Page 1190 - Problem-Based Feline Medicine

1182 PART 15 CAT WITH EYE PROBLEMS

There are five stages of the disease described on clini-
FLY LARVAL MIGRATION
cal ophthalmoscopy:
(OPHTHALMOMYIASIS)
● Stage 1. There is an increased granularity of the
area centralis, adjacent to the optic disc. Cats are
Classical signs
visual at this stage.
● Stage 2. The area centralis develops an ellipsoidal ● Vision loss, usually unilateral.
hyper-reflective appearance. Vision is starting to ● Cloudy posterior segment with linear
deteriorate. track-like lesions on fundoscopy.
● Stage 3. A second hyper-reflective lesion develops ● Anterior uveitis associated with larva
nasal to the optic disc. Vision deteriorates further. in the anterior chamber.
● Stage 4. The two hyper-reflective lesions join to form ● Rare condition.
a broad band of hyper-reflective tapetum. Vision is
noticeably poor at this stage.
● Stage 5. There is generalized retinal degeneration,
Clinical signs
with severely attenuated retinal blood vessels. The
cat is blind. Larval migration of the Cuterebra fly causes vision
loss, usually unilateral, associated with chorioretinitis.
Typically the cat is presented with a cloudy painful eye.
Diagnosis There are usually poor pupillary light reflexes in that
eye, and anisocoria, if the condition is unilateral.
Diagnosis is based on clinical signs, in particular
observation of the typical retinal lesions, and a history The characteristic fundoscopy signs are linear hyper-
of inappropriate diet. reflective “tracks” in the tapetal fundus, and linear
light gray areas of reduced pigmentation in the non-
Electroretinography (ERG) can be performed to
tapetum. Hemorrhage may be evident in the early
identify altered photoreceptor function. Cones ap-
stages. Sometimes the white body of a fly larva is
pear to be affected more than rods, so these cats will
seen associated with one of the tracks.
have reduced b waves in photopic (light) conditions,
and better responses in scotopic (dark adapted) condi- Rarely, the larva is seen in the anterior chamber, with
tions. associated signs of anterior uveitis.
Measurement of plasma taurine levels is the best way
to diagnose the condition. Cats with plasma taurine
Diagnosis
levels below 40 nmol/ml are regarded as deficient.
Diagnosis is based on appearance of the fundoscopic
lesions, or observation of the parasite in the anterior
Treatment chamber and associated uveitis.

Provide taurine supplementation.
● 250–500 mg PO q 12 h.
Treatment
● In the early stages, retinal damage can be reversed,
but ophthalmoscopic signs remain unchanged. There is no specific treatment.
● The effects of prolonged deficiency are only par-
Do not kill the parasite, as this may cause a severe
tially reversible.
immune reaction to the parasite proteins.
● The ERG signs associated with rod degeneration
may reverse, but cone degeneration never totally Topical and systemic corticosteroid therapy is used
recovers. to minimize the inflammation in the affected eye.
Advanced cases will remain irreversibly blind, A free-moving parasite in the anterior chamber or vitre-
despite treatment. ous should be surgically removed.