Iris Melanosis and Iris Melanoma in Cats
Feline iris melanosis consists of one or more darkly pigmented areas, nevi, on the anterior iris surface caused by proliferation and accumulation of melanocytes. These areas are small, focal, smooth, brown, and round or irregular. The source describes melanosis as a benign condition that may remain unchanged for years but may sometimes acquire malignant behavior and develop into iris melanoma; therefore regular monitoring is recommended.
If melanosis begins to spread and involves the iris sphincter, pupil shape and size may change and secondary glaucoma may develop, indicating progression. Iris melanosis is not associated in the source with a particular age or iris color. Cats frequently develop a diffuse form of iris melanoma. The neoplasm can spread rapidly and alter pupil shape and mobility and cause secondary glaucoma. It may occasionally be amelanotic, making diagnosis more difficult. Its metastatic potential is described as substantially greater than in dogs, and metastases may be detected years after enucleation.
Treatment
Ophthalmic examination is used for diagnosis, but differentiating benign melanosis from malignant iris melanoma and predicting when melanosis may become malignant can be difficult. A stable or very slowly progressive lesion should be monitored closely. If a lesion spreads rapidly, increases in thickness, or extends to the iris margin, malignant melanoma is suspected; preliminary diagnostic evaluation is followed, after confirmation of suspicion, by laser treatment intended to destroy pigmented lesions according to the source. Secondary glaucoma is an indication for enucleation. If enucleation is performed, the globe should be submitted for histopathology to establish a definitive diagnosis and guide further management.
Iris melanosis in a cat. Small areas of iris hyperpigmentation are visible.
Iris melanosis in a cat.
Iris melanosis in a cat.
Iris melanoma in a cat. A tumor mass is visible on the iris, red arrow, together with pigment accumulation on the anterior lens surface visible through the pupil.
Adapted from the Atlas of Ocular Diseases in Dogs and Cats by Dr. Siniša D. Grozdanić and colleagues. © Animal Eye Consultants of Iowa. The text and clinical images on this page are original content from the authors' own clinical practice and research, and may not be reproduced, distributed, or repurposed without permission.
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