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

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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.

    • A focal spot of brown pigmentation on the iris of a cat that is flat and freckled-like in appearance. This is commonly referred to as a nevus and is not a tumor.

    • Anterior uveal melanoma in a cat with a previously blue iris. The tumor has resulted in iris thickening and patchy pigmentation causing distortion of the pupil shape.

    The most common primary anterior uveal tumors include melanoma of the iris and ciliary body, and adenomas or adenocarcinomas of the ciliary body.

    Melanomas are the most common primary uveal tumor. Cats most commonly develop a diffuse, flat melanoma of the iris that begins as progressive pigmentation (darkening) of the surface of the iris. This color change is often a slow process and may develop over several months to years. Several golden-brown pigmented spots or "freckles" may develop simultaneously on the iris that progressively enlarge, grow together and become irregular along their surfaces. The migration of cancerous pigmented cells (melanocytes) into the iris eventually causes the iris to thicken and the shape of the pupil may become distorted. The pupil often remains larger than the opposite normal pupil. 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. Metastatic disease related to uveal melanoma is more commonly observed in the cat than in the dog. Metastasis may occur as late as one to three years after eye removal and usually involves the lymph nodes, lungs and liver.

    Primary sarcomas of the eye may develop in cats months to years after an event of ocular trauma or injury. These tumors are highly malignant and necessitate immediate removal of the eye.

    The most common secondary anterior uveal tumor is lymphosarcoma. Usually the lymphosarcoma in the eye is one component of widespread cancer throughout the body. It is rare for lymphosarcoma to appear in the eye alone. Other uveal tumors represent the spread of malignant tumors from some other location in the body, such as breast cancer, cancer of the kidney or cancer of the thyroid. 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.

    A few other ophthalmic diseases or conditions can mimic the symptoms similar to those observed with anterior uveal tumors. It is important to exclude these conditions before establishing a conclusive diagnosis.

  • Severe uveitis
  • Traumatic injuries to the eye
  • Chronic anterior uveitis with hyperpigmentation of the iris
  • Iris cysts
  • Glaucoma
  • Conjunctival and scleral tumors
  • Conjunctival and scleral inflammatory masses that look like tumors
  • Old bleeding into the anterior chamber of the eye

  • Veterinary care includes diagnostic tests and subsequent treatment recommendations, as outlined below:

    Diagnosis In-depth

    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:

  • A complete history and thorough physical examination, including palpation for enlarged lymph nodes, and swollen, enlarged or irregularly shaped abdominal organs. Your veterinarian will listen to the chest with a stethoscope to help determine whether the heart and lung sounds are normal. When tumors or fluid accumulate in the chest, these sounds are often muffled.

  • 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.

  • Gonioscopy, a specialized test to examine the area in the front of the eye where fluid leaves the eye. This helps to determine if the uveal tumor is extending into and/or obstructing this drainage angle.

  • Ocular ultrasound to delineate the boundaries of the intraocular tumor. It is also useful to determine if retinal detachment or lens displacement has occurred and may help to determine if the tumor extends behind the eye.

  • Aqueocentesis (fluid sample taken from the anterior chamber of the eye) and fine-needle aspirate of the uveal mass may be useful in distinguishing certain infections (fungal, protozoal, parasitic) from a cancerous process.

  • Routine blood work (complete blood count, serum biochemistry) and urinalysis are usually done to assess the function of other organs.

  • Feline leukemia virus (FeLV) testing is often done as FeLV-positive cats are at an increased risk for developing cancer, especially lymphosarcoma.

  • Bone marrow aspirate and cytology may be done if lymphosarcoma or other bone marrow cancers are suspected.

  • Chest X-rays are usually taken to search for masses or tumors, enlarged lymph nodes, and fluid in the chest.

  • Abdominal X-rays may be taken to search for organ enlargement, masses and enlarged lymph nodes in the abdomen. These X-rays may be followed by an abdominal ultrasound if any abnormalities are discovered.

  • Computerized tomography (CT) or magnetic resonance imaging (MRI) may be used to examine the eye, orbit, optic nerve and brain. These tests are most useful if extension of the uveal tumor into the orbit or brain is suspected.

    Treatment In-depth

    Treatment of anterior uveal tumors may be divided into either medical management or surgical therapy. Most anterior uveal tumors in the cat are not treatable with medical therapy and require surgery to remove the eye.

    Medical Management

    Medical treatment alone is usually 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 the early stages of uveal lymphosarcoma, chemotherapy may induce regression of the tumor and the cat 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.

    Surgical Management

    Enucleation is the most common therapy for many anterior uveal tumors in the cat. Often these eyes are painful due to secondary glaucoma, uveitis or hyphema.        

  • 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.

  • Administer all prescribed medication as directed. Alert your veterinarian if you are experiencing problems treating your pet.

  • Intraocular surgery or laser treatment of uveal tumors always results in significant inflammation within the eye. This inflammation requires intensive medical treatment, and frequent follow-up examinations are necessary for several weeks after surgery.

  • Periodic ocular ultrasound examinations may be necessary to monitor for any evidence of tumor regrowth.

  • The risk of recurrence or regrowth of primary uveal tumors after surgical removal is possible for all malignant tumors and for all benign tumors that are incompletely removed. The prognosis for vision and survival of the eye depends upon the type of tumor, whether chemotherapy is effective for the specific tumor type, whether the entire tumor was excised during surgery, and whether the tumor is present anywhere else in the body.

  • It is best to remove eyes with primary uveal tumors that are extensive or that result in secondary glaucoma in order to extend the lifespan of the pet and reduce the risk of metastasis. Follow-up examinations after removal are minimal for the surgery site and focus mainly on monitoring for any evidence of metastasis.

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