Facts About Non-Healing
Corneal Ulcers
What is a corneal ulcer?
The cornea is the outer clear "window" of the eye, and is composed
of several layers. The outer layer is the "skin" of the cornea, and is called
the corneal epithelium. The layer is very thin (about 8-12 cells thick), and covers
the deeper corneal tissue (called corneal stroma).
A corneal ulcer is a defect in the epithelium, causing the underlying
stroma and corneal nerves to be exposed, which causes
pain and inflammation. An ulcer can be superficial (involving loss of only the
epithelium), or deep (extending into the stroma).
Symptoms of a corneal ulcer include: increased redness or cloudiness of the eye,
squinting, rubbing at the eye, and/or increased tearing or discharge from the
eye.
Corneal ulceration is a common in dogs and cats. Trauma, infection,
foreign bodies embedded in the cornea, and abnormally placed eyelashes are just
some of the many conditions that can cause corneal ulceration.
How do corneal ulcers heal?
In a normal cornea, an ulcer heals rapidly (usually in 1-2 weeks,
depending on the size of the ulcer). Healing is accomplished when epithelial cells
divide to form new cells, which then slide over the defect in the cornea until
the entire ulcer is healed. The attachment of epithelium to
stroma is normally very firm, and depends on: 1) anchoring
filaments that pass form one layer to the other, thereby "riveting" the two layers
together, and 2) a glue-like substance (called basement membrane)
that "glues" the epithelium to the
stroma.
What is a non-healing (persistent) ulcer?
In some middle-aged or older animals, a corneal ulcer may fail
to heal, resulting in an ulcer that persists for weeks or months. These ulcers
are called persistent (or non-healing) ulcers. Persistent ulcers occur in humans,
dogs, cats, horses, and other species. The reason some ulcers do not heal properly
is not entirely understood, but most experts agree that persistent ulcers arise
because of age-related problems in the healing mechanism described above.
In persistent ulcers, the epithelial cells divide normally to
make new cells, but the new cells have a hard time "ticking" to the
stroma. This is because the new epithelial cells:
1) do not form anchoring filaments, and 2) they secrete an abnormal ("non-sticky")
basement membrane. Since the newly formed epithelial cells do not create a firm
attachment to the stroma, they are easily peeled off
the cornea by blinking, or by rubbing the eye. Therefore, these ulcers often will
become smaller, then larger, then smaller again, but they never completely heal.
What are the treatments for persistent corneal
ulceration?
Treatment for persistent corneal ulceration is medical, surgical,
or a combination of both. Medical treatment involves treating the eye with antibiotic
medication, and simply letting the healing process continue on its own until completed.
Healing occurs when blood vessels grow into the ulcerated area of the cornea,
thereby eventually "scarring" the epithelial and stroma
layers together. Topical ophthalmic antibiotic medication is applied to the eye
during the healing process. (Antibiotics do NOT make the cornea heal faster -
they are used only to prevent secondary bacterial infection of the cornea while
it is ulcerated.) Healing can take many weeks, months, or even longer than a year!
Although most persistent ulcers will eventually heal on their
own, the eye is uncomfortable and inflamed during this prolonged healing
process. In addition, significant scarring of the cornea can result, and the ulcer
may become infected. Therefore, surgery is usually recommended to speed healing
of the cornea.
What are the surgical treatments for persistent
ulceration?
Surgery greatly speeds healing and reduces scarring to a minimum.
The most commonly used surgery is a simple, quick, painless, technique called
a grid keratotomy (also called a multiple punctuate keratotomy, or linear keratotomy).
This surgery is the recommended treatment for persistent corneal ulceration, and
can be performed immediately after ophthalmic examination is concluded. Anesthetic
drugs are applied to the eye (sedation or general anesthesia is not required unless
the patient is uncooperative). Corneal epithelium is removed from the ulceration
area with a sterile cotton-tipped swab, after which a special needle is used to
make multiple, superficial, grid-like cuts in the ulcer. After performing a grid
keratotomy, most superficial ulcers (about 95%) will be healed within one week.
Antibiotics are continued during the healing process.
In some patients, more extensive surgery is required. This surgery
is called superficial keratectomy. The patient is completely anesthetized, and
the entire outermost layer of the cornea (composed of the epithelium plus the
superficial layers of the stroma) is then surgically
removed. Antibiotics are continued during the healing process. This surgery is
highly effective in healing persistent corneal ulceration, but is usually not
required unless grid keratotomy is ineffective.
A dissolvable contact may be applied after surgery to help protect
the cornea during healing.
Is surgery curative?
Usually, a persistent ulcer will not develop again in the area
of the cornea that has been treated saurgically. However,
since persistent ulceration is an age-associated problem, another ulcer may develop
in the same eye (in a different location from the area that was treated surgically),
or in the other eye. If symptoms of persistent corneal ulceration return in either
eye, schedule a reexamination as soon as possible.
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