Page 1306 - Problem-Based Feline Medicine

1298 PART 15 CAT WITH EYE PROBLEMS

Diffuse iris melanoma arises as a primary neoplasia of Diagnosis
the iris stroma, and is the most common primary intra-
Diagnosis is based initially on the appearance of the iris
ocular neoplasm seen in cats.
and consideration of the history.
Lymphosarcoma results from invasion of neoplastic
Amelanotic diffuse iris melanomas are difficult to diag-
lymphocytes from the peripheral circulation.
nose unless the effects of the tumor on angle obstruc-
Intra-ocular sarcoma usually occurs as a sequel after tion and resultant glaucoma are observed.
(usually years) trauma causing penetrating injury to the
Definitive diagnosis may be obtained by fine-needle
lens. It is believed that the sarcoma arises from trans-
aspirate biopsies or anterior chamber centesis and
formed lens epithelium. This neoplasm forms solid
cytology.
masses within the eye, which metastasize rapidly, usu-
ally via the optic nerve.
Differential diagnosis
Ciliary body tumors may represent primary neoplasia
or metastatic neoplasia from an extra-ocular site. Diffuse iris melanoma needs to be differentiated from
other causes of pigmentation of the iris and can look
similar to:
Clinical signs ● A benign pigmented nevus, which appears as a flat
pigment spot in the iris. A nevus will be observed not
Diffuse iris melanoma typically appears as an to have changed in size with serial examination.
enlarging area over months to years of light tan to ● Post-inflammatory pigmentation. A detailed history
dark brown pigmentation on the iris surface. Usually may reveal previous bouts of anterior uveitis within the
the neoplasm does not form an obvious discrete eye. This pigmentation will not be progressive.
mass, but the iris may become diffusely thickened.
The disease is usually unilateral and typically occurs
Treatment
in older cats.
● Presentation may more resemble uveal inflamma- Enucleation of an eye with diffuse iris melanoma is
tion than neoplasia. recommended if:
● Sometimes the disease may present in an advanced ● There is evidence of rapid spread of a diffuse iris
state with secondary glaucoma. melanoma. The eye should be reassessed frequently
● Amelanotic diffuse iris melanomas have also been to determine if the pigmentary change is progressive.
reported. ● Pigmentary change is seen near or in the irido-
corneal angle on gonioscopy.
Lymphosarcoma and post-traumatic sarcoma
● A change in pupil shape or mobility occurs.
more commonly form discrete masses within the eye.
● Secondary glaucoma develops.
Lymphosarcoma often presents as bilateral iris
swelling, and anterior chamber hemorrhage in a young Evidence of metastasis may still occur as late as 2–3
cat, with or without other signs suggesting multicentric years after enucleation.
neoplasia.
If there is a high suspicion or confirmation of an intra-
Ciliary body adenoma is a rare, slow-growing neo- ocular sarcoma it requires immediate enucleation
plasm, which appears as a whitish to cream mass behind with exenteration of orbital tissue. Prognosis is still
the pupil margin. guarded and most cats will eventually die from
metastatic disease within months.
Metastatic neoplasia from an extra-ocular primary
tumor appears as an intra-ocular neoplasm involving Systemic chemotherapy for lymphosarcoma can be
the iris, and is associated with a similar neoplasm attempted unless the eye is already affected by secondary
remote from the eye, e.g. mammary or uterine adeno- glaucoma. For more detail see main reference on page 432
carcinoma. (The Yellow Cat or Cat With Elevated Liver Enzymes).