The different tissues of the eye and associated structures can develop primary tumors or can be the site of spreading tumor cells.
Eyelid tumors are the most frequent group of eye tumors in dogs. Adenoma (a benign tumor) and adenocarcinoma (a malignant tumor) of the meibomian glands in the eyelid are the most common lid tumors. Because these tumors tend to be disfiguring as well as irritating to the dog, they are usually surgically removed—a process that is usually successful. Adenocarcinomas of the eyelid glands are locally invasive and harmful but are not known to spread elsewhere throughout the body. Lid melanomas, seen as spreading colored masses on the eyelid, are usually surgically removed. Other frequent eyelid tumors include histiocytoma, mastocytoma, and papilloma. Your veterinarian will take a biopsy of the tumor to determine the best treatment and likely outcome. Most eyelid tumors will require surgery.
Tumors in the conjunctiva of dogs are likely to grow more quickly than eyelid tumors, and they have a tendency to destroy the surrounding tissue and spread to other sites. They typically require more extensive surgery to remove. After surgery, dogs should be rechecked regularly because these tumors may regrow.
Orbital tumors in dogs cause the eyeball to protrude forward and produce swelling of the conjunctiva, cornea, and eyelid. They also cause the affected eye to be unable to move in tandem with the other eye. The eyeball cannot be pushed back. Usually, there is no pain. The longterm survival in affected dogs is often poor, because about 90% of these tumors are malignant and about 75% arise within the orbit. A veterinarian will determine the type of tumor and the extent of the mass through physical examination, skull x-rays, and ultrasonography before surgical removal or radiation of the tumor. Computed tomography (CT scan) or magnetic resonance imaging (MRI) may also be necessary to fully determine the extent of the tumor. Surgically removing the orbital mass with the eyeball and all orbital tissues (including nearby bone) may decrease the possibility of recurrence, but the procedure will significantly change the appearance of your dog. Using chemotherapy in addition to surgery may help prolong survival time by 6 months or more.
Tumors of the cornea and those at the edge of the cornea are uncommon in dogs and can be confused with nodular fasciitis (benign cells that grow rapidly into a bumpy mass) and proliferative keratoconjunctivitis (inflammation of the cornea and conjunctiva) in Collies. A biopsy is necessary to tell if it is one of these types of masses or a tumor and to establish a treatment plan. Malignant melanomas at the edge of the cornea are usually superficial, in which case surgical removal is usually successful. If the tumor has penetrated into the eyeball, the eyeball must be removed.
Melanomas are the most common tumors of the uvea. They are usually black and most frequently involve the iris and the tissue and muscle that surround the lens. Signs of tumors of the uvea may include an obvious mass, persistent inflammation of the iris and the tissue that surrounds the lens (anterior uveitis), blood vessel ruptures within the anterior chamber of the eye, glaucoma (high pressure within the eye), and pain. Fortunately, these types of melanomas do not often spread to other parts of the body. Adenoma and adenocarcinoma of the tissue and muscle that surround the lens are the most frequent tumors of the outer layer of the uvea. Signs may include blood vessel ruptures within the anterior chamber of the eye, glaucoma, and usually a white to pink mass behind the iris and in the pupil. Treatment is usually removal of the eyeball. Recent studies in melanomas of the iris, especially in Labrador Retrievers, suggest noninvasive laser surgery may be effective and can be repeated if necessary. Adenocarcinomas from other sites in the body do not commonly spread to the uvea.
Other tumors, such as a venereal tumor and hemangiosarcoma, may spread to the anterior uvea. Lymphosarcoma frequently involves the anterior uvea and other eye structures, and may occur in both eyes. Therapy with topical and/or whole-body anti-inflammatory treatment for lymphoma within the eye may be attempted using one of several standard treatment plans, but dogs with lymphoma within the eye often have short survival times.
Also see professional content regarding cancers and tumors of the eye in dogs.