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 layer is the epithelium. Actually, this layer is
comprised of many, very thin layers of cells. 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
An erosion thorough a few layers of the epithelium is called a corneal erosion
or a corneal abrasion
. A corneal
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. Causes
There are several causes for corneal ulcers in pets. The most common is trauma. An ulcer may result from blunt
trauma, such as a pet rubbing its eye on 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. A
third cause is seen in breeds of pets with protruding eyes such as Shih Tzu, Lahsa Apso, Pugs, Persian cats and other
similar breeds. These pets may not be able to close their eyelids completely when they blink so the center of the
cornea gets dry and is not protected by tears.
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. Examples of other diseases include
Epithelial Dystrophy (a softening of the cornea which is inherited in breeds such as the Boxer), Keratoconjunctivitis
Sicca (drying of the cornea due to abnormal tear formation), and diseases of the endocrine system (diabetes mellitus,
hyperadrenocorticism, and hypothyroidism). Clinical Signs
A corneal ulcer is very painful. In response to pain, most pets rub the affected eye with a foot or on the carpet. 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. There may be a blue or cloudy hazy to a portion of the cornea as well. Diagnosis
Superficial corneal abrasions are usually not visible. They can be visualized with the use of fluorescein stain. A
drop of this 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. Treatment
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 4 to 6 times per day.
On the other hand, the effects of atropine last many hours so this drug is only used twice daily.
If a corneal ulcer or descemetocele is present, measures must be taken to protect the eye and to promote healing.
Since pets 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, then are reversed so the pet 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. Mistake in Treatment
It is possible to mistake a corneal abrasion from a corneal ulcer when the latter is very superficial. Therefore, after
2-3 days of treatment, your pet should be reexamined to be sure that healing is progressing properly. If that does not
happen, a decision may be made to perform surgery.
Side-effects of Eye Medications
Rarely, a pet will be allergic to an antibiotic that is instilled in the eye. If your pet seems more painful after the
medication is used, discontinue it and contact the veterinarian.
A pet 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 pet 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. Drooling After Treatment
The tear ducts carry tears from the eyes to the back of the nose. The eye medications may go through the tear ducts
and eventually get to the throat where they are tasted. Atropine has a very bitter taste that may cause drooling and
pawing at the mouth. You are seeing your pet’s response to a bad taste, not a drug reaction. Use of Topical Anesthetics to Control Pain
A topical anesthetic is often used to numb the cornea so the diagnostic tests may be performed. However, these
drugs are toxic to the corneal epithelium; they prevent proper healing. They are safe for one time use, but they
should not be used as part of treatment. Use of NSAID’s to Control Pain
NSAID’s, or NonSteroidal Anti-Inflammatories, are often used to help control the pain of a corneal abrasion or
ulcer. Examples of NSAID’s are Metacam, Rimadyl, and Deramaxx though there are others as well. One of these
drugs may be prescribed to help control the pain from the ulcer or abrasion.
A drug called Tramadol, or Ultram, may also be prescribed for control of eye pain.
Both of these medications are given orally at home for pain. Conclusion of Treatment
The best way to tell that the cornea has healed is to repeat the fluorescein stain test. This should be done after about
5-7 days of treatment.
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 good 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 remove them.
This is done with corticosteroid (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 corticosteroids not be 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 the eye becomes painful again, discontinue the steroids and have the eye rechecked. Never use a left over eye ointment in your pet’s eye if you think it has a corneal abrasion or ulcer. It you are accidently using the wrong medicine you could make the ulcer much worse. It is much safer to see your veterinarian as soon as possible to have the eye stained and examined for an ulcer.
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