Page 1247 - Problem-Based Feline Medicine

60 – THE CAT WITH ABNORMALITIES CONFINED TO THE CORNEA 1239

Diagnosis ● The inflammation is more intense than herpesvirus
keratitis with greater destruction of stromal tissue
Diagnosis is based on a history of repeat ocular prob-
and more intense edema. Keratomalacia (melting
lems with subtle corneal changes. It is difficult to
cornea) can develop in cases with pseudomonas
establish a definitive diagnosis.
infections.
Cytology: intranuclear inclusions in epithelial cells ● Bacterial keratitis causes a mucopurulent discharge.
can be demonstrated with immunoperoxidase stains ● Cytology from clean scrapings taken from the edge
in some acute primary infections. This is not very of the ulcer may demonstrate bacteria. Culture and
reliable. sensitivity can be done from scrapings taken from
the edge of the ulcerated cornea.
Immunofluorescence: direct or indirect fluorescent
● Ulcers heal without recurrence.
antibody techniques on corneal/conjunctival smears or
tissue sections. This has poor sensitivity. Eosinophilic keratoconjunctivitis.
● This is a proliferative lesion that is usually accom-
Virus isolation by demonstration of cytopathic effects
panied by inflammation and a mucopurulent dis-
in cell culture. This is the gold standard for detection of
charge.
herpesvirus, but is not often used because of logistical
● The presence of eosinophils on cytology is regarded
difficulties in getting rapid results.
as diagnostic.
Serology: antibody titers tend to be of low magnitude
Neoplasia.
after primary infection, sometimes reaching only 1:64
● Squamous cell carcinoma of the cornea is reported,
at 60 days after infection. High titers are rarely seen
but it is a very rare condition in cats. The lesion is
after recrudescent infection.
proliferative but there is little ocular discharge.
Polymerase chain reaction (PCR) testing: DNA ● Cytology or fine-needle biopsy will confirm this
amplification of an amino acid sequence of the thymi- condition.
dine kinase gene is perhaps the most sensitive test
available. Theoretically the test could pick up one Treatment
strand of viral DNA. High sensitivity in nested PCR
tests may reduce specificity by the detection of non- Not all treatments useful for ocular herpesvirus infec-
viral DNA contaminants. Although this test was ini- tion are commercially available throughout the world.
tially heralded as an excellent diagnostic tool, in
Topical and probably systemic corticosteroids are
practice the results have been very disappointing. It
contraindicated in all cases of ocular herpesvirus
would appear that sample collection and individual lab-
infections. The effect of topical NSAIDs has pro-
oratories have a great influence on specificity.
duced equivocal results experimentally. However,
● Conjunctival swabs and/or biopsies are used for
some cases of herpesvirus keratitis may only respond
PCR or virus isolation. Not all laboratories are
if corticosteroids are used in conjunction with antivi-
equipped to do this work. Check with your labora-
ral agents.
tory, as you may have to send samples interstate or
overseas for results. Topical ocular antiviral agents include:
● Idoxuridine inhibits DNA synthesis by competing
with thymidine for incorporation into viral DNA. It
Differential diagnosis
is no longer in production, but has been the most
Ulcerative keratitis. commonly used topical agent for treating FHV-1
● Not common as a primary ocular disease, but is infection. Topical drops are frequently made to
seen secondary to viral infection. order by a compounding pharmacist and produce
● It usually follows ocular trauma. excellent results. Idoxuridine 0.1% drops are