Eye Ulcers & Abscesses
Part
III of a series on equine eye care.
Story &
Photos by Tracy Williams
|
In
part two of our eye series, we discussed the basics of caring
for an eye wound. With timely treatment, many eye problems
will dissipate, but, unfortunately, these injuries can often
progress beyond the simplicity of a mere scratch. Eye injuries
can quickly become complicated by infection, which makes treatment
more difficult and healing more delayed.
|
Bacterial
and Fungal Ulcers
An eye injury’s significance is correlated to how deeply
it descends and what corneal tissues it affects. When a wound
touches only the surface layer of the cornea, the epithelium,
it is termed an abrasion. Generally, with the appropriate therapy
as mentioned in part two, these abrasions heal without issue
fairly quickly. However, if the wound extends deeper and affects
the stromal layer of the cornea, it becomes an ulcer. Ulcers,
even with treatment, can rapidly wreak havoc on the eye; they
require aggressive treatment and take much more time to heal.
|
This horse was diagnosed with a stromal
abscess. Luckily, with aggressive treatment this horse's vision
was saved. |
In
any part of the world, the equine eye is constantly exposed
to bacteria and fungi, but in warm, moist climates like the
Southeastern United States, these microorganisms thrive. Normally
the corneal epithelium provides an adequate barrier to infection,
but in the event of eye trauma, fungi and bacteria can filter
in from the eye’s surface and invade the stroma, according
to Dennis Brooks, DVM, PhD at the University of Florida. Unfortunately,
these microorganisms and the body’s response to them can
catapult the wound to a melting ulcer. White blood cells raid
the injury and produce enzymes that further destroy the collagen
that makes up the stroma. The decaying tissue solicits more
white blood cells, which release more enzymes causing more damage
– resulting in a vicious cycle that can destroy the eye.
“Corneal ulceration is the most serious ocular disease
for veterinarians,” says Dr. Brooks. “Regardless
of the initial cause, all ulcers have the potential to progress
to blindness if not treated.”
The signs of a bacterial or fungal ulcer are swelling, discharge,
droopy eyelids, squinting and tearing. To isolate the specific
identity of the bacteria/fungi, you can perform a culture, biopsy
or cytology, according to your veterinarian’s recommendations.
The initial medical therapy is similar to that of an abrasion,
as described in the last issue: an antibiotic/antifungal to
combat the microbes, blood serum to counteract the melting of
the ulcer, atropine to keep the eye dilated, and an anti-inflammatory
to ease pain and swelling. If medical therapy fails, there are
surgical options available.
Corneal
Stromal Abscesses
|
Occasionally,
a bacterial/fungal ulcer can deteriorate into an abscess, defined
as a localized collection of dead tissue. When the eye is damaged
and an ulcer forms, the corneal epithelial cells can grow over
the wound; this is a normal pathway of healing but dangerous
because it can trap bacteria, fungi or foreign bodies in the
stroma, and an abscess can form, according to Dr. Brooks. Unfortunately,
the epithelium then provides a barrier to topical medications,
protecting the bacteria/fungi from being destroyed. Furthermore,
the microorganisms and dead tissue release growth factors and
proteins, encouraging migration of white blood cells into the
abscess.
|
Horses
receiving multiple topical eye medications are often fitted
with a lavage system to ensure all the medicine infuses
the eye.
|
|
The white blood cells not only release enzymes that break down
stromal collagen – like previously discussed – but
they also inhibit blood vessels from growing into the lesion,
which retards healing. As the collagen breaks down, it stimulates
more white blood cells, and the cycle continues until the eye
is destroyed.
Signs
of an abscess are evidence of previous trauma (i.e. ulceration
of the eye), swelling, and a yellow/white stroma indicating
infection.
Prognosis of these injuries depends on their size and position
on the eyeball; the closer they are to the center of the eye,
the more difficult the treatment is because those wounds are
further from blood vessel invasion. “Stromal abscesses
do not completely heal until they become vascularized,”
says Dr. Brooks. They need to be raided by blood vessels;
once the blood vessels grow into the wound, they bring the
anti-collagenases, which fight enzyme activity, preventing
collagen breakdown and preserving the integrity of the eye.
In addition, the blood carries the oral medications to the
wound, which infuse it 24 hours a day – more effective
than topical medications, which only make contact a few times
a day. Unfortunately, blood vessels only grow 1 mm/day, and
the direction of growth can’t be controlled. Therefore,
the closer the wound is to the blood vessels, the closer it
is to being infiltrated and healed. In addition, the blood
vessels have to grow into the wound, not just over it. “If
they grow superficial to the abscess, it won’t do anything
except we won’t be able to see the abscess anymore.
If they grow deeper, it will heal more quickly,” says
Dr. Brooks. If the blood vessels grow into the abscess, initially
it should be red, proving that the blood vessels are doing
their job. Slightly pinker blood vessels indicate that they
have moved deeper into the wound. Ideally from this point,
the blood vessels should get pinker and pinker, eventually
turning white, which indicates that they have eradicated the
infection.
Generally, Dr. Brooks recommends attacking abscesses with
medication first before exploring other, more-pricey options.
Again, horses are generally prescribed an antibiotic, atropine
and anti-inflammatory with an added anti-fungal medication
if needed; horses are often fitted with a lavage system to
ensure all topical medication reaches the eye. In the event
that medication doesn’t work, surgery is an option;
while it is often effective, it is a last resort – only
used when medication fails.
The
Waiting Game
The hardest task in treating eye wounds is the wait. You must
continue applying medications, watch the blood vessels crawl
across the eye, watch for symptoms to recede and wait. It
is simply a game of time. “It’s what we call a
rollercoaster disease. One day you will feel up here, and
the next day you will feel down there,” says Dr. Brooks.
“It’s an up and down disease, and it’ll
drive you crazy.” Patient persistence is key. Even though
healing depends heavily on the eye’s response, the role
of the human in presenting timely, aggressive treatment cannot
be overemphasized.
Resources:
Brooks, Dennis E. “Bacterial Corneal Ulcers.”
The Horse. May 2002.
Brooks, Dennis E. “Fungal Ulcers in the Equine Eye.”
The Horse. June 2002.
Brooks, Dennis E. “Corneal Stromal Abscess.” The
Horse. August 2002.
|
Tracy
Williams is a gradusate of Colorado State University
with degrees in Equine Science and Journalism. She is
a freelance writer and photographer living in New Mexico. |
 |
|
|
|
