Information Sheets
Small Animal Ophthalmology
Corneal Sequestrum
Eosinophilic keratoconjunctivitis
Spontaneous Chronic Corneal Epithelial Deficit (SCCED, Indolent ulcer)
Kerato-conjunctivitis sicca (Dry eye)
Corneal sequestrum (FCS) is a
disease of the cat (although it has been described in the horse). There is a
breed predisposition ( e.g. Persian, Birman, Himalayan, Siamese) and a tendency
for the condition to appear after previous corneal insult (trauma, feline
herpesvirus infection). Corneal sequestration is usually unilatera except in
predisposed breeds. The clinical appearance of the condition is characteristic.
It ranges from small to extensive oval or circular lesions that are usually in
the central or paracentral cornea. The lesion is invariably pigmented but the
intensity of the discoloration ranges from a diffuse, amber stain to a
well-defined back lesion. A discrete zone of oedema or frank ulceration may
surround the sequestrum, and there is usually obvious neovascularisation.
Associated ocular signs include variable degrees of discomfort, discharge,
corneal ulceration and neovascularisation. Sequestra may remain static for
several years or develop rapidly over days or weeks. The lesion may slough
naturally from the corneal surface or extend to Descemet's membrane and lead to
corneal perforation. A comprehensive ocular examination to exclude complicating
factors such as medial entropion, tear film abnormalities and infection would be
indicated. The role of feline Herpesvirus has been discussed: about 55% of
affected cats are positive for FHV-1 DNA when corneal scrapings are assayed
using the sensitive polymerase chain reaction (Nasisse et al., 1996).
Treatment: the time course is reduced considerably if the lesion
is removed surgically, so this is usually the treatment of choice. Keratectomy
combined with a graft, usually a conjunctival pedicle graft or a
corneoconjunctival transposition gives good results. Inevitably, there is some
corneal scarring when the sequestrum involves the stroma, but this improves
dramatically with time. After surgery, the patient is usually given a 7 to
10-day course of topical antibiotic. Recurrence is unsual but it has been
reported. Sectioning the graft has been associated with recurrence of the
sequestrum.
EOSINOPHILIC KERATOCONJUNCTIVITIS
Eosinophilic keratitis (or proliferative
keratoconjunctivitis) is another ocular condition unique to the feline and
equine eye. The cause of the condition is unknown. The course of the feline
disease shares some similarities with the canine chronic superficial keratitis
.Skin lesions of the eosinophilic granuloma complex are absent. In one report,
FHV-1 has been demonstrated by PCR analysis in 76% of affected cats.
Clinical findings: Corneal lesions include edema,
vascularisation, white masses and white plaque formation. They extend from the
limbus. Similar plaques may be found on adjacent bulbar and palpebral
conjunctiva. Chronicity is associated with patchy depigmentation, low-grade
inflammation, small granulomas and eyelid thickening. The condition is usually
unilateral initially, but without effective treatment it frequently progresses
to affect both eyes.
Diagnosis: The diagnosis is based on the
observation of characteristic clinical signs (i.e., plaque). The corneal
cytology demonstrates an infiltration of eosinophils, mast cells, lymphocytes
and neutrophils.
Treatment: The feline eosinophilic /proliferative
keratoconjunctivitis responds to topical corticosteroids and cyclosporine
therapy (application: 2 times daily) . Oral megestrol is also effective but not
recommended because of the side effects. Treatment achieves control but not cure
of the disease.
SPONTANEOUS CHRONIC CORNEAL EPITHELIAL DEFECT
(SCCED, INDOLENT ULCER, BOXER ULCER)
In these situations the ulcer fails to heal because the
epithelium cannot form a proper bond with the underlying stroma. Typically dogs presenting to us with non healing ulcers are middle
aged or older. There is no sex predisposition and it can affect any breed of
dog, although Boxer and Corgi breeds seem to be overepresented. We would
routinely undertake a complete ophthalmic examination in these patients with
particular attention to ensuring that an eye with a SCCED has the ability to
blink correctly, that there are no abnormally positioned eyelid hairs or foreign
bodies which might be rubbing on the cornea and that there is a normal layer of
tears covering the eye.
The symptoms that
may be seen include variable ocular discomfort (from almost no discomfort to
moderately painful eyes), a bluish discolouration of the corneal surface and the
presence (but not always) of blood vessels growing into the cornea (often
appearing as a red fringe in the outer portion of the cornea). A loose lip of
epithelium often surrounds the ulcer, although specialist equipment may be
needed to see this. Often a cornea will show what appear to be multiple ulcers
although these invariably join into one large ulcer when poorly attached
epithelium is removed.
Here are several routine treatment options for SCCEDs
in Boxers including chemical cautery of the ulcerated site, repeated corneal
debridement and surgery. Our preference is to perform a thorough removal of any
epithelium on the eyes surface that is poorly attached under a short anaesthetic
(although in some patients the surgery can be done awake with local anaesthetic)
this invariably enlarges the area of ulceration but it means that we strip the
epithelium back to a point of healthy attachment which is key to successful
treatment in our minds. The stroma which has been laid bare of epithelium is
then treated by creating hundreds of microscopic pricks to the corneal surface
with a tiny needle (a punctate keratotomy) or creating microscopic channels in
the stroma (a grid keratotomy). These procedures promote much stronger bonds
between the epithelium and skin and leads to the resolution of the ulcer in the
overwhelming majority of our cases within 10 to 14 days. In cases that fail to
respond to this line of treatment, a superficial keratectomy may be performed
which involves the removal of thin layer of stroma. Corneas which have undergone
any surgery typically receive a range of medications including antibiotics,
promoters of healing (such as serum drops) and pain
relief. We routinely place bandage contact lenses (rather than performing third
eyelid flaps which are not without potential problems) to improve comfort after
surgery and to protect the cornea during its early healing period. Once a
treated area of cornea has healed it is rare for further SCEEDs to develop at
these sites so there is invariably a positive outcome in those cases which
receive appropriate treatment.
KERATOCONJUNCTIVITIS SICCA (kcs)
Dry eye is a consequence of tear deficiency or increased evaporative
loss (often related to meibomian gland disease or eyelid problems), or a
combination of the two. Breeds that are over represented with this disorder
include English bulldogs, American cocker spaniels, West Highland white
terriers, Lhasa Apsos, Shi Tzus, Pugs, Pekingese, Boston terriers, Cavalier King
Charles spaniels, Yorkshire terriers, and miniature poodles. Clinical signs may
include pain (seen as blepharospasm), decreased aqueous tear production as
measured using a Schirmer tear test strip (normal tear production 15 mm/minute
or greater), mucoid to mucopurulent ocular discharge (due to the lack of
"flushing" of the mucous portion of the precorneal tear film by the aqueous
portion), recurrent "eye infections" (due to overgrowth of normal flora and
pathogens), corneal neovascularization and pigmentation, and/or potentially
proteolytic enzyme ulcers ("melting ulcers") from endogenous or bacterial
proteolytic enzymes.
Clinical signs include from mild to severe mucopurulent discharge,
conjunctival hyperaemia, lacklustre cornea (poor corneal reflex), corneal
pigmentation and vascularisation. Discomfort is a constant feature. Some cases
can present acutely. Any dog with conjunctival or corneal disease should receive
a STT test.
Treatment of KCS involves tear suplemments, antibiotics, mycolitics,
anti-inflammatories and lacrostimulants. We currently use topical sodium
hyaluronate drops (as lacrostimulants), which are formulated in a hypotonic
solution. It was recently demonstrated in a human study that a hyaluronate
receptor is expressed in corneal and conjunctival cells, suggesting a role for
hyaluronate in cell adhesion and motility. It was also proposed that hyaluronate
may have a role in controlling the localised inflammation often present in
patients with KCS. Regarding lacrostimulants if it is early in the disease we
tend to use Optimmune (cyclosporin 0.2%). If STT fails to increase on this
concentration, we increase to cyclosporin 1% and 2%. Tacrolimus is the "new"
drug that is used in the management of KCS. It is a macrolid antibiotic that is
a potent modulator of the immune response to antigens by inhibiting T-lymphocyte
activation. In cases where topical medication, parotid duct transposition should
be considered.
