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 The
cornea is a clear organ that makes up the front portion of the eyeball.
A thin layer of cells called the epithelium covers the cornea.
The epithelium is responsible for protecting the cornea from
damage. When the epithelium is disrupted, the
underlying cornea may become damaged, infected or both.
When the epithelium is damaged in the underlying cornea is
exposed we refer to the situation as a corneal ulcer.
The
cornea is very sensitive organ and when it is damaged he can be quite
painful. Whenever there is a corneal ulcer, the
muscles of the iris, which formed the pupil, contract in spasm.
This spasming contributes to the pain associated with corneal
ulcers. If you look at the eye of the pet with
ulcer, you'll notice that the pupil on the affected side is smaller in
general then the non-affected side. In addition, the
eyelid tends to spasm as well in the pet appears to be squinting.
Under
normal circumstances, damaged corneal epithelium will slide across the
cornea to seal itself in a matter of days. However,
in order for this to occur the cornea must be free of foreign material
or infectious agents and the corneal tissue needs to be healthy.
How
do we diagnose a corneal ulcer?
The
normal cornea when it is covered with epithelium will not be able to
absorb a special diet called flourescein. Therefore
in order to detect a scratch in the corneal epithelium, the veterinarian
will apply flourescein dye to the eye. If there is
an ulcer, the eye will turn green and will actually fluorescent or glow
under an ultraviolet light.
How
to we treat corneal ulcers:
First
and foremost in the treatment of any corneal ulcer, is to be sure that
there is no foreign material in the eye socket causing the ulcer.
This could include the presence of plant materials such as Fox
tales, sand or grit, or inverted eyelashes. The
doctor and will examine the eye usually with the aid of a topical
anesthetic and remove any foreign material is visible.
If eyelashes are found to be inverted, a surgical procedure may
be necessary to correct the anomaly.
The
amount of damage to the cornea is graded from superficial, to moderate,
to deep. Superficial ulcers involve the very surface
portion of the cornea and frequently will heal within a few days after
therapy is instituted.
Generally the deeper the ulcer the more involved the treatment becomes.
Most superficial ulcers may be cured by using antibiotic ointment
or drops along with the drug to help dilate the pupil called atropine.
In addition, in Elizabethan collar is placed around the head to
protect the eye from further damage.
Deeper
ulcers may require additional drugs such as Adequan drops, or Muro 128
ointment. In addition, we frequently check the eye
for bacterial infection by sending a culture and sensitivity test off to
the laboratory to make sure we have selected the appropriate antibiotic
ointment.
If the
corneal epithelium is unhealthy, and is not sticking properly to the
cornea itself than we will have to do a procedure known as corneal
debridement. In this procedure, the pet is placed
under anesthesia and the abnormal corneal epithelium is removed.
With the bad epithelium gone, new epithelium should be able to
migrate across the cornea and seal the ulcer. In
some cases, the cornea itself is diseased or abnormal and will not
accept the epithelium. In these cases more
aggressive debridement is necessary. Sometimes we
will rough up the cornea with a scalpel or laser to make it easier for
the epithelium to stick to it. In some cases, we
actually have to remove a small amount of the cornea to expose fresh
cornea for the epithelium to stick to. Some breeds
such as the box or, Boston terrier or Shih-tzu have a propensity to
develop corneal ulcers. In fact, when these breeds
develop ulcers they frequently develop ulcers in the other eye within a
year of the initial injury.
If I
treatment is successful, and the corneal epithelium seals itself, the
body will try to heal the wound by bringing new blood vessels in towards
the injury. These blood vessels obscure the clarity
of the cornea and can impair the sight. Once the
ulcer is closed and no longer stains positive with flourescein, then we
will add a new drug containing a cortisone compound, which will help
eliminate the blood vessels and prevent scarring of the cornea.
In the end, are desired result is to have a clear scar free
cornea.
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