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CO R N E A L D I S E A S E
IN SUMMARY:
●
eye conditions can be very
serious, if concerned, always
seek veterinary advice;
●
seek veterinary attention if the eye
does not quickly improve after
cleaning or does not respond to
treatment recommended by your vet;
●
corneal ulcers should always be
treated aggressively no matter how
small they appear to be;
●
always inform your vet if you are
unable to get the drops into the eye,
alternative methods of medication can
then be found;
●
your horse, pony or donkey may be
left with some corneal scarring; this
is cosmetic and shouldn't necessarily
be seen as a poor outcome.
AUTUMN 2012 ISSUE
Figure 3
- keratitis in a donkey. Note the
opaque/cloudy cornea and tiny blood vessels
running across the surface
Figure 4
- a corneal ulcer after fluorescein
stain has been applied
Figure 5
- the corneal ulcer above after the
edges were debrided
Diseases of the cornea
●
corneal ulceration
- damage to the
surface or deeper layers of the cornea
●
keratoconjunctivitis sicca (dry-eye)
- failure of tear production leading to
a roughening of the corneal surface
●
tumours
- e.g. squamous cell
carcinoma
●
keratitis
- inflammation of the cornea
(Figure 3).
Corneal ulceration is the most frequently
occuring equine corneal condition.
Most corneal ulcers are due to bacterial
infection, even if it was not the initial
cause. Fungal and viral infections can
also occur but are less common.
Corneal ulcers often have a flap of dead
tissue overlying the edges (Figures 4
and 5). Removing this tissue (debriding)
under sedation and local anaesthetic will
initiate or assist healing by allowing the
cells to migrate across the ulcer - the
direction of healing occurs from the
outside edge inwards.
The treatment of
corneal ulcers:
●
antibiotic eye ointment or drops;
●
pain relief - injectable and oral pain killer
anti-inflammatories (e.g. phenylbutazone);
●
autologous serum drops - the patient's own
serum is collected from a blood sample
and stored in the refrigerator to be applied
to the affected eye;
●
antibiotics given by injection or in feed
may be used in some cases.
Applying serum to the eye (autologous
meaning the patient's own) might appear an
odd thing to do. Serum and other agents such
as EDTA, are given to reduce the damaging
effect that the enzymes contained in the tear
film can have on the ulcer.
●
Corneal ulceration is the commonest
equine eye condition and progression
to more complicated corneal disease
is more common than in other
domestic species.
●
Diagnosing and treating a diseased/
injured eye can be very challenging
depending on the size and
temperament of the patient.
●
The equine patient has a very powerful
blink reflex meaning that opening the
upper eyelid to examine the eye and
apply topical medication can be difficult.
●
The equine cornea is uniquely slow to
heal in comparison with other species.
Equine corneal disease:
key complications
Contact lenses
Some cases may benefit from having a soft
contact lens applied. They are often called
bandage lenses because they protect the
cornea, particularly from the rubbing of the
eyelids. The lenses are porous allowing
medication to pass through. The correct
size must be fitted otherwise they will just
aggravate the eye or fall out. They are
relatively expensive too so need to stay in
for several days to justify the expense.
Figure 6
- a soft bandage contact lens, the
green emblem is just visible
EQUINE MATTERS
12
The sub-palpebral lavage
system
If your horse is compliant and you are able
to get the medication in, a lavage system
will not be necessary. However, getting
medication into the eye can sometimes be
very difficult so using a lavage system
(Figures 7 and 8) can be a great help.
It can be placed in the upper eyelid or
the lower lid.
Figure 7
- a lavage system fitted and stitched
in place
Figure 8
- showing the lavage system
threaded through the plaited mane. The
green arrow shows the portal where
medication is injected