Uveal Melanoma in Dogs
The uvea is the part of the eye that is made up of the iris (the colored part of the eye surrounding the pupil), the ciliary body (which produces the fluid within the eye [aqueous humour] and controls the ciliary muscle contractions that aid in near focus), the choroid (which provides oxygen and nourishment to the retina – the inner surface of the eye), and the pars plana (at the front of the eye, where the iris and sclera [white of the eye] touch). A melanoma is clinically characterized by malignant growth of melanocytes, cells that are dark in appearance due to the inclusion of the melanin pigment.
Uveal melanomas usually arise from the front of the iris’ surface, with extension to the ciliary body and choroid. These tumors tend to be flat and diffuse, not nodular (unlike intraocular melanomas, which are raised masses). Such tumors initially have a benign (non-spreading) clinical and cellular appearance. Uveal melanomas are the most common primary intraocular neoplasm in dogs. They are usually benign and unilateral, affecting the anterior uvea most often. However, uveal melanomas are just as often capable of destroying the eye. Anterior uveal melanomas have a four percent rate of cancerous spread through the bloodstream to the lungs and visceral organs. Choroidal melanomas rarely metastasize.
Symptoms and Types
Anterior Uveal Melanoma
- Pigmented scleral (white part of the eye) or corneal (the transparent front part of the eye) mass
- Pigmented mass visible
- Irregular pupil
- Inflammation of the eye (the uvea)
- Glaucoma (Increased pressure in the eyes)
- Hyphema (Blood in the eye)
- No vision loss unless mass obstructs the pupil or glaucoma has developed
- Often missed because of tumor location
- Mass farther back in the eye
- Very slow-growing; rarely requires removing the eye
- Rare tumor
- Flat, pigmented iris freckles have potential to transform into melanomas
- There is a presumed autosomal (non-sex-linked) recessive inheritance in Labrador retrievers
Your veterinarian will perform a thorough physical exam on your dog, including a complete ophthalmic exam (including testing pressure within the eye and proper drainage of the eye’s aqueous humor). A complete blood profile will also be conducted, including a chemical blood profile, a complete blood count, a urinalysis and an electrolyte panel. Evidence of metastasis may may be present in the blood profile, or the blood count may show increased white blood cells, which can be indicative of the body's immune system fighting the malignant cell growth. You will need to give a thorough history of your dog's health and onset of symptoms.
X-rays and an ultrasound may also help to determine the extent of metastatic disease in the eye. During the ophthalmic exam, tonometry will be used to measure the pressure in the eyes, and gonioscopy will be used to see if the melanoma has spread to the drainage angle. Slit-lamp biomicroscopy can be used to gage the size and location of the mass. The mass should be transilluminated, a technique which uses strong light to shine through the eyeball, illuminating it throughout as an aid to diagnosis. Indirect ophthalmoscopy can also be used to investigate the eye, with or without concomitant scleral indentation.
The layer of the eye that is charged with receiving and processing images
Anything having to do with the eye or care of the eye
The outer layer of the eye that helps it to keep its round shape; the eye white.
A condition of having only one side
Anything pertaining to an organ
The term used to refer to the part of the eye containing the iris, the cilia, and the choroid.
An in-depth examination of the properties of urine; used to determine the presence or absence of illness
The term for the dark pigment in the cells of skin and hair
The condition of being drowsy, listless, or weak
A disorder that has resulted from intraocular pressure
The removal of a whole organ; usually the eye ball
Not being able to cause harm; the opposite of malignant.
Term used to refer to the liquid that gives nourishment to the structures inside the rear segment of an animal's eye.
A nonliving substance in a cell
Transmitting genes from parent to child
In veterinary terms, used to refer to the front of the body.
The colored layer around the pupil
Found inside the eye
Something that becomes worse or life threatening as it spreads