Ocular Neoplasia in Dogs
Eyelid neoplasms are the most frequent group of ophthalmic neoplasms in dogs. Adenoma and adenocarcinoma of the meibomian gland are the most common lid neoplasms (~60%) in older dogs; local disfigurement and irritation necessitate excision, which is usually successful. Meibomian (sebaceous) adenocarcinomas are locally invasive and histologically malignant but are not known to metastasize. Lid melanomas, exhibited as spreading pigmented masses on the eyelid margin or a mass within the lid, should be widely excised. Other frequent eyelid neoplasms include histiocytoma, mastocytoma, and papilloma and may require biopsy to determine the best mode of therapy and prognosis. The vast majority of canine eyelid neoplasms are treated successfully by only surgical excision.
Canine conjunctival neoplasms have a greater propensity for maligancy and local infiltration than eyelid neoplasms and require more extensive surgical excision. Because recurrence may occur, periodic reexaminations are recommended.
Orbital neoplasms in dogs produce exophthalmia, conjunctival and eyelid swelling, strabismus, and exposure keratitis. The globe cannot be retropulsed. Usually, there is no pain. Because ~90% of the neoplasms are malignant and ~75% arise within the orbit, the prognosis for longterm survival is often poor. 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 radiographs (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 but is more disfiguring, especially in shorthaired dogs. Prognosis is guarded or poor; 25%–40% of affected dogs are euthanized on diagnosis. Surgery, sometimes combined with chemotherapy, can often prolong life for ≥6 mo.
Corneal and limbal neoplasms are uncommon in dogs and can be confused with nodular fasciitis and proliferative keratoconjunctivitis in Collies. Biopsy is often necessary to establish the diagnosis and the specific plan for the best therapy. 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 with scleral grafts, cryotherapy, or laser photocoagulation is usually successful. If intraocular extension occurs, enucleation is performed.
Melanomas are the most common uveal neoplasm, are usually pigmented, and most frequently involve the iris and ciliary body, with the latter being the site of origin. Choroidal melanomas, common in people, are rare in dogs. Clinical signs of anterior uveal melanomas may include an obvious mass, persistent iridocyclitis, hyphema, glaucoma, and pain. These melanomas are divided into melanocytic melanomas (80%–90%) and malignant melanomas (10%–15%). Metastasis is infrequent (<5%). Ciliary body adenoma and adenocarcinoma are the most frequent epithelial neoplasms of the anterior uvea. 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. Recent studies in 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.
Secondary uveal adenocarcinomas are relatively infrequent and originate from a number of distant sites. Other neoplasms, such as transmissible venereal tumor and hemangiosarcoma, may metastasize to the anterior uvea. Lymphosarcoma frequently involves the anterior uvea and other ocular structures and may present as bilateral disease. Systemic therapy with topical and/or systemic anti-inflammatory treatment for intraocular lymphoma may be attempted using one of several available lymphoma protocols (eg, combination of cyclophosphamide, prednisolone, vincristine, and/or doxorubicin), but dogs with both intraocular and systemic lymphoma have shorter survival times.