Site owned by Pedernales Veterinary
Center all rights ® 2009
Site last updated on:07/09/2011
Design by: Comfort Webs.com
Issues with website please contact
webmaster: linda@comfortwebs.com
Name
Corneal Ulcers, Canine and Feline
Short Description
Corneal ulcer, descemetocele
Affected Animals: Any animal may develop a corneal ulcer. Recurrent
ulcers and refractory ones that do not heal properly occur more
commonly in middle-aged and older dogs. Cats are susceptible to
herpesvirus infection and secondary ulceration of the cornea.
Overview: The cornea is the multi-layered
transparent part of the front of the eye. It plays a vital role in
vision. Injury, bacterial, fungal, and viral infection, diseases of
the eye and eyelid, and a number of other conditions can cause the
cornea to ulcerate. A corneal ulcer can develop serious
complications that may compromise visual acuity and even result in
loss of sight if not promptly treated by a veterinarian.
A corneal ulcer is a defect or cavity in the two surface layers of
the cornea and in a variable portion of its deeper layers. Virtually
all injuries to the cornea are painful, even mild, superficial
scratches or abrasions that only involve the surface layer. The
deeper the ulcer -- the more layers that are missing -- the more
painful the ulcer will be. Deeper ulcers also carry a greater risk
for serious complications. During the healing process, blood vessel
migration across the ulcer from the outer rim of the cornea and scar
formation within the defect may impair the cornea's natural
transparency. As a result, the affected animal may experience loss
of visual acuity or even sightedness in the affected eye.
Treatment depends on the depth of the ulcer and on any associated
complications that may be present. Minor scratches, abrasions and
very superficial ulcers may be treated with antibiotics to eliminate
or prevent infection. Atropine, a pupillary dilating medication may
be given to relieve ulcer-associated eye spasm and reduce the
tendency for adhesions between the cornea and the iris to form.
Deeper corneal ulcers often require surgery to treat the ulcer and
prevent possible blindness.
Clinical Signs: Although the cornea lacks the presence of blood
vessels, it is well equipped with nerves to detect pain. Even the
slightest injury will provoke considerable discomfort. Other signs
of corneal ulcer include blepharospasm, epiphora, purulent ocular
discharge, and photophobia.
Symptoms: Common symptoms of corneal ulcer include pain,
squinting or blinking the affected eye, pawing or rubbing at the
eye, excessive tearing or discharge, pus, redness, and behavioral
changes such as hiding or avoiding light.
Description: The cornea, or front of the eye, has three very
important functions. It acts as a supportive barrier to keep the
internal structures in place within the eye. The cornea allows light
to pass into the eye and thus through the lens to the retina at the
back of the eye. It also bends the incoming light rays to aid the
lens in focusing the incoming light.
The cornea is composed of five microscopically identifiable layers.
From outermost to innermost, the layers are called the epithelium,
Bowman's membrane, the stroma, Descemet's membrane and the
endothelium. Bowman's membrane and Descemet's membrane are basement
membranes that support the epithelium and the endothelium,
respectively. When the cornea is injured, the extent to which these
layers are involved will determine the severity of the injury, the
treatment required and the prognosis for saving the eyesight in the
injured eye.
Corneal ulcers may be graded according to the depth of the ulcer and
the corneal tissue layers lost. Corneal ulcers are superficial if
only the outer, epithelial layer and Bowman's membrane is missing.
If the ulcer also has up to one half of the underlying stroma absent
as well, the ulcer is considered shallow to moderate in depth.
Corneal ulcers with more than one half of the stroma missing are
deep ulcers.
The specific cellular events underlying the healing of corneal
wounds will depend on which layers of the cornea are denuded.
Superficial scratches of the outer layer of the cornea, or
epithelium, that do not penetrate deeply into this layer usually
heal without veterinary medical treatment. Healing takes two to
three days. The denuded epithelium in corneal ulcers heals by
epithelization. In this process, intact epithelial cells move to the
defect and undergo mitosis, or simple cell division, and the new
cells close the crater in the epithelial layer. This normally takes
seven to 10 days. If Bowman's membrane is also ulcerated, healing
will take longer; this basement membrane is made up of connective
tissue that takes longer to heal. A superficial ulcer generally will
heal uneventfully in several weeks if it does not become infected.
However, all corneal ulcers are susceptible to bacterial infection,
which will delay healing. Additionally, delayed healing may be
associated with increased scar formation, so veterinary treatment is
necessary to facilitate as close to ideal healing as possible.
Deeper ulcers involving the stroma will take a number of weeks to
heal. During stromal healing, blood vessels from the outer rim of
the cornea may grow on the floor of the ulcer, a process called
neovascularization. This process promotes deep healing by providing
extra nutrients to the damaged area. During this process scar tissue
will form. In some untreated ulcers the new blood vessels will
regress and eventually disappear and scar tissue will have remodeled
upon completion of healing so that vision is not impaired. However,
in many cases of untreated deep corneal ulcers, scar tissue
sufficient to severely impair vision remains. For this reason,
treatment aimed at minimizing scar formation and idealizing healing
is always indicated. Residual new blood vessels and scar tissue
potentially can result in vision impairment because these tissues
are not transparent and the normal clarity of the cornea can be
lost.
An ulcer extending to Descemet's membrane is especially dangerous.
Without the stromal layer backing it up, Descemet's membrane, can
herniate outward. Herniation of this corneal layer is called a
descemetocele. This weakened condition of these corneal layers can
result in rupture of Descemet's membrane and structural failure of
the endothelium. When this occurs, the aqueous humor -- the fluid in
the anterior chamber of the eye immediately behind the cornea --
flows out and the outer part of the eyeball collapses. This is a
surgical emergency that requires immediate attention to save the
eye.
Some corneal ulcers may be refractory to treatment or may heal, only
to re-ulcerate repeatedly. These ulcers have a defect in the
epithelial cells of the outer cornea. This defect may have a genetic
basis.
Diagnosis: A tentative diagnosis of corneal ulcer is made
based on physical examination findings correlated with the affected
animal's history. The diagnosis is confirmed with a fluorescein
test. Fluorescein eye drops are placed in the patient's affected eye
and then washed away gently with sterile saline. In the normal eye,
the stain will wash away completely. If there is an ulcer, the stain
will bind to the damaged tissue and appear as an apple-green area on
the cornea. Deeper ulcers involving Descemet's membrane often have a
dark center and do not bind fluorescein. When stained, this area of
the cornea will appear as a dark spot with an apple-green border
around it. Illumination with a Wood's lamp, or black light, can
enhance detection of fluorescein stain retention.
Once the diagnosis of a corneal ulcer has been confirmed, the
veterinarian will search for its underlying cause. The eye and
eyelids will be thoroughly examined. Tear production may be measured
to determine if tear insufficiency has contributed to the
ulceration. Bacterial cultures may be taken to determine if
infecting organisms are present in the ulcer. In cats, viral
cultures also may be collected to see if herpesvirus, typically
FHV-1, is present.
Prognosis: Dogs and cats with superficial or shallow corneal
ulcers that are treated promptly and effectively have an excellent
prognosis for a full recovery. In general, cats tend to heal faster
and have less scar formation than dogs. Because scars from healed
ulcers can obstruct vision, treatment with medications that reduce
scar and neovacularization, or new blood vessel formation, when
appropriate, can minimize visual disability.
Indolent or refractory corneal ulcers that do not heal properly are
associated with a more guarded prognosis. Recurrences are common and
complications are highly likely. Significant corneal disease and
ulceration associated with herpesvirus infections in cats are
unpredictable in their response to treatment.
Owner compliance with veterinary instructions and patience
throughout the healing process is very important and will have a
significant impact on the clinical outcome.
Transmission or Cause:Trauma is the most common
cause of corneal ulcers. Typically, cats and dogs obtain scratches
to the eyes from other animals or from tree branches. Also, a rough
particle of dirt, gravel or other material stuck under an eyelid can
damage the cornea. Other types of trauma include chemical burns from
shampoo, medicated dips, and other substances. Surrounding hair that
continually rubs the cornea, as occurs with entropion, or inverted
eyelid, or an eyelash that continually rubs the cornea, may cause
ulceration.
Keratoconjunctivitis, or "dry eye," can cause corneal ulceration. In
this condition, tear production is inadequate. As a result, the eye
can dry out and the surface layers of the cornea can break down.
Viral infectious diseases like feline herpesvirus or various
bacterial infections can cause corneal ulcers in cats.
Identification of the underlying cause of the ulcer, whenever
possible, will facilitate treatment and the prevention of recurrent
ulceration.
A structural problem at the cellular level may underlie superficial
corneal ulcers that recur or fail to heal. In these cases the
corneal epithelium is abnormal and the cornea is predisposed to
spontaneous ulceration. Both eyes of an affected animal may ulcerate
when defective corneal epithelium is present. These structural
problems are more likely to occur in middle-aged to older breed
dogs. This is especially true in the Boxer breed, which appears to
have a genetic predisposition to spontaneous corneal ulceration.
Treatment: The type of treatment the veterinarian prescribes
for the affected dog or cat will depend on the severity of the
corneal ulcer, its duration, and the suspected underlying cause.
Generally, veterinary care is focused on treating or preventing
infection, controlling pain and inflammation, preventing further
corneal damage, and minimizing the disruption of the clear cornea by
limiting scar formation.
For superficial ulcers, the use of an antibiotic ointment is very
effective in preventing bacterial infection while the eye heals.
Viral-associated corneal lesions in cats may benefit from topical
antiviral preparations, which are likely to be used for several
weeks. Fungal infections are uncommon, but when present must be
treated with specific antifungal medications for a successful
outcome.
Corneal ulcers often cause painful spasms within the eye. Topical
atropine eye drops may be used to reduce these spasms. Atropine also
dilates the pupil; in so doing, it reduces the potential for
adhesion of the iris to the cornea. Dogs and cats given this
treatment should be kept in a low-light area, since the atropine
will make the eyes very sensitive to direct sunlight.
Deeper ulcers must be treated aggressively to minimize
complications. When the ulcer involves Descemet's membrane, surgery
will be needed to place a protective graft over the ulcer. Several
surgical techniques are available. The most common type is a
conjunctival pedicle graft, in which a flap is created from the
conjunctivae, which are the thin membranes attached to the eye, and
is stitched to the edges of the ulcer. This graft protects and
supports the ulcer as it heals, and provides a blood supply to
facilitate healing. The graft is removed when sufficient healing has
occurred.
If the Descemet's membrane ruptures through all the layers of the
cornea, the fluid within the front part of the eye will leak out,
resulting in collapse of the eyeball. This is a surgical emergency
and quick action is needed if the eye is to be saved and vision
spared. Corneal ulcers that are not healing properly may
require additional treatment measures. Tissue adhesives are used to
treat selected superficial punctures, deeper ulcers that do not
appear to be healing properly and non-healing superficial corneal
ulcers. Surgical debridement, or excision, of necrotic and uneven
tissue margins on the surface of a chronic non-healing ulcer is
commonly performed to facilitate healing. Chemical debriding agents
may also be used. Multiple procedures are usually required over
several weeks to months, depending on the ulcer's progress. In many
cases systemic antibiotics in addition to topical ones are
prescribed. Drugs that promote epithelial growth and anti-proteases
that inhibit degradative enzymes may also be given.
Self-trauma can dramatically worsen any eye lesion, and most animals
will be tempted to rub or scratch the painful eye. Elizabethan
collars are often recommended to limit the possibility of such
self-trauma, especially when the dog or cat patient is unsupervised.
A dog or cat undergoing treatment for a corneal ulcer must return to
the veterinarian frequently for re-evaluation until the ulcer has
healed. Complete healing is evident when fluorescein drops placed on
the cornea no longer stain it. Complicated cases may require
referral to a veterinary ophthalmologist.
Prevention: Treating the underlying cause of viral- or
bacterial-induced ulcers of the cornea is a critical measure in
preventing recurrence. Environmental conditions conducive to eye
trauma should be modified if possible. Dogs and cats should be
prevented as much as practically possible from having access to such
environments.
