A localized area of increased pigmentation is called an iris melanoma. This term means a tumor or growth of pigmented (melanin-containing) tissue. These are seen mostly frequently in cats, especially older cats, and less frequently in dogs. These are also known as "iris nevus", "iris freckle" and "melanosis." Melanosis just means pigmentation of tissue
These tumors are located on or within the iris. The iris is the colored portion of the eye which we see when we look at each other and at our pets. These lesions are most commonly seen in cats due to the iris color which is common in cats. In dogs, the iris is usually light to medium brown. In cats, the iris is either gold, yellow, blue or green. For this reason, a brown growth is seen earlier in cats.
Melanomas of the iris can look like single or multiple flat dark spots (called iris nevus if singular or nevi if multiple), or as if the color of the entire iris has changed to a dark brown.
The black arrow indicates an early darkening of the iris in this cat. An early pigmented iris lesion (iris melanoma) is present.
The white arrow indicates a more diffuse pigmented iris lesion (iris melanoma).
More numerous pigmented iris lesions in this cat.
Alternatively, there may be single or multiple dark, raised masses of the iris.
The dark arrow indicates a raised, dark tumor of the iris (iris melanoma). This eye was removed and the pathological diagnosis was a malignant lesion.
A raised focal iris mass which had a roughened appearance when examined. This mass was lasered successfully. The exact type of tumor was not determined.
Traditionally, when the masses are flat and either single or multiple, they are referred to as benign iris melanoma(s). When they are raised, they are considered to be malignant. These definitions are not always correct.
Just that! Understand, just by looking at the lesion of the iris, NO ONE can tell exactly what a lesion is. Removing the eye or the lesion and performing pathology is the only way to know for sure what a lesion is. A pathologist can determine what a tissue is by microscopic examination of tiny pieces of the mass. When a Veterinary Ophthalmologist examines a patient using a slit-lamp biomicroscope, we can see what the lesion looks like grossly. Based on the experience of the Ophthalmologist, an educated guess can be made. Without removing the lesion, no one will know exactly what it is. There are techniques of using a syringe and small needle to "vacuum" cells off the lesion in an attempt to make a diagnosis. Unfortunately, within any tumor, cell types vary and what is on the surface of the iris isn¹t always what¹s down deep inside the mass.
What should be done for any one individual patient should be based upon the age of the pet, the overall health of the pet, any intraocular (within the eye) complications and the extent of the tumor. Currently a controversy exists in veterinary ophthalmology about the best way to deal with these lesions. Veterinary pathologists who deal primarily with ophthalmic tissue examination recommend that ANY iris melanoma lesion should be cause for removal of the eye. Their rationale for this is that they have seen numerous cases where the tumors have spread (metastasized) outside the eye. In several cases, the patients have died from the tumor spreading through the body. Many Veterinary Ophthalmologists have seen patients, especially cats, who have had these lesions for years and eventually died from other causes, such as kidney failure. Because of these cases, most but not all Veterinary Ophthalmologists recommend when the patient has diffuse melanosis of the iris only observation be performed on a semi-annual basis. Once signs of glaucoma or uveitis occurs, then enucleation be performed because to these conditions. Alternatively, if the lesion is solitary, it is possible to either open the eye and remove the melanosis and submit it for the pathologist to examine or to use a laser to destroy the tumor. The advantage of the surgical removal of the melanosis is that you can determine the exact type of tumor it is. The disadvantage of this is that the eye must be opened, bleeding can and will usually occur and it is only feasible to perform on small lesions. The advantage of the laser procedure is that the eye doesn't have to be opened, it can be repeated to remove additional tumors or repeat on the original tumor and that the postoperative period and treatment is much less than with the surgical procedure. The disadvantage of the lasering is that the type of tumor cannot be determined for certain. BUT, it the tumor is gone, and it is early in the course of the condition, then the type of tumor isn't really as important as it might be if the tumor is large.
Have any questions on this subject? Contact
Dennis Hacker via E-mail:
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