Dr. Tofflemire,

Thank you in advance for answering my question. My cat, Gladys, has a brown spot in her eye. I noticed it in 2019 and its been getting bigger ever since. She doesn’t seem bothered by it, but is this normal?


Hi Jen,

I would clinically describe the changes to Gladys’ eye as iris hyperpigmentation. In cats, the most common causes are iris melanosis and feline diffuse iris melanoma.   

Iris melanosis is a benign, non-cancerous process without apparent effect on comfort, vision, or health of other ocular structures.  However, progression of the hyperpigmentation, both in surface area and color, is common. Because the condition has the potential for transformation into feline diffuse iris melanoma, it should be considered pre-cancerous.   

Feline diffuse iris melanoma is the most common intraocular tumor in cats, but distinguishing between melanosis and melanoma can be difficult, often relying on subtle changes like:

– Impaired iris function (ie. misshapen or asymmetrical pupil)

– Pigmented cellular debris floating within the aqueous humor

– Alteration of the iris texture.   

Early recognition of these changes requires slit-lamp biomicroscopy by a veterinary ophthalmologist. In some cases, a biopsy of the affected tissue may be informative. Unlike iris melanosis, late stages of feline diffuse iris melanoma tend to cause secondary issues like uveitis, cataracts, and glaucoma.

Unfortunately, due to the potential for metastasis, enucleation (surgical eye removal) is often the most appropriate treatment once a feline diffuse iris melanoma has developed. If your cat (or dog) has progressive pigmentation to his or her eye, I encourage you to pursue an evaluation with a veterinary ophthalmologist.   

-Dr. Tofflemire