Page 1295 - Problem-Based Feline Medicine

62 – THE CAT WITH ABNORMAL PUPIL SIZE, SHAPE OR RESPONSE 1287

most cats dying within 2 years from other manifesta-
ANISOCORIA ASSOCIATED WITH BLUE
tions of the feline leukemia complex.
IRIDES AND DEAFNESS IN WHITE CATS*
Classical signs
FELINE HEMIDILATED PUPIL SYNDROME*
● White cat with behavioral signs suggesting
deafness.
Classical signs
● With a unilateral blue iris, pupils are
● D-shaped pupil in the left eye or reverse uneven sized (anisocoria) with a larger
D-shaped pupil in the right eye. pupil on side of blue iris.

Clinical signs
Pathogenesis
Reduced pigmentation of the iris causes blue iris
Cats have two short ciliary nerves carrying only
coloration in a white cat. These cats also have reduced
parasympathetic fibers from the ciliary ganglion,
pigment in the retinal pigment epithelium and
referred to as the malar (lateral) and nasal (medial)
choroid, and have no tapetum. Where the lack of
nerves. The malar nerve innervates the lateral half of
pigment is unilateral, there will always be an aniso-
the iris sphincter, while the nasal nerve innervates
coria, with the non-pigmented side having a larger
the medial half. The dog in contrast has 5–8 short cil-
pupil. This is thought to be the result of an abnormal-
iary nerves which contain both sympathetic and para-
ity of the pupillary light reflex, caused by the effect of
sympathetic fibers.
lack of pigment on the development of the afferent
Damage to the malar nerve results in constriction of pathways to the lateral geniculate nucleus and pretectal
only the medial half of the pupillary constrictor mus- nucleus.
cle, while damage to the nasal nerve will cause con-
White cat with behavioral signs suggesting deafness.
striction of only the lateral half of the muscle during
miosis.
Diagnosis
Diagnosis is based purely on the clinical signs occur-
Clinical signs ring in a white cat.
Pupil appears as D shaped in the left eye or reverse D
shaped in the right eye. The D shape is accentuated by IRIS ATROPHY*
stimulating the pupillary light reflex with a bright light.
Classical signs

● Loss of normal iris color associated with
Diagnosis increased transparency of the iris in an old
cat.
Based entirely on the observation of a D- or reverse
● Dilated pupil with sluggish pupillary light
D-shaped pupil.
reflex (PLR).
Treatment Pathogenesis

No specific treatment is indicated. Some will reverse Age-related atrophy and thinning of iris structures
over time, provided the nerve has not been completely occur, especially involving the anterior stroma, pupil
transected. margin and associated pupillary constrictor muscle.