Sometimes in dogs primary tumors can develop in and around the various eye tissues and supporting structures. These areas can also be the site of spreading tumors and tumor cells.
Eyelid tumors are the most common group of eye tumors seen in canines. The most common lid tumors are of the meibomian glands in the eyelid and include adenocarcinomas, which are malignant, and adenomas, which are benign. These tumors can be disfiguring and irritating to the dog and are usually successfully removed through surgery. Although adenocarcinomas are invasive and harmful, they aren’t known to spread elsewhere in the eye or body. Spreading masses of color on the edges of the eyelid known as lid melanomas are also removed through surgery. Papilloma, mastocytoma, and histiocytoma are also frequently seen eyelid tumors.
Orbital tumors are those which cause the dog’s eyeball to actually protrude forward, which produces eyelid, cornea, and conjunctiva swelling. Sometimes these tumors cause the eye to be unable to move in synchronization with the other eye, and the eyeball cannot simply be pushed back. Most of the time dogs will not feel any pain when they have orbital tumors. But longterm survival is usually poor seeing as the vast majority of these tumors are malignant – about 90 percent. Additionally, two thirds of these tumors actually arise within the orbit. Veterinarians will use ultrasounds, x-rays, and physical exams to determine what type of tumor the dog has and how large the mass is before surgery or radiation is done. The possibility of tumor recurrence may be diminished by removing the orbital mass, the eyeball, and all orbital tissue nearby, including bone.
Another type of eye tumor that can appear in dogs is a tumor of the cornea, including tumors along the edge of the cornea. However, these tumors are very rare in dogs. Another condition most often seen in Collies called nodular fasciitis, which are rapidly growing benign cells, is often confused with corneal tumors. Keratoconjunctivities, or inflammation of the conjunctiva and cornea, is another condition common in Collies that is often confused with corneal tumors, as well. If melanomas and malignant tumors do occur at the edge of the cornea they are usually very superficial, and surgery is usually successful in these cases. However, once melanomas spread into the actual eyeball, the entire eye must be removed.
If malignant melanomas occur in the eyes of dogs, however, they are usually tumors of the uvea. These masses are black and are typically seen in the tissue and muscle surrounding the lens, as well as in the iris. Persistent inflammation of the iris or of the muscle and tissues surrounding the lens is a common symptom of these types of tumors. Other symptoms include an obvious mass, glaucoma, or high pressure within the eye, rupturing blood vessels within the anterior eye chamber, and general pain. Adenocarcinoma and adenoma of the tissue and muscles surrounding the lens are the most commonly observed tumors of the uvea’s outer layer. Rupturing blood vessels in the anterior eye chamber, a white or pink mass in the pupil and behind the iris, and glaucoma are typical symptoms of these tumors. Removal of the entire eye is usually necessary to treat these tumors. However, some studies have shown that using noninvasive lasers to treat melanomas of the iris may be successful and may be used repetitively if necessary. This treatment has been shown to be especially helpful to Labrador Retrievers. Usually adenocarcinomas that arise in other places of the body do not spread to the uvea.
Venereal tumors, hemangiosarcomas, and other tumors in the body, however, may spread to the anterior uvea. Tumors and cancers such as lymphosarcoma frequently travel to the anterior uvea and affect other eye structures, as well, and may even affect both eyes. Topical, whole-body anti-inflammatory drugs, and other lymphoma treatments can be attempted within the eye using a standard treatment plan. However, canines who develop lymphoma within the eye are usually not given long life expectancies.