Page 1291 - Problem-Based Feline Medicine

62 – THE CAT WITH ABNORMAL PUPIL SIZE, SHAPE OR RESPONSE 1283

such as carbimazole or methimazole. For more details Signs of anterior uveitis such as flare, hyperemia of
see main reference on page 305 (The Cat With Weight the iris surface, keratic precipitates, and/or fibrin.
Loss and a Good Appetite).

INFECTIOUS CHORIORETINITIS**
Diagnosis
Diagnosis is based initially on the identification of sus-
ANTERIOR UVEITIS** (PROTOZOAL,
FUNGAL OR PARASITIC) (TOXOPLASMA, picious signs on careful examination of the fundus and
CRYPTOCOCCUS NEOFORMANS, the anterior segment.
BLASTOMYCOSIS, COCCIDIOIDOMYCOSIS, Diagnosis is confirmed by serology, or identification
HISTOPLASMA CAPSULATUM, of the characteristic morphology of a pathogen from the
OPHTHALMOMYIASIS) subretinal exudate or anterior chamber fluid, or from
another site such as lymph node, bone marrow, liver or
Classical signs lung aspirate.
● Technique of anterior chamber aqueous cen-
● Abnormal pupil light reflexes.
tesis: Prepare the eye using a 1:20 Povidine solu-
● Variable degrees of vision loss.
tion. Under sedation using topical anesthesia and
● Variable signs on fundoscopy including
using illumination and magnification, pass a 30-G
retinal detachments, retinal hemorrhages, needle obliquely into the anterior chamber. It
subretinal exudates, subretinal is important to visualize the needle passing into
granulomas, pre-retinal hemorrhages.
● Signs of anterior uveitis. the anterior chamber anterior to the iris. Drain
1
approximately ⁄2 a needle hub, then withdraw the
needle.
For more details see main reference on page 1300 (The
● Technique of subretinal fluid centesis: Under
Cat With Abnormal Iris Appearance) or page 1172
general anesthesia, prepare the conjunctival sur-
(The Blind Cat or Cat With Retinal Disease).
faces with 1:20 Povidone iodine and with the pupil
dilated (if possible), rotate the globe ventrally and
Clinical signs
immobilize with Colibri forceps. Insert a 27-G
Organisms that may produce signs of chorioretinitis or needle perpendicularly, and if possible, visualize
uveitis include protozoa (Toxoplasma gondii), fungi the needle passing through the sclera and choroid
(Cryptococcus neoformans, blastomycosis, histoplas- into the subretinal space, and aspirate 0.1–0.2 ml of
mosis, coccidioidomycosis), parasites (ophthalmo- fluid.
myiasis (fly larval migration)).
Many infectious agents may not actually be present
Systemic clinical signs of fever, dyspnea, gastrointesti- within the eye to cause ocular disease, but cause
nal disease, upper respiratory disease or other organ pathology by the presence of immunocompetent
involvement suggest infection with Toxoplasma or any cells within the uveal tissue, which have been stimu-
of the systemic fungal diseases. lated by antigens in sites remote from the eye.
Toxoplasma gondii is thought to cause uveitis in this
Abnormal pupil responses occur due to retinopathy or
way.
to central nervous system involvement.
An important differential diagnosis is hypertensive
Variable degrees of vision loss result, depending on
retinopathy. This is usually a very acute disease occur-
degree of retinal or central nervous tissue injury.
ring mainly in old cats, which have other signs such as
Variable signs on fundoscopy including retinal detach- weight loss, and renal or cardiac disease. It is not asso-
ments, retinal hemorrhages, subretinal exudates, sub- ciated with anterior uveitis, and is not usually asso-
retinal granulomas, and pre-retinal hemorrhages ciated with other CNS signs, although seizures may
consistent with chorioretinitis. occur.