Page 1246 - Problem-Based Feline Medicine

1238 PART 15 CAT WITH EYE PROBLEMS

has poor tropism for corneal tissue. Corneal disease is The ocular changes are usually bilateral, but may be
usually the consequence of conjunctival infection in unilateral in older cats.
young cats.
The cornea may be affected in acute infections by for-
FHV-1 affects the cornea through two different mecha- mation of symblepharon. Necrosis of the epithelium,
nisms. probably with stem cell damage, allows the conjunctiva
to permanently adhere to the corneal stroma. The
Firstly, the virus has a direct cytopathic effect on
cornea then heals with a dull gray appearance, covered
corneal epithelium and produces the typical linear or
by a thin membrane of conjunctiva.
branching (dendritic) lesions. The lesions rarely reach
the depth of the epithelial basement membrane, and can In older cats with a carrier status, mild signs of her-
therefore be difficult to detect. Staining the epithelium pesvirus infection may be seen after some form of
with rose bengal may reveal these pink branching stress. In these cases, the inflammation is less
lesions. intense and only a serous discharge is present. These
cats may have a history of respiratory infection as a
Secondly, an immune response to viral antigen
kitten.
causes a prolonged absence of epithelium. This is seen
clinically as a “geographic ulcer”, that is, a large The classical corneal lesions in early infections
ulcer with an irregular shape that appears to look like appear as dendritic (branching) epithelial lesions
a continent or land mass. There may be some fine that can be very subtle in appearance and may require
superficial blood vessels within the anterior stroma in magnification to visualize. They usually occur after
the area that is affected. the primary conjunctival inflammation has decreased
in intensity. The epithelium may be swollen in
The virus is able to replicate and become latent in nerve
affected areas, and these branching lesions may stain
tissue, most likely in trigeminal nerve sensory ganglia.
pink with rose bengal stain. There may be a mild con-
Virus reactivation occurs after stress and after the
junctivitis with a serous ocular discharge
administration of corticosteroids. Vaccination with live
virus vaccines may exacerbate the condition in affected In chronic cases, a stromal keratitis develops.
cases. The condition is frequently unilateral. The epithe-
lium is eroded and there may be mild edema with
Clinical signs some superficial vascularization. The cornea devel-
ops an irregular surface with scarring that is
The earliest sign of classical herpesvirus infection is obvious on clinical examination and this is known
paroxysms of sneezing or salivation. This is usually as a geographic ulcer. This is the calssical form of
seen in kittens and cats that have not been immu- FHV-1 keratitis seen in older cats. It is frequently
nized. only unilateral, and may appear years after initial
Systemic signs of upper respiratory disease are com- infection in cats with no previous history of eye dis-
mon and include anorexia, pyrexia and depression. ease.
Acute conjunctivitis manifested by hyperemia and Chronic stromal FHV-1 keratitis has a history of quies-
chemosis is seen at the same time as the respiratory cent periods followed by signs of ocular pain with ble-
signs. Prolapse of the third eyelid may occur as part of pharitis, photophobia and corneal erosions. There is
the inflammatory process in the eye. rarely conjunctivitis or ocular discharge.
Serous ocular discharge is seen in the acute phase and A black staining color may develop in the center of the
this progresses to a mucopurulent discharge. cornea known as a corneal sequestrum (keratitis
nigrum). This is caused by a stromal coagulative necro-
In young cats, ulceration may occur in the buccal sis, and it has been suggested that FHV-1 infection may
mucosa and on the tongue. be the cause of 80% of these lesions.