Ocular Neoplasia in Dogs

Eyelid neoplasms are the most frequent type of ophthalmic neoplasms in dogs. Eyelid masses in dogs are mostly adenomas or adenocarcinomas that arise from the meibomian glands. Both upper and lower eyelids can be affected. Adenomas and adenocarcinomas of the meibomian gland are the most common lid neoplasms (~60%) in older dogs.1 Local irritation necessitates treatment, which is usually successful. Meibomian (sebaceous) adenocarcinomas are locally invasive and demonstrate histologic criteria of malignancy; however, they are not known to metastasize. Surgical excision is usually effective, infrequent recurrence is infrequent. Debulking with adjunctive cryotherapy also leads to good results. Eyelid melanomas, exhibited as pigmented masses on the eyelid margin or a mass within the lid, should be widely excised or treated with debulking and cryotherapy.

Other frequent eyelid neoplasms include histiocytoma, mastocytoma, and papilloma and may require biopsy to determine the best mode of therapy and prognosis. Most canine eyelid neoplasms can be treated successfully by only surgical excision or debulking and adjunctive cryotherapy.

Canine conjunctival neoplasms are reported to have a greater propensity for malignancy and local infiltration than do eyelid neoplasms, and they require more extensive surgical excision and adjunctive treatment. Because recurrence may occur, periodic reexaminations are recommended.

Orbital neoplasms in dogs produce exophthalmos, conjunctival and eyelid swelling, strabismus, and exposure keratitis. The affected globe cannot be retropulsed. Usually, there is no pain upon opening the dog's mouth, as compared to orbital abscess or cellulitis. Because most orbital tumors in dogs are malignant and are not diagnosed until the disease is advanced, the longterm prognosis is often poor. However, early diagnosis and treatment can result in much improved survival rates.2

The most frequently diagnosed tumors include osteosarcomas, fibrosarcomas, and nasal adenocarcinomas. The neoplasm type should be determined histologically, and the extent of the mass determined by physical examination, skull imaging (including special contrast procedures, CT, and MRI), and ultrasonography before treatment by surgical excision or radiation. Excision of the orbital mass with the globe and all orbital tissues (including adjacent bone) may decrease the possibility of recurrence.

Depending on the tumor type, prognosis may be guarded or poor. Surgery, sometimes combined with chemotherapy or radiation therapy, can potentially provide a cure. Early diagnosis and intervention provide the best opportunity for a cure. Depending on the tumor type and location, the mass may be able to be removed while sparing the globe and preserving vision. Early referral to a specialist is recommended.

Corneal and limbal neoplasms are uncommon in dogs and can be confused with nodular fasciitis and proliferative keratoconjunctivitis. Biopsy is often necessary to establish the diagnosis and the specific plan for the best treatment. Limbal or epibulbar malignant melanomas are focal, usually superficial, pigmented masses that extend both onto the cornea and caudally toward the globe’s equator. After close intraocular examination (including gonioscopy and B-scan ultrasonography) to detect possible penetration of the sclera, partial- to full-thickness surgical excision, together with scleral grafts, cryotherapy, or laser photocoagulation, is usually successful. If intraocular extension occurs, enucleation is performed.

Melanomas are the most common primary uveal neoplasm in dogs, are usually pigmented, and most frequently involve the iris and ciliary body, with the latter often being the site of origin. Choroidal melanomas, common in humans, are rare in dogs. Clinical signs of anterior uveal melanomas may include an obvious mass, persistent iridocyclitis, hyphema, glaucoma, and pain. Benign melanomas or melanocytomas (80%) are most common in dogs. Metastatic rates are reported to be 4%–10%.3 Metastasis is infrequent (< 5% of cases). Recent studies of iridal melanomas, especially in young Labrador Retrievers, suggest that noninvasive diode laser photocoagulation may be effective and can be repeated if necessary, thereby avoiding enucleation. For smaller lesions, surgical removal by a specialist is also an option. Ciliary body adenomas and adenocarcinomas are the most frequent epithelial neoplasms of the anterior uvea. Clinical signs may include hyphema, glaucoma, and usually a nonpigmented mass behind the iris and in the pupil. Neoplasms of neuroectodermal origin are rare. Treatment is usually enucleation.

Secondary uveal adenocarcinomas are relatively infrequent in dogs and originate from a number of distant sites. Other neoplasms, such as transmissible venereal tumor and hemangiosarcoma, may metastasize to the anterior uvea. Lymphosarcoma is the most common secondary neoplasm to affect the eye. It frequently involves the anterior uvea and other ocular structures and may present as bilateral disease. Systemic therapy with topical or systemic anti-inflammatory treatment for intraocular lymphoma may be attempted using one of several available lymphoma treatment protocols; however, dogs with both intraocular and systemic lymphoma have shorter survival times.