CORNEAL ULCERS
The cornea is the clear, shiny membrane that makes up the surface of the eyeball. It is
much like a clear window. To understand a corneal ulcer, you must first understand how
the cornea is constructed.
The cornea is comprised of three layers. The most superficial or outermost layer is the
epithelium. This layer is comprised of many, very thin layers of cells, similar to an onion’s
skin. Below the epithelium is the stroma and the deepest layer is Descemet's membrane.
Because all of these layers are clear, it is not possible to see them without special stains
and a microscope.
An erosion through a few layers of the epithelium is called a corneal erosion or corneal
abrasion. A corneal ulcer is an erosion through the entire epithelium and into the stroma.
If the erosion goes through the epithelium and stroma to the level of Descemet's
membrane, a descemetocele exists. If Descemet's membrane ruptures, the liquid inside
the eyeball leaks out and the eye collapses.
What causes corneal ulcers?
There are several causes for corneal ulcers in cats. The most common is trauma. An ulcer may result
from blunt trauma, such as a cat rubbing its eye on a carpet, or due to a laceration, such as a cat
scratch. The second most common cause is chemical burn of the cornea. This may happen when
irritating shampoo or dip gets in the eye.
Less common causes of corneal ulcers include bacterial infections, viral infections, and other diseases.
These may originate in the eye or develop secondary to disease elsewhere in the body.
What will my cat do if an ulcer is present?
A corneal ulcer is very painful. In response to pain, most cats rub the affected eye with a foot or on the
carpet or furniture. To protect the eye, they keep the lids tightly closed. Occasionally, there will be a
discharge that collects in the corner of the eye or runs down the face.
How is a corneal ulcer diagnosed?
Superficial corneal abrasions are usually not visible. They can be highlighted and seen with the use of
fluorescein stain. A drop of this orange-colored stain is placed on the cornea. The dye will adhere to an
area of ulceration and is easily visualized with a special black light called a Wood's light. This is the
most basic test performed and may be the only test needed if the ulcer is acute and very superficial. If
the ulcerated area is chronic or very deep, samples are taken for culture and cell study prior to applying
the stain or any other medication.
Can an ulcer be treated?
Yes. However, the form of treatment depends on whether there is a corneal abrasion, corneal ulcer, or
descemetocele present.
Corneal abrasions generally heal within 3-5 days. Medication is used to prevent bacterial infections
(antibiotic ophthalmic drops or ointment) and to relieve pain (atropine ophthalmic drops or ointment).
Antibiotic drops are only effective for a few minutes so they must be applied frequently; ointments last a
bit longer but still require application every few hours. It is suggested that an antibiotic preparation be
instilled in the eye four to six times per day. On the other hand, the effects of atropine last many hours so
this drug is only used once or twice daily.
If a corneal ulcer or descemetocele is present, measures must be taken to protect the eye and to
promote healing. Since cats do not wear eye patches well, surgical techniques are often used to close
the eyelids and cover the ulcer or descemetocele. These measures protect the eye for several days and
then are reversed so the cat can use the eye again.
Ulcers that do not heal well often have a buildup of dead cells at the ulcer edge. These dead cells
prevent normal cells from the corneal surface from sliding over the ulcer edge and filling in the defect. If
this appears to be part of the healing problem, the dead cells are removed from the edges of the ulcer
before the eyelids are surgically closed. In some cases, removing the dead cells may be all that is
needed to start the healing process, so surgical closing of the eyelids may not be necessary.
Is there a difference between a corneal ulcer and a corneal abrasion?
It is easy to confuse an ulcer and an abrasion on the first examination. There is a judgment call involved
in differentiating the two. After 2-3 days of treatment, your cat should be reexamined to be sure that
healing is progressing properly. If that does not happen, a decision may be made to perform surgery.
Do any of the medications have side-effects?
A cat will rarely be allergic to an antibiotic that is instilled in the eye. If your cat seems to be in more pain
after the medication is used, discontinue it and contact your veterinarian.
A cat with a corneal ulcer has quite a bit of pain in the eye, so it keeps it tightly shut. Atropine is used to
relieve that pain. However, atropine also dilates the pupil widely. This means that the cat is very
sensitive to light in that eye. Because of the light sensitivity, the eye will be held closed in bright light.
Atropine's effects may last for several days after the drug is discontinued. Do not be alarmed if the pupil
stays dilated for several days. Should you accidentally get atropine in your eye, the same prolonged
pupillary dilation will occur.
Atropine has a very objectionable taste. If it gets in the cat’s mouth, drooling will occur. This is not a drug
reaction but a reaction to the terrible taste. It will subside in a few minutes. However, once this happens,
the cat may be more difficult to medicate because it may anticipate the same thing happening again.
What can I use to control the pain?
A topical anesthetic is often used to numb the cornea so diagnostic tests may be performed. However,
these drugs are toxic to the corneal epithelium and prevent proper healing. They are safe for one time
use, but they should not be used as part of the treatment.
How do I know when the treatment is completed?
The best way to tell that the cornea has healed is to repeat the fluorescein stain test. This should be
done after approximately 5-7 days of treatment.
What does it mean if there are red streaks near the ulcer?
The normal cornea has no blood vessels going through it. However, when a corneal ulcer or
descemetocele occurs, the body senses a need to increase its healing capabilities. New blood vessels
are created by a process called neovascularization. The new vessels begin at the sclera (the white part
of the eye) and course their way to the ulcer.
Neovascularization is a positive response because it hastens healing. However, after the ulcer is
healed, these vessels remain in the cornea. They are not painful, but they do obstruct vision. Therefore,
it is desirable to attempt to remove them. This is done with steroid (cortisone) ophthalmic drops or
ointment. Cortisone is used for a few days to several weeks, depending on how many vessels exist.
It is important that steroids are not used in the eye too soon because they will stop healing of a corneal
ulcer and may worsen it. Therefore, the fluorescein dye test should be performed before beginning this
type of medication. If steroids are used and pain occurs in the eye again, discontinue the steroids and
have the eye rechecked.
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Animal Hospital of Fate 1001 North W.E.Crawford (Highway 66 in Fate) Rockwall, Texas 75087 972-722-0066 |
| Rockwall, Texas 75087 972-722-0066 |