Issue Description An inflammatory condition of the cornea
involving loss of its outer layer. It is very common in dogs and is
sometimes seen in cats. In veterinary medicine, the term corneal ulcer
is a generic name for any condition involving the loss of the outer
layer of the cornea, and as such is used to describe conditions with
both inflammatory and traumatic causes. Other Names Ulcerative Keratitis
Causes Corneal ulcers are one of the most common eye
diseases in dogs. They are caused by trauma, detergent burns, and
infections. Other eye conditions can cause corneal ulcers, such as
entropion, distichiae, corneal dystrophy, and keratoconjunctivitis
sicca (dry eye). There have been at least two cases where corneal
ulceration was caused by canine herpesvirus.
ulcers involve a loss of part of the epithelium. Deep ulcers extend
into or through the stroma and can result in severe scarring and
corneal perforation. Descemetoceles occur when the ulcer extends
through the stroma. This type of ulcer is especially dangerous and can
result in perforation.
The location of the ulcer depends
somewhat on the cause. Central ulcers are typically caused by trauma,
dry eye, or exposure from facial nerve paralysis or exophthalmos.
Ulcers in the inferior nasal cornea may be caused by foreign material
trapped under the third eyelid. Entropion or distichiae may cause
ulceration of the peripheral cornea. Immune-mediated eye disease can
cause ulcers at the border of the cornea and sclera.
Symptoms Corneal ulcers are painful due to nerve
exposure, and can cause tearing, squinting, and pawing at the eye.
There may also be signs of anterior uveitis, such as miosis (small
pupil), aqueous flare (protein in the aqueous humour), and redness of
the eye. An axon reflex may be responsible for uveitis formation
stimulation of pain receptors in the cornea results in release
inflammatory mediators such as prostaglandins, histamine, and
Diagnosis Diagnosis is through direct observation of the
ulcer with the use of fluorescein stain, which is taken up by exposed
corneal stroma and appears green. With descemetoceles, Descemet's
membrane will bulge forward and after staining will appear as a dark
circle with a green boundary, because it does not absorb the stain.
Other tests that may be necessary include a Schirmer's test for
keratoconjunctivitis sicca and an analysis of facial nerve function
for facial nerve paralysis.
Treatment Treatment of corneal ulcers includes topical
antibiotic therapy to prevent infection, and pain medications,
including topical atropine to stop spasms of the ciliary muscle.
Atropine may decrease tear production and interfere with corneal
healing. Superficial ulcers usually heal in less than a week. Deep
ulcers and descemetoceles may require corneal suturing, conjunctival
grafts or conjunctival flaps, soft contact lenses, or corneal
transplant. Topical corticosteroids and anesthetics should not be used
on any type of corneal ulcer because they prevent healing and will
often make them worse.
Corneal Healing An ulcer of the cornea heals by two methods:
migration of surrounding epithelial cells followed by mitosis
(dividing) of the cells, and introduction of blood vessels from the
conjunctiva. Superficial small ulcers heal rapidly by the first
method. However, larger or deeper ulcers often require the presence of
blood vessels to supply inflammatory cells. White blood cells and
fibroblasts produce granulation tissue and then scar tissue,
effectively healing the cornea.
Refractory Corneal Ulcers Refractory corneal ulcers are superficial
ulcers that heal poorly and tend to recur. They are also known as
indolent ulcers or Boxer ulcers. They are believed to be caused by a
defect in the basement membrane and a lack of hemidesmosomal
attachments. They are recognized by undermined epithelium that
surrounds the ulcer and easily peels back. Refractory corneal ulcers
are most commonly seen in middle aged or older dogs and often occur in
the other eye later.
Refractory corneal ulcers can take a long time to heal, sometimes
months. Topical antibiotics are used continually to prevent infection.
Pain medications are given as needed. Loose epithelium is removed with
a dry cotton swab under topical anesthesia. This is in order to allow
production of normal basement membrane and division of normal
epithelium. Often further treatment is necessary, such as a
keratotomy, which is superficial cutting or piercing of the cornea.
There are two main types used in dogs: multiple punctate keratotomy
(MPK) and grid keratotomy (GK). MPK involves making small superficial
punctures into the cornea with a needle. GK is more commonly used and
involves making parallel and perpendicular scratches in the corneal
surface. Usually only topical anesthesia is necessary. By scoring the
corneal surface, anchoring points are provided for attachment of new
epithelium. Of course, these procedures should only be performed by a
veterinarian, particularly one with some experience in this treatment.
Complete healing takes about three to four weeks. Keratotomies may
lead to corneal sequestration in cats. Other medications have been
shown to be useful in topical treatment of refractory ulcers,
including glycosaminoglycans such as sodium hyaluronate and
chondroitin sulfate, aminocaproic acid, and acetylcysteine.
Commonly Affected Breeds
American Cocker Spaniel
Chesapeake Bay Retriever
German Shepherd Dog
West Highland White Terrier
Wirehaired Fox Terrier
Melting Ulcers Melting ulcers are a type of corneal ulcer
involving progressive loss of stroma in a dissolving fashion. This is
most commonly seen in Pseudomonas infection, but it can be caused by
other types of bacteria or fungi. These infectious agents produce
proteases and collagenases which break down the corneal stroma.
Complete loss of the stroma can occur within 24 hours. Treatment
includes antibiotics and collagenase inhibitors such as acetylcysteine
and blood serum. Surgery may be necessary.