Page 1249 - Problem-Based Feline Medicine

60 – THE CAT WITH ABNORMALITIES CONFINED TO THE CORNEA 1241

Infection is via contamination of mucous membranes Clinical signs
(ocular, oral or inhalation of virus).
Clinical signs vary from a faint coffee-colored staining
of the axial (central) super-ficial cornea to a dense
Prevention black plaque.

Vaccination with live modified or killed vaccines (see There may be a history of previous infection with
page 10). FHV-1 as a kitten, or later in life, herpetic keratitis.
Elimination of carrier states in catteries. The disease is initially seen unilaterally, but eventually
both eyes may become involved.
Only use killed vaccines on clinically affected animals.
Initially the cat may not show any signs of discomfort,
CORNEAL SEQUESTRUM (FELINE but as the lesion progresses blepharospasm and pho-
KERATITIS NIGRUM)** tophobia develop.
Early, light-staining lesions have an intact epithelium
Classical signs and do not stain with fluorescein. Lesions that have
developed a dense plaque may have a fine ring of
● Area of pigmented cornea varying from
ulceration surrounding the lesion which may stain
a very light coffee-colored stain to an
positive with fluorescein.
intense thick black plaque.
● +/- Blepharospasm and photophobia. The surrounding cornea will not show signs of edema
● Predominantly in brachycephalic breeds or vascularization in mild cases, but as the degree of
such as Persians and Himalayans. degeneration progresses, corneal edema with marked
● Usually unilateral. deep stromal vascularization may be prominent.
Eyes that have a faint stain usually do not have any ocu-
Pathogenesis lar discharge. Eyes that have a dark plaque with sur-
rounding ulceration and intense corneal vascularization
This disease is unique to cats and has an unknown
often have a mucopurulent ocular discharge.
cause.
The disease is seen predominantly in Persians and
Recent research suggests that FHV-1 keratitis may
Himalayans, but any breed can be affected.
play a role in about 80% of cases.
There is no sex or age predilection, but it is more com-
Other causes include corneal ulceration, chronic
mon in adults.
corneal trauma from medial entropion, and disruption
of the tear film on exposed globes.
Diagnosis
It is a corneal stromal disease characterized by degen-
Diagnosis is based on the clinical signs of a mild brown-
eration of collagen and fibro-blasts. The surrounding
staining cornea to a dense black plaque with keratitis.
stroma is usually infiltrated with a mixed population of
white blood cells including neutrophils, lymphocytes, Histopathology of resected cornea will show a typical
plasma cells, and less commonly macrophages and pattern of degenerated stroma surrounded by a ring of
giant cells. The degree of pigmentation varies with the inflammatory cells.
degree of stromal degeneration.
PCR tests on resected cornea may confirm the pres-
Lesions vary in depth from superficial stromal degen- ence of FHV-1 infection but results are usually
eration to full-thickness degeneration as deep as unequivocal.
Descemet’s membrane.
Differential diagnosis
The source of pigmentation has not been established,
but is probably absorbed by the damaged stroma from There are no other ocular presentations that present
the tear film pigments, particularly porphyrins. with a brown discoloration.