Page 1340 - Problem-Based Feline Medicine

1332 PART 15 CAT WITH EYE PROBLEMS

continued

TRAUMA
● Trauma to the third eyelid* (p 1330)
Asymmetric notch-like defects in the third eyelid margin due to claw injury from fighting with
other cat(s).
● Sympathetic neuropathy of the third eyelid (Horner’s syndrome)** (p 1335)
Prominent third eyelid, usually unilateral, in association with any combination of enophthalmos,
upper lid ptosis or miosis, in association with or without other localizing signs such as ipsilateral
forelimb lameness, cervical lesions (e.g. abscess, cellulitis) or middle ear disease.

page 1212) can also involve the surface of the third eye-
INTRODUCTION
lid. Such conjunctival diseases are either:
● Inflammatory disease due to:
MECHANISM? – Infectious agents such as FHV1, Chlamydophila
felis, Mycoplasma.
The most common cause of change in third eyelid – Non-infectious, allergic or other immune-medi-
appearance is an abnormality in innervation, especially ated etiologies, e.g. eosinophilic keratoconjunc-
involving the autonomic sympathetic nerves. tivitis or follicular conjunctivitis.
● Neoplastic disease, especially squamous cell car-
The abnormal third eyelid is most often noticed
cinoma.
because it is prominent.
Prominence or protrusion of the third eyelid is a pas-
WHERE?
sive phenomenon in most animal species. Protrusion is
usually facilitated by active contraction of muscle in Disease anywhere along the sympathetic neural path-
adjacent orbital structures, and occurs because either: ways (i.e. thalamus, cervical spinal cord long tracts,
● The globe is retracted caudally into the orbit by the T1–T3 spinal nerves, ascending pre-ganglionic
action of the rectus and retractor bulbi muscles (the fibers, cranial cervical ganglion, sympathetic post-
normal position of the globe tends to push the third ganglionic fibers in middle ear or orbit), and the
eyelid into its retracted position at the medial aspect smooth muscle fibers innervated by them, may cause
of the globe) or protrusion of the third eyelid.
● Sympathetically innervated smooth muscle at the
Conjunctival surface diseases cause abnormal appear-
base of the third eyelid (arising from deep in the
ance of the third eyelid.
orbit around facial coverings of the medial and ven-
tral rectus muscles) is not contracting, causing Cartilage of the third eyelid may fold causing an
a failure of retraction of the third eyelid. everted appearance.
In the cat, the third eyelid may become actively pro-
truded, independent of globe movement, by the action WHAT?
of skeletal muscle fibers, which are extensions of
The most common cause of altered third eyelid appear-
the levator palpebrae superioris and the lateral rectus
ance is autonomic nervous system disease especially
muscles, innervated by the oculomotor (CN III) and
primary third eyelid dysautonomia (“haws”).
abducens (CN VI), respectively.
Horner’s syndrome is associated with other clinical
Because the third eyelid is covered by conjunctiva signs such as enophthalmos, miosis and upper lid pto-
on both its posterior and anterior surface, any disease sis. Primary third eyelid dysautonomia is associated
which affects the conjunctiva (see The Cat With Ocular with prominence of the third eyelid with lack of
Discharge or Changed Conjunctival Appearance, other signs of sympathetic denervation.