fig 12-9). A subepithelial nevus often has a cobblestone appearance.

Small epithelial inclusion cysts occur within approximately half of all conjunctival nevi, particularly the compound or subepithelial varieties. Secretion of mucin by goblet cells in the inclusion cysts can cause a nevus to enlarge, giving a false impression of malignant change. Cellular proliferation may induce secondary lymphocytic inflammation. Rapid enlargement can occur at puberty, giving rise to a clinical impression of conjunctival melanoma. An amelanotic, vascularized nevus, when inflamed, may resemble an angioma, or it may be misdiagnosed as chronic conjunctivitis. See Table 12-3 for a clinical comparison of the various pigmented lesions of the conjunctiva.

Figure 12-9 Amelanotic conjunctival nevus.

(Courtesy of Kathryn Colby, MD, PhD.)

Jakobiec FA, Sandhu H, Bhat P, Colby K. Bilateral conjunctival melanocytic nevi of simultaneous onset simulating conjunctivitis in a child. Cornea. 2010;29(8):937–940.

Shields CL, Fasiuddin AF, Mashayekhi A, Shields JA. Conjunctival nevi: clinical features and natural course in 410 consecutive patients. Arch Ophthalmol. 2004;122(2):167–175.

MANAGEMENT

Conjunctival nevi rarely become malignant and can be followed with an examination every 6–12 months that includes serial photography or detailed slit-lamp drawings incorporating dimensional measurements. Excisional biopsy should be performed on lesions that show suspicious change or growth. A biopsy should also be performed for pigmented lesions on the palpebral conjunctiva or cornea or in the fornix, as nevi are rare in these locations.