Medically known as iris freckles, iris freckles, iris hyperpigmentation, melanoma and iris melanosis, as the name would suggest, brown spots occur in the iris (the coloured part of the eye) and are reasonably common. They are similar to moles or pigment spots and are seen most often in cats who are middle-aged to senior.
The condition is caused by the proliferation of melanocytes, which are cells responsible for the production of pigmentation. For the sake of simplicity, we will refer to the benign form as iris melanosis and the cancerous form as malignant melanomas.
Dark spots can develop in cats of any eye colour and may be cancerous (malignant) or benign. It is also possible for benign iris melanosis to slowly progress into malignant melanoma, although this is quite rare. More often than the above, iris melanomas lead to glaucoma, a condition caused by increased pressure within the eyeball. Glaucoma causes distorted vision and can be extremely painful. Malignant melanomas have the potential to metastasise (spread) to other parts of the body, especially the lungs and the liver.
Areas of dark brown pigmentation within the iris. There may be one or multiple areas of pigmentation. Spots usually only occur in one eye, but in some cases, both eyes can be affected. Spots may start small and gradually increase in size and become darker. Where multiple spots are present, as they grow in size, they may merge.
Iris melanosis is flat and should not protrude above the surface of the iris. Malignant melanomas are lumpy, raised and can cause distortion to the surface of the eye.
While iris melanosis is painless, if infiltration of the neighbouring drainage angle occurs, glaucoma, an extremely painful increase in intraocular pressure can develop.
A veterinarian should evaluate pigmented spots in your cat’s eye to determine if they are benign iris melanosis or malignant melanoma.
Tests he will perform may include:
- A slip lamp examination to check the eye under magnification.
- Fine needle biopsy to determine if the lesion is benign or cancerous.
Your veterinarian may refer your cat to a specialist eye veterinarian, (known as an ophthalmologist) for diagnosis and treatment.
- A wait and see approach recommended for cats with iris melanosis. You will need to regularly check your cat’s eye(s) to make sure the spots aren’t growing in size.
- Re-assessment by a veterinarian every six months, with comparison photos taken.
- Destruction of the cells with a laser or removal of the entire eye are the treatment of choice for malignant melanomas.
- Removal of the eye may be necessary if glaucoma has developed.