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. They can occur in cats of any eye colour and may be cancerous (malignant) or benign. 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.
It may be possible for an iris melanosis to slowly progress into a malignant melanoma, although this is quite rare. More often than the above, iris melanomas lead to glaucoma, a condition caused by an 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.
What do these brown spots look like?
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 out small and gradually increase in size and become darker. Where multiple spots are present, as they increase in size, they may merge together.
Iris melanosis are flat and should not protrude above the surface of the iris. By contrast, malignant melanomas are lumpy, raised and may cause distortion to the surface of the eye.
(click to see larger image)
Iris melanosis don't cause pain, however if infiltration of the neighbouring drainage angle, glaucoma can occur.
When to see a veterinarian:
If you notice pigmented spots in your cat's eye he should be evaluated by a veterinarian. Your vet will need to determine if this is a benign iris melanosis or a malignant melanoma. Tests he will perform may include:
- A slip lamp will be used to carefully check the eye. This is a special lamp which helps your veterinarian to see the eye under magnification.
- A fine needle biopsy may be taken for evaluation of the cells to determine if the lesion is benign or cancerous.
Your veterinarian may recommend your cat be seen by a specialist eye vet, known as a ophthalmologist for diagnosis and treatment.
How is it treated?
A wait and see approach is usually recommended for iris melanosis. You will need to regularly check your cat's eye(s) to make sure the spots aren't growing in size. It is usually recommended he be re-assessed by a veterinarian every 6 months, with photos taken for comparison.
Small malignant melanomas may be treated either by destruction of the cells with a laser, or removal of the entire eye (known as enucleation).
If glaucoma has occurred and the eye is painful, it may need to be removed.