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Overview of Canine Tumors of the Anterior Uvea
The uvea in the eye consists of three parts: the iris, which is the colored portion of the eye behind the cornea; the ciliary body, which is the tissue immediately behind the iris lying between the iris and the choroid; and the choroid, which is the vascular layer in the back of the eye that supplies nutrition to the dog’s retina. The iris and ciliary body make up the anterior uvea and the choroid is called the posterior uvea.
Tumors occurring in the anterior uvea involve the iris, ciliary body, or both tissues. They may originate from cells within these tissues (primary tumors) or they may spread to the eye from other sites (secondary tumors).
Melanomas are the most common primary uveal tumor. In dogs, melanomas usually appear as dark brown (pigmented), raised nodules within the iris and ciliary body. Some melanomas of the iris are benign and remain confined to an area of the iris and slowly enlarge. Some melanomas of the ciliary body are benign, but gradually enlarge and do damage to nearby tissues in the eye. Other melanomas of the iris and ciliary body are malignant and spread not only within the eye, but may also extend into the tissues around the eye, to the brain and to other organs such as lymph nodes and the liver.
Other primary tumors include the a benign tumor of the ciliary body (ciliary body adenoma), a malignant tumor of the ciliary body (adenocarcinoma), and a tumor that arises from embryonic tissues of the eye (medulloepithelioma).
The most common secondary anterior uveal tumor is lymphosarcoma. Metastasis to the anterior uvea from malignant tumors of other body organs is also possible.
Advanced anterior uveal tumors in many animals cause eye pain and blindness from inflammation (uveitis), bleeding within the eye (hyphema), elevations in pressure within the eye (glaucoma), and damage to nearby structures of the eye.
What to Watch For
Physical symptoms of illness may be seen with secondary (metastatic) uveal tumors because these tumors originate in other body organs and are usually present in that organ for some time before they spread to the eye. Systemic signs that may be seen include:
Diagnosis of Anterior Uvea Tumors in Dogs
Diagnostic tests for anterior uveal tumors often include:
If a tumor is suspected or confirmed on the eye examination, then further testing may be warranted and may include the following:
Treatment of Anterior Uvea Tumors in Dogs
Medical treatment alone is not enough to treat most anterior uveal tumors. Chemotherapy may be used for lymphosarcoma. Response to medical treatment for all primary and other secondary uveal tumors is generally poor.
The treatment of choice for most uveal tumors is removal of the eye (enucleation). Malignant tumors must be removed as soon as possible to prevent their spread to other tissues. Large benign tumors often cause damage to nearby structures, as well as glaucoma, and the eye generally needs to be removed.
Occasionally some benign iris tumors are discovered while they are still small. Surgical removal of the mass can be attempted by surgical excision of the affected portion of the iris (iridectomy). Laser treatment using Nd-YAG or diode lasers may also be performed on very small anterior uveal tumors that are dark in color. Lasering is less effective when the tumor is white, cream-colored or pink.
One complicating factor is that it is not often possible to determine if the uveal tumor is benign or malignant just by its appearance. There are also no effective biopsy techniques that can be used for these tumors. The tumor may only be determined to be benign/malignant once the eye is removed and a thorough pathological examination has been performed. For this reason, it is often necessary to remove the eye just to play it safe in case the tumor is malignant.
Prior to removal of the eye, it is important to determine that other organs in the body are free of tumor. With the exception of lymphosarcoma, if there is evidence of tumor(s) in other areas of the body, then no treatment may be effective and euthanasia may need to be considered.
Home Care and Prevention for Anterior Uvea Tumors in Dogs
Any time the iris changes color or there is eye discomfort, your dog should be examined by your veterinarian. For surgical or medical treatment to offer the most successful outcome, time is of the essence.
There is no preventive therapy or care for anterior uveal tumors. Primary tumors and most secondary uveal tumors develop spontaneously.
Information In-depth for Anterior Uvea Tumors in Dogs
The most common primary anterior uveal tumors include melanoma of the iris or ciliary body, and adenomas or adenocarcinomas of the ciliary body.
Melanomas are the most common primary uveal tumor. In dogs, iris melanomas typically appear as dark-brown (pigmented) raised nodules within the iris itself. Ciliary body melanomas may appear as a brown mass within or behind the pupil, or as a brown spot that develops within the white of the eye.
Melanomas may be benign and may remain confined to a localized area of the iris and slowly enlarge. Benign ciliary body melanomas gradually enlarge and disturb nearby structures within the eye. Malignant melanomas tend to spread extensively through the eye. They alter the shape and thickness of the iris, distort the pupil, may grow towards the back of the eye, may partially dislocate the lens, and may extend through the sclera (white covering of the eye). Glaucoma may also develop.
Some melanomas lack the typical brown/black pigmentation and are pink/white in color. These are called amelanotic melanomas. All amelanotic melanomas are considered malignant.
All anterior uveal melanomas have malignant potential. However, in the dog most anterior uveal melanomas are benign when they develop in middle-aged to older dogs (8 to 10 years). In contrast, uveal melanomas that develop in dogs less than four years old tend to be malignant and more likely to expand rapidly within the eye. Darkly pigmented dog breeds, specifically the German shepherd, Labrador retriever, Weimaraner and boxer have a higher risk for developing uveal melanomas.
The most common secondary anterior uveal tumor is lymphosarcoma. Usually the lymphosarcoma in the eye is one component of widespread cancer through the body. It is rare for lymphosarcoma to appear only in the eye alone. Other uveal tumors represent the spread of malignant tumors from some other location in the body, and these include metastatic mammary carcinoma, renal carcinoma, hemangiosarcoma, transmissible venereal tumor, and malignant melanoma of the skin or oral cavity. Metastasis to the anterior uvea from any kind of malignant tumor is possible, although most metastatic tumors appear in the choroid rather than in the anterior uvea.
Some other ophthalmic diseases or conditions can mimic the signs that develop with anterior uveal tumors. It is important to exclude these conditions before establishing a conclusive diagnosis.
Veterinary care includes a variety of diagnostic tests and subsequent treatment recommendations, as outlined below.
Diagnostic tests are performed to determine if the anterior uveal tumor is confined to the eye or if other organs or body cavities are affected with tumor. The results of these tests help define what is the most appropriate treatment. These tests may include:
Treatment In-depth for Anterior Uvea Tumors in Dogs
Treatment of anterior uveal tumors may be divided into either medical management or surgical therapy. Eyes with primary uveal tumors that are amenable to complete surgical excision may require medical therapy following surgery. In the early stages of uveal tumor development, clinical evidence of eye discomfort or irritation is often not evident. Invariably, as uveal tumors enlarge, they result in inflammation (uveitis) and secondary glaucoma, and the eye may become painful.
Medical treatment alone is not enough to treat primary anterior uveal tumors. Typically, the inflammation caused by the tumor expansion within the eye does not respond well to medical therapy.
In early stages of uveal lymphosarcoma (a metastatic or secondary tumor), chemotherapy may induce regression of the tumor and the dog may go into remission. However, eyes that develop secondary glaucoma from advanced lymphosarcoma may not respond as well to chemotherapy and may remain painful and blind.
Response to medical treatment for all other secondary uveal tumors is generally poor and ultimately most of these tumors require that the eye be surgically removed (enucleated).
For small iris tumors, the tumor and part of the iris (iridectomy) may sometimes be removed surgically. Some darkly colored tumors may also be treated with a diode or Nd-YAG laser. Both of these procedures have some potential serious side effects and are applicable to only a small number of iris tumors.
Most anterior uveal tumors are too large and extensive to remove surgically, so removal of the eye is usually necessary. Quite often these eyes are painful due to secondary glaucoma, uveitis, or hyphema.
Home Care of Dogs with Anterior Uvea Tumors
Optimal treatment for your pet requires a combination of home and professional care. Follow-up can be critical, especially if your pet does not improve rapidly.