Answer 3 | Ophthalmic Pathology

Comment: Diffuse iris melanoma in cats can appear deceptively benign histologically. In early cases, rows of fairly well differentiated melanocytes along the anterior face of the iris may be the only histologic feature. The foci tend to enlarge, invade the iridial stroma and shed neoplastic cells into the anterior chamber. Invasion of the iridociliary junction by such exfoliated cells result in glaucoma. Contrary to some reports, there can be invasion of limbal blood vessels and early tumor metastasis.
Selected Reference: Acland GM, IW McLean, GD Aguirre, R Truksa. Diffuse melanoma in cats. J Am Vet Med Assoc, 176; 52-56: 1980
	Fig 2. This section of iris has clustered accumulations of melanin-containing cells with dark basophilic nuclei on the anterior face of the iris. Cells are present in the underlying stroma. Mitoses are rare. Melanin containing macrophages are also present in the iridial stroma.

	Fig 3. Dense accumulations of melanin containing cells with larger, more vesicular nuclei infiltrate the entire iridial stroma. Mitoses are also rare.

Diagnosis: Diffuse iris melanoma

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