The most common primary anterior uveal tumors include melanoma of the iris and ciliary body, and adenomas or adenocarcinomas of the ciliary body. Severe uveitis
Melanomas are the most common primary uveal tumor. Cats most commonly develop a diffuse, flat melanoma of the iris that begins as progressive pigmentation (darkening) of the surface of the iris. This color change is often a slow process and may develop over several months to years. Several golden-brown pigmented spots or "freckles" may develop simultaneously on the iris that progressively enlarge, grow together and become irregular along their surfaces. The migration of cancerous pigmented cells (melanocytes) into the iris eventually causes the iris to thicken and the shape of the pupil may become distorted. The pupil often remains larger than the opposite normal pupil. Glaucoma may also develop.
Some melanomas lack the typical brown/black pigmentation and are pink/white in color. These are called amelanotic melanomas. All amelanotic melanomas are considered malignant.
All anterior uveal melanomas have malignant potential. Metastatic disease related to uveal melanoma is more commonly observed in the cat than in the dog. Metastasis may occur as late as one to three years after eye removal and usually involves the lymph nodes, lungs and liver.
Primary sarcomas of the eye may develop in cats months to years after an event of ocular trauma or injury. These tumors are highly malignant and necessitate immediate removal of the eye.
The most common secondary anterior uveal tumor is lymphosarcoma. Usually the lymphosarcoma in the eye is one component of widespread cancer throughout the body. It is rare for lymphosarcoma to appear in the eye alone. Other uveal tumors represent the spread of malignant tumors from some other location in the body, such as breast cancer, cancer of the kidney or cancer of the thyroid. Metastasis to the anterior uvea from any kind of malignant tumor is possible, although most metastatic tumors appear in the choroid rather than in the anterior uvea.
A few other ophthalmic diseases or conditions can mimic the symptoms similar to those observed with anterior uveal tumors. It is important to exclude these conditions before establishing a conclusive diagnosis.
Traumatic injuries to the eye
Chronic anterior uveitis with hyperpigmentation of the iris
Conjunctival and scleral tumors
Conjunctival and scleral inflammatory masses that look like tumors
Old bleeding into the anterior chamber of the eye