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Tumors of the Anterior Uvea (Iris and Ciliary Body) in Cats

By: Dr. Noelle McNabb

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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 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 body sites (secondary tumors).

Melanomas are the most common primary uveal tumor. Cats most commonly develop a brown color change that affects much of the iris. This pigmentation of the iris may develop over several months to years and may remain flat rather than forming a mass. Melanomas of the iris may be benign or malignant, and with time, benign tumors may become malignant.

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 any kind of malignant tumor is possible. A rare type of tumor in the cat is the development of a malignant sarcoma within the eye months to years after the eye has experienced some sort of penetrating injury. These sarcomas are highly malignant.

Advanced anterior uveal tumors in many animals lead to symptoms of eye pain and blindness due to the development of uveitis, bleeding within the eye (hyphema), glaucoma, and damage to nearby structures of the eye. Unlike dogs, most anterior uveal tumors in cats tend to be malignant.

What to Watch For

  • A change in color in the iris
  • Obvious nodule or mass in the iris or visible behind the pupil
  • Persistent dilation (enlargement) of the pupil or change in pupil shape
  • Hyphema (bleeding within the anterior chamber of the eye)
  • Cloudiness of the cornea or surface of the eye
  • Signs of pain – squinting, increased tearing, sensitivity to light (photophobia)
  • Possible swelling or a change in the shape of the eye
  • Bloodshot or reddened conjunctiva
  • Swelling of the eye

    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:

  • Lack of energy (lethargy, malaise)
  • Decreased appetite (anorexia)
  • Decreased activity and playfulness, hiding
  • Weight loss

    Diagnosis

    Diagnostic tests for anterior uveal tumors often include:

  • Complete medical history and physical examination

  • Complete ophthalmic examination including testing of pupillary light reflexes, Schirmer tear test, fluorescein staining of the cornea, tonometry to measure the pressure within the eye, and examination of the interior of the eye under magnification. Your veterinarian may refer your cat to a veterinary ophthalmologist for further evaluation using specialized instrumentation.

    If a tumor is suspected or confirmed on the eye examination, then further testing may be warranted and may include the following:

  • Ocular ultrasound
  • Complete blood count
  • Serum biochemistry tests
  • Bone marrow aspirate and cytology
  • Chest X-rays
  • Abdominal X-rays and possibly an ultrasound
  • Computerized tomography (CT) or magnetic resonance imaging (MRI)

    Treatment

    Medical treatment alone is not enough to treat primary anterior uveal tumors. In early stages of uveal lymphosarcoma (a metastatic tumor), chemotherapy may induce tumor regression and remission of the cancer in some animals. Response to medical treatment for all 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.

    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

    Any time the iris changes color or there is eye discomfort, your cat 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 most anterior uveal tumors. Primary tumors and most secondary uveal tumors develop spontaneously. Post-traumatic sarcomas can be prevented by early removal of eyes that have been blinded and deformed by penetrating injuries.

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