The first sign observed in most cases is a darkening in iris color. The pupil may also change shape, or a raised area on the iris may be seen. As the disease progresses, the tumor can cause glaucoma, resulting in eye redness, squinting, cloudiness of the cornea, vision loss and over time, eye enlargement.
A thorough eye examination, including slit-lamp biomicroscopy, is essential to determine if the pigmented areas are flat or raised, and if there are pigmented cells floating in the anterior chamber. Gonioscopy and ocular ultrasound are performed to determine the extent, depth and size of the tumor. In situations where melanoma is highly suspected, thoracic radiographs, lymph node aspirates and abdominal ultrasound is recommended to assess for potential cancer spread.
For melanosis, serial eye examinations, and initially at frequent intervals, are often recommended. Photographs are taken to document any changes over time.
To differentiate melanosis from melanoma, several parameters are assessed including enlargement and thickening of the pigmented areas, exfoliation of pigmented cells into the anterior chamber, elevations in intraocular pressure, among other features.
For melanosis, other than regular monitoring, no treatment is necessary.
Uveal melanomas in dogs are predominately benign and rarely ever spread to other aspects of the body. However, they slowly grow inside the eye. They eventually cause retinal detachment, cataract formation, and most importantly glaucoma. This form of glaucoma is typically poorly responsive to medical therapy, resulting in significant discomfort and vision loss.
There are several treatment options for uveal melanomas. Treatment recommendations are based upon tumor size and depth, and the species. For small, isolated melanomas, non-invasive laser treatment (ablation) can destroy the tumor. Laser ablation of larger or diffuse iris melanomas often shrinks and slows the growth of the tumors. However, a cure is not often achievable with laser alone. Surgical removal of some tumors is possible and may be combined with cryo (freezing) or laser therapy to limit risk of tumor re-growth.
For more advanced uveal melanomas, beyond the level that can safely be removed and still maintain vision, eye removal is advised. A microscopic tissue exam is performed to further define tumor type and grade (likelihood of tumor spread).
For melanosis, the prognosis is excellent. There is a change in the appearance of the iris, but there are no risks to systemic health with this condition. Melanomas of the iris have been described to spread to other areas of the body. This is especially true for cats, and unfortunately, early removal of the eye does not always prevent spread of tumor cells. In dogs, most intraocular pigmented tumors do not spread beyond the eye, if diagnosed relatively early.