If the cornea of your eye becomes damaged
through disease, infection, or injury, the resulting scars can interfere with
vision by blocking or distorting light as it enters the eye.
The cornea is the clear, protective outer
layer of the eye.It forms 1/6 th of the outer layer of the eye.It is the front
most (anterior) part of the eye. Along with the sclera (white of the eye), it
serves as a barrier against dirt, germs, and other particles that can harm the
eye's delicate components. The cornea is also capable of filtering out some
amounts of the sun's ultraviolet light.
The cornea also plays a key role in vision. As
light enters the eye, it is refracted, or bent, by the outside shape of the
cornea. The curvature of this outer layer helps determine how well your eye can
focus on objects close-up and far away.
There are three main layers of the cornea:
·
Epithelium. The most superficial
layer of the cornea, the epithelium stops outside matter from entering the eye.
This layer of the cornea also absorbs oxygen and nutrients from tears.
·
Bowmans membrane . connective
tissue
·
Stroma. The stroma is the
middle and thickest layer of the cornea and is found behind the
epithelium. It is made up mostly of water and proteins that give it an elastic
but solid form.
·
Descemets membrane.supports
endothelium.
·
Endothelium. The endothelium is a
single layer of cells located between the stroma and the aqueous humor -- the
clear fluid found in the front chamber of the eye. The endothelium works as a
pump, expelling excess water back into the eye as it is absorbed into the
stroma. Without this specialized function, the stroma would become waterlogged,
creating a hazy and opaque cornea and reducing vision.It is very
critical and needs to be taken care of during any intraocular surgery.
The term "corneal
disease" refers to a variety of conditions that affect mainly the cornea.
These include infections, degenerations, and many other disorders of the cornea
that may arise mostly as a result of heredity.
With its ability for quick
repair, the cornea usually heals after most minor injuries or infections.
However, during the healing process a variety of symptoms may be experienced,
including:
·
Pain
·
Blurred vision
·
Tearing
·
Redness
·
Extreme sensitivity to light
Although these symptoms may occur with many
other types of eye problems, they may indicate a more serious problem or
require special treatment. Therefore, if you experience any of these symptoms,
seek care from an eye doctor.
What Conditions Can Damage the Cornea?
Keratitis
Keratitis is an inflammation of the
cornea that sometimes occurs with infection after viruses, bacteria, or fungi
enter the cornea. These microorganisms can enter the eye after superficial or
deep injuries, causing infection, inflammation, and ulceration of the cornea.
Though uncommon, this type of infection can also arise after injury from
wearing contact lenses.
Symptoms of keratitis include:
·
Severe pain
·
Blurred vision
·
Tearing
·
Redness
·
Extreme sensitivity to light
·
Discharge
Treatment usually includes antibiotic or
antifungal eye drops. Sometimes, antiviral drugs and steroid eye drops are necessary.
Do not use any eye drops without consulting an eye doctor.
Ocular Herpes (Herpes of the Eye)
Herpes is a viral infection of the eye,
that may, like fever blisters, recur. The main cause of ocular herpes is the
herpes simplex virus I (HSV I), the same virus that causes cold sores, but it
can also result from the sexually transmitted herpes simplex virus II (HSV II)
that causes genital herpes.
Ocular herpes produces sores on the
surface of the cornea and, in time, the inflammation can spread deeper into the
cornea and eye.
There is no cure for ocular herpes, but
it can often be controlled with the use of antiviral drugs or steroid eye
drops.
Herpes Zoster (Shingles)
Shingles is a recurrence of the
chickenpox virus in people who have already had the disease. After a bout of
chickenpox, this virus usually remains inactive within the nerves of the body.
It can later travel down these nerves, infecting specific parts of the body,
like the eye. Herpes zoster can cause lesions on the cornea. Corneal lesions
usually heal by themselves, but antiviral treatment and/or topical steroid eye
drops may reduce the inflammation.
Shingles can occur in anyone exposed to
the chickenpox virus, but there is an increased risk in:
·
Older adults, especially
over age 80
·
People with a weakened
immune system
See your doctor if you have any symptoms
of shingles.
Corneal Degenerations
There are several types of corneal
degenerations, diseases that can cause progressive structural problems with the
cornea including:
·
Keratoconus
Keratoconus is a progressive disease in which the cornea thins
due to biomechanical weakening and
changes shape. Sometimes occurring as early as adolescence, this disease
changes the curvature of the cornea, creating either mild or severe distortion,
called astigmatism, and usually
nearsightedness. Keratoconus may also result in swelling and scarring of the
cornea and vision loss.
Factors associated with keratoconus include:
·
Genetics (a person can
inherit a tendency for the condition from a parent)
·
Eye trauma (for example,
from extensive rubbing of the eyes)
·
Associated with Eye
diseases, such as retinitis pigmentosa, retinopathy of prematurity, vernal
keratoconjuncitivitis
·
Other diseases, like Down
syndrome, osteogenesis imperfecta, Addison's disease, Leber's congenital
amaurosis, and Ehlers-Danlos syndrome
At first, keratoconus can be corrected with glasses or soft
contact lenses. But, as the disease progresses, you may need to wear rigid gas
permeable contact lenses. In approximately 10% to 15% of patients with
keratoconus, a corneal transplant may also be necessary.
During a corneal transplant, the damaged cornea is replaced with
a donated cornea. This operation is successful in about nine out of 10 people
with advanced keratoconus. Even after a transplant, you will still most likely
need glasses or contact lenses to see clearly.
What Conditions Can
Damage the Cornea? continued...
Corneal Dystrophies
There are more than 20 corneal dystrophies,
diseases that can cause structural problems with the cornea. Some of the most
common are:
·
Map-Dot-Fingerprint Dystrophy
Map-dot-fingerprint dystrophy is the abnormal appearance of the
basement membrane of the epithelium of the cornea. As this membrane that
separates the epithelium and stroma grows irregularly (thicker in some places,
thinner in others), irregularities in the cornea appear, resembling maps, dots,
and small fingerprints.
Map-dot-fingerprint dystrophy usually affects adults over age
40. It is usually painless and causes no vision loss, and can improve without
treatment. In some cases, however, epithelial erosion may occur. Epithelial
erosion can expose the nerves lining the cornea, causing severe pain,
particularly when awakening in the morning. The cornea's normal curvature may
be altered causing astigmatism and nearsightedness/farsightedness.
As the cornea is altered, vision may be blurry and accompanied
by:
·
Moderate to severe pain
·
Increased sensitivity to light
·
Excessive tearing
·
A feeling that something is in your eye
Treatment may include
an eye patch, a bandage soft contact lens, eye drops, ointments, or removal of
the loose abrading corneal epithelium as an “in-office” minor procedure.
Fuchs' Dystrophy
Fuchs' dystrophy is an inherited condition in which there is
gradual deterioration of endothelial cells. As these cells decrease in number
and function over time, the cornea is less capable of removing water from the
stroma, causing it to swell and distort vision. Haze and small blisters on the
corneal surface may also appear.
As a slowly progressing disease, signs of Fuchs' dystrophy begin
to appear in people 30 to 40 years of age, but it doesn't normally affect
vision until about 20 years later. It is more common in women than in men.
An early sign of Fuchs' dystrophy includes waking up with
blurred vision that gradually clears up during the day. As the disease worsens,
swelling becomes more consistent and vision blurs.this condition may be
associated with glaucoma.
Treatment options include:
·
Eye drops/ointments
·
Corneal transplant (full or partial)
What Conditions Can Damage the Cornea? continued...
Lattice Dystrophy
Lattice dystrophy is characterized by the presence of abnormal
protein fibers throughout the stroma. Although this condition can occur at any
age, early changes can be seen in childhood.
Lattice dystrophy gets its name from the clear overlapping lines
of proteins in the stroma. This can make the cornea cloudy and reduce vision.
In some people, these proteins may cause epithelial erosion.
Treatment of lattice dystrophy includes:
·
Prescription eye drops
·
Ointments
·
Eye patching
·
Corneal transplant
Symptoms may disappear with treatment, but a corneal transplant
may be required. Although results of this surgery are very good, lattice
dystrophy may reappear in transplant patients.
How Are Cornea Problems Diagnosed?
Cornea problems can only be diagnosed after a thorough exam by
an eye doctor.
Can Cornea Problems Be Prevented?
Infectious corneal disease caused from bacteria and viruses can
be prevented by protecting the eye from injury and limiting physical contact
with people who have contagious forms of conjunctivitis.
Avoid sharing eye makeup, contact lens solution, contact lens cases, and eye
drops with people who are infected, and wash your hands thoroughly with soap
and warm water for at least 15 seconds after contact with an infected person.
Also, following strict guidelines for contact lens hygiene can help decrease
the risk of corneal infections related to contact lens use.
Although
corneal disease resulting from hereditary factors (like dystrophies) cannot be
prevented, vision can be preserved with early detection and treatment.