By definition, a tumor is an abnormal growth of tissue caused by an uncontrolled progressive proliferation of cells that serve no physiological function. Tumors can be benign or malignant, and can be anywhere on or in the body. Benign tumors are slow growing and usually remain in one spot; malignant tumors grow more quickly and can spread from one area of the body to another.
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Canine Eye Tumors
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Most canine eye tumors are benign, but many lead to secondary glaucoma. Canine eye tumors can also interfere with normal vision. Tumors can occur in the eye, behind the eye, on the surface of the eye or on the eyelid. Many tumors can be surgically removed; however, enucleation (removal of the eye) is recommended with some malignant tumors or when glaucoma is present.
Surgical Treatment
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Sector iridectomy is the surgical removal of a large section of the iris. This surgery is common in the treatment of glaucoma and melanomas.
Diode laser ablation uses a special laser to burn away the tumor. This is common as a treatment for adenomas and adenocarcinomas of the ciliary body and uveal melanoma.
Enucleation is the surgical removal of the eye. Simple enucleation involves just the eye; complex enucleation involves the removal of the surrounding muscles and tissues of the orbital cavity.
Intraoccular Tumors
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Uveal melanoma is the most common tumor affecting dogs' eyes. These are usually benign, slow growing tumors with dark pigment. They are usually very large before they are noticed due to the dark color of the iris. If the tumor is in the ciliary body, glaucoma is usually present before the tumor is diagnosed. Sector iridectomey is performed for large tumors. Diode laser ablation is used for small tumors and may actually kill off tumor cells and cause an immune response to the tumor.
Adenomas and adenocarcinomas of the ciliary body are the second most common tumor occurring in the eye. These are pink or red masses seen in the pupil. Most of these are benign and rarely spread, however, they can lead to glaucoma. Surgical removal of the tumor is possible but if glaucoma is present, enucleation is recommended.
Orbital Tumors
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Tumors in the orbital area of the eye are relatively common. Although primary tumors can occur, the vast majority are caused by metastatic disease or extensions of surrounding tumors. Diagnosing these tumors is difficult due to the location; an ultrasound or biopsy is usually necessary. Most orbital tumors are discovered late in the course of the disease; therefore, prognosis, even with surgical treatment, is poor.
Eyelid/Lachrymal Gland Tumors
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The most common tumor of the eyelid is meibomian adenoma. These tumors originate in the sebaceous glands of the eyelid. Meibomian adenoma is slow growing benign tumors that sometimes bleed. These tumors can cause irritation to the cornea due to rubbing or by releasing inflammatory lipids. Surgical removal is usually successful as long as the entire tumor is removed.
Lachrymal gland (tear duct) tumors are a common type of tumor originating around the eye. Lachrymal gland tumors are usually malignant (adenocarcinomas), difficult to remove and spread easily into surrounding tissue. These tumors will recur if they are not completely removed. Although these tumors rarely metastasize, the prognosis is poor due to their invasive nature and difficulty of complete removal.
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