The Cornea and Corneal Disease
What is the cornea?
The cornea is the eye's
outermost layer. It is the clear, dome-shaped surface that covers the front of
the eye.
 Structure of the cornea
Although the cornea is clear and seems to lack substance, it is actually a
highly organized group of cells and proteins. Unlike most tissues in the body,
the cornea contains no blood vessels to nourish or protect it against infection.
Instead, the cornea receives its nourishment from the tears and aqueous humor
that fills the chamber behind it. The cornea must remain transparent to refract
light properly, and the presence of even the tiniest blood vessels can interfere
with this process. To see well, all layers of the cornea must be free of any
cloudy or opaque areas.
The corneal tissue is arranged in five basic layers, each having an important
function. These five layers are:
Epithelium
The epithelium is the cornea's outermost region, comprising about 10
percent of the tissue's thickness. The epithelium functions primarily to: (1)
Block the passage of foreign material, such as dust, water, and bacteria, into
the eye and other layers of the cornea; and (2) Provide a smooth surface that
absorbs oxygen and cell nutrients from tears, then distributes these nutrients
to the rest of the cornea. The epithelium is filled with thousands of tiny
nerve endings that make the cornea extremely sensitive to pain when rubbed or
scratched. The part of the epithelium that serves as the foundation on which
the epithelial cells anchor and organize themselves is called the basement
membrane.
Bowman's layer
Lying directly below the basement membrane of the epithelium is a
transparent sheet of tissue known as Bowman's layer. It is composed of strong
layered protein fibers called collagen. Once injured, Bowman's layer can form
a scar as it heals. If these scars are large and centrally located, some
vision loss can occur.
Stroma
Beneath Bowman's layer is the stroma, which comprises about 90 percent of
the cornea's thickness. It consists primarily of water (78 percent) and
collagen (16 percent), and does not contain any blood vessels. Collagen gives
the cornea its strength, elasticity, and form. The collagen's unique shape,
arrangement, and spacing are essential in producing the cornea's
light-conducting transparency.
Descemet's membrane
Under the stroma is Descemet's membrane, a thin but strong sheet of tissue
that serves as a protective barrier against infection and injuries. Descemet's
membrane is composed of collagen fibers (different from those of the stroma)
and is made by the endothelial cells that lie below it. Descemet's membrane is
regenerated readily after injury.
Endothelium
The endothelium is the extremely thin, innermost layer of the cornea.
Endothelial cells are essential in keeping the cornea clear. Normally, fluid
leaks slowly from inside the eye into the middle corneal layer (stroma). The
endothelium's primary task is to pump this excess fluid out of the stroma.
Without this pumping action, the stroma would swell with water, become hazy,
and ultimately opaque. In a healthy eye, a perfect balance is maintained
between the fluid moving into the cornea and fluid being pumped out of the
cornea. Once endothelium cells are destroyed by disease or trauma, they are
lost forever. If too many endothelial cells are destroyed, corneal edema and
blindness ensue, with corneal transplantation the only available therapy.
Refractive errors
About 120 million people in the United States wear eyeglasses or contact
lenses to correct nearsightedness, farsightedness, or astigmatism. These vision
disorders--called refractive errors-- affect the cornea and are the most common
of all vision problems in this country.
Refractive errors occur when the curve of the cornea is irregularly shaped
(too steep or too flat). When the cornea is of normal shape and curvature, it
bends, or refracts, light on the retina with precision. However, when the curve
of the cornea is irregularly shaped, the cornea bends light imperfectly on the
retina. This affects good vision. The refractive process is similar to the way a
camera takes a picture. The cornea and lens in your eye act as the camera lens.
The retina is similar to the film. If the image is not focused properly, the
film (or retina) receives a blurry image. The image that your retina
"sees" then goes to your brain, which tells you what the image is.
When the cornea is curved too much, or if the eye is too long, faraway
objects will appear blurry because they are focused in front of the retina. This
is called myopia, or nearsightedness. Myopia affects over 25 percent of all
adult Americans.
Hyperopia, or farsightedness, is the opposite of myopia. Distant objects are
clear, and close-up objects appear blurry. With hyperopia, images focus on a
point beyond the retina. Hyperopia results from an eye that is too short.
Astigmatism is a condition in which the uneven curvature of the cornea blurs
and distorts both distant and near objects. A normal cornea is round, with even
curves from side to side and top to bottom. With astigmatism, the cornea is
shaped more like the back of a spoon, curved more in one direction than in
another. This causes light rays to have more than one focal point and focus on
two separate areas of the retina, distorting the visual image. Two-thirds of
Americans with myopia also have astigmatism.
Refractive errors are usually corrected by eyeglasses or contact lenses.
Although these are safe and effective methods for treating refractive errors,
refractive surgeries are becoming an increasingly popular option.
What is the function of the cornea?
Because the cornea is as smooth and clear as glass but is strong and durable,
it helps the eye in two ways:
- It helps to shield the rest of the eye from germs, dust, and other harmful
matter. The cornea shares this protective task with the eyelids, the eye
socket, tears, and the sclera, or white part of the eye.
- The cornea acts as the eye's outermost lens. It functions like a window
that controls and focuses the entry of light into the eye. The cornea
contributes between 65-75 percent of the eye's total focusing power.
When light strikes the cornea, it bends--or refracts--the incoming light onto
the lens. The lens further refocuses that light onto the retina, a layer of
light sensing cells lining the back of the eye that starts the translation of
light into vision. For you to see clearly, light rays must be focused by the
cornea and lens to fall precisely on the retina. The retina converts the light
rays into impulses that are sent through the optic nerve to the brain, which
interprets them as images.
The refractive process is similar to the way a camera takes a picture. The
cornea and lens in the eye act as the camera lens. The retina is similar to the
film. If the image is not focused properly, the film (or retina) receives a
blurry image.
The cornea also serves as a filter, screening out some of the most damaging
ultraviolet (UV) wavelengths in sunlight. Without this protection, the lens and
the retina would be highly susceptible to injury from UV radiation.
How does the cornea respond to injury?
The cornea copes very well with minor injuries or abrasions. If the highly
sensitive cornea is scratched, healthy cells slide over quickly and patch the
injury before infection occurs and vision is affected. If the scratch penetrates
the cornea more deeply, however, the healing process will take longer, at times
resulting in greater pain, blurred vision, tearing, redness, and extreme
sensitivity to light. These symptoms require professional treatment. Deeper
scratches can also cause corneal scarring, resulting in a haze on the cornea
that can greatly impair vision. In this case, a corneal transplant may be
needed.
What are some diseases and disorders affecting the cornea?
Some diseases and disorders of the cornea are:
Allergies. Allergies affecting the eye are fairly
common. The most common allergies are those related to pollen, particularly
when the weather is warm and dry. Symptoms can include redness, itching,
tearing, burning, stinging, and watery discharge, although they are not
usually severe enough to require medical attention. Antihistamine
decongestant eyedrops can effectively reduce these symptoms, as does rain
and cooler weather, which decreases the amount of pollen in the air.
An increasing number of eye allergy cases are related to medications and
contact lens wear. Also, animal hair and certain cosmetics, such as mascara,
face creams, and eyebrow pencil, can cause allergies that affect the eye.
Touching or rubbing eyes after handling nail polish, soaps, or chemicals may
cause an allergic reaction. Some people have sensitivity to lip gloss and
eye makeup. Allergy symptoms are temporary and can eliminated by not having
contact with the offending cosmetic or detergent.
Conjunctivitis (Pink Eye). This term describes a
group of diseases that cause swelling, itching, burning, and redness of the
conjunctiva, the protective membrane that lines the eyelids and covers
exposed areas of the sclera, or white of the eye. Conjunctivitis can spread
from one person to another and affects millions of Americans at any given
time. Conjunctivitis can be caused by a bacterial or viral infection,
allergy, environmental irritants, a contact lens product, eyedrops, or eye
ointments.
At its onset, conjunctivitis is usually painless and does not adversely
affect vision. The infection will clear in most cases without requiring
medical care. But for some forms of conjunctivitis, treatment will be
needed. If treatment is delayed, the infection may worsen and cause corneal
inflammation and a loss of vision.
Corneal infections. Sometimes the cornea is damaged
after a foreign object has penetrated the tissue, such as from a poke in the
eye. At other times, bacteria or fungi from a contaminated contact lens can
pass into the cornea. Situations like these can cause painful inflammation
and corneal infections called keratitis. These infections can reduce visual
clarity, produce corneal discharges, and perhaps erode the cornea. Corneal
infections can also lead to corneal scarring, which can impair vision and
may require a corneal transplant.
As a general rule, the deeper the corneal infection, the more severe the
symptoms and complications. It should be noted that corneal infections,
although relatively infrequent, are the most serious complication of contact
lens wear.
Minor corneal infections are commonly treated with anti-bacterial eye drops.
If the problem is severe, it may require more intensive antibiotic or
anti-fungal treatment to eliminate the infection, as well as steroid eye
drops to reduce inflammation. Frequent visits to an eye care professional
may be necessary for several months to eliminate the problem.
Dry eye. The continuous production and drainage of
tears is important to the eye's health. Tears keep the eye moist, help
wounds heal, and protect against eye infection. In people with dry eye, the
eye produces fewer or less quality tears and is unable to keep its surface
lubricated and comfortable.
The tear film consists of three layers--an outer, oily (lipid) layer that
keeps tears from evaporating too quickly and helps tears remain on the eye;
a middle (aqueous) layer that nourishes the cornea and conjunctiva; and a
bottom (mucin) layer that helps to spread the aqueous layer across the eye
to ensure that the eye remains wet. As we age, the eyes usually produce
fewer tears. Also, in some cases, the lipid and mucin layers produced by the
eye are of such poor quality that tears cannot remain in the eye long enough
to keep the eye sufficiently lubricated.
The main symptom of dry eye is usually a scratchy or sandy feeling as if
something is in the eye. Other symptoms may include stinging or burning of
the eye; episodes of excess tearing that follow periods of very dry
sensation; a stringy discharge from the eye; and pain and redness of the
eye. Sometimes people with dry eye experience heaviness of the eyelids or
blurred, changing, or decreased vision, although loss of vision is uncommon.
Dry eye is more common in women, especially after menopause. Surprisingly,
some people with dry eye may have tears that run down their cheeks. This is
because the eye may be producing less of the lipid and mucin layers of the
tear film, which help keep tears in the eye. When this happens, tears do not
stay in the eye long enough to thoroughly moisten it.
Dry eye can occur in climates with dry air, as well as with the use of some
drugs, including antihistamines, nasal decongestants, tranquilizers, and
anti-depressant drugs. People with dry eye should let their health care
providers know all the medications they are taking, since some of them may
intensify dry eye symptoms.
People with connective tissue diseases, such as rheumatoid arthritis, can
also develop dry eye. It is important to note that dry eye is sometimes a
symptom of Sjögren's syndrome, a disease that attacks the body's
lubricating glands, such as the tear and salivary glands. A complete
physical examination may diagnose any underlying diseases.
Artificial tears, which lubricate the eye, are the principal treatment for
dry eye. They are available over-the-counter as eye drops. Sterile ointments
are sometimes used at night to help prevent the eye from drying. Using
humidifiers, wearing wrap-around glasses when outside, and avoiding outside
windy and dry conditions may bring relief. For people with severe cases of
dry eye, temporary or permanent closure of the tear drain (small openings at
the inner corner of the eyelids where tears drain from the eye) may be
helpful.
Fuchs' dystrophy. Fuchs' dystrophy is a slowly
progressing disease that usually affects both eyes and is slightly more
common in women than in men. Although doctors can often see early signs of
Fuchs' dystrophy in people in their 30s and 40s, the disease rarely affects
vision until people reach their 50s and 60s.
Fuchs' dystrophy occurs when endothelial cells gradually deteriorate without
any apparent reason. As more endothelial cells are lost over the years, the
endothelium becomes less efficient at pumping water out of the stroma. This
causes the cornea to swell and distort vision. Eventually, the epithelium
also takes on water, resulting in pain and severe visual impairment.
Epithelial swelling damages vision by changing the cornea's normal
curvature, and causing a sight-impairing haze to appear in the tissue.
Epithelial swelling will also produce tiny blisters on the corneal surface.
When these blisters burst, they are extremely painful.
At first, a person with Fuchs' dystrophy will awaken with blurred vision
that will gradually clear during the day. This occurs because the cornea is
normally thicker in the morning; it retains fluids during sleep that
evaporate in the tear film while we are awake. As the disease worsens, this
swelling will remain constant and reduce vision throughout the day.
When treating the disease, doctors will try first to reduce the swelling
with drops, ointments, or soft contact lenses. They also may instruct a
person to use a hair dryer, held at arm's length or directed across the
face, to dry out the epithelial blisters. This can be done two or three
times a day.
When the disease interferes with daily activities, a person may need to
consider having a corneal transplant to restore sight. The short-term
success rate of corneal transplantation is quite good for people with Fuchs'
dystrophy. However, some studies suggest that the long-term survival of the
new cornea can be a problem.
Corneal dystrophies
A corneal dystrophy is a condition in which one or more parts of the
cornea lose their normal clarity due to a buildup of cloudy material. There are
over 20 corneal dystrophies that affect all parts of the cornea. These diseases
share many traits:
- They are usually inherited.
- They affect the right and left eyes equally.
- They are not caused by outside factors, such as injury or diet.
- Most progress gradually.
- Most usually begin in one of the five corneal layers and may later spread
to nearby layers.
- Most do not affect other parts of the body, nor are they related to
diseases affecting other parts of the eye or body.
- Most can occur in otherwise totally healthy people, male or female.
Corneal dystrophies affect vision in widely differing ways. Some cause severe
visual impairment, while a few cause no vision problems and are discovered
during a routine eye examination. Other dystrophies may cause repeated episodes
of pain without leading to permanent loss of vision.
Some of the most common corneal dystrophies include Fuchs' dystrophy,
keratoconus, lattice dystrophy, and map-dot-fingerprint dystrophy.
Herpes Zoster (Shingles). This infection is produced by the varicella-zoster
virus, the same virus that causes chickenpox. After an initial outbreak of
chickenpox (often during childhood), the virus remains inactive within the nerve
cells of the central nervous system. But in some people, the varicella-zoster
virus will reactivate at another time in their lives. When this occurs, the
virus travels down long nerve fibers and infects some part of the body,
producing a blistering rash (shingles), fever, painful inflammations of the
affected nerve fibers, and a general feeling of sluggishness.
Varicella-zoster virus may travel to the head and neck, perhaps involving an
eye, part of the nose, cheek, and forehead. In about 40 percent of those with
shingles in these areas, the virus infects the cornea. Doctors will often
prescribe oral anti-viral treatment to reduce the risk of the virus infecting
cells deep within the tissue, which could inflame and scar the cornea. The
disease may also cause decreased corneal sensitivity, meaning that foreign
matter, such as eyelashes, in the eye are not felt as keenly. For many, this
decreased sensitivity will be permanent.
Although shingles can occur in anyone exposed to the varicella-zoster virus,
research has established two general risk factors for the disease: (1) Advanced
age; and (2) A weakened immune system. Studies show that people over age 80 have
a five times greater chance of having shingles than adults between the ages of
20 and 40. Unlike herpes simplex I, the varicella-zoster virus does not usually
flare up more than once in adults with normally functioning immune systems.
Be aware that corneal problems may arise months after the shingles are gone.
For this reason, it is important that people who have had facial shingles
schedule follow-up eye examinations.
Iridocorneal Endothelial Syndrome. More common in women and usually
diagnosed between ages 30-50, iridocorneal endothelial (ICE) syndrome has three
main features: (1) Visible changes in the iris, the colored part of the eye that
regulates the amount of light entering the eye; (2) Swelling of the cornea; and
(3) The development of glaucoma, a disease that can cause severe vision loss
when normal fluid inside the eye cannot drain properly. ICE is usually present
in only one eye.
ICE syndrome is actually a grouping of three closely linked conditions: iris
nevus (or Cogan-Reese) syndrome; Chandler's syndrome; and essential
(progressive) iris atrophy (hence the acronym ICE). The most common feature of
this group of diseases is the movement of endothelial cells off the cornea onto
the iris. This loss of cells from the cornea often leads to corneal swelling,
distortion of the iris, and variable degrees of distortion of the pupil, the
adjustable opening at the center of the iris that allows varying amounts of
light to enter the eye. This cell movement also plugs the fluid outflow channels
of the eye, causing glaucoma.
The cause of this disease is unknown. While we do not yet know how to keep
ICE syndrome from progressing, the glaucoma associated with the disease can be
treated with medication, and a corneal transplant can treat the corneal
swelling.
Keratoconus. This disorder--a progressive thinning of the cornea--is the
most common corneal dystrophy in the U.S., affecting one in every 2000
Americans. It is more prevalent in teenagers and adults in their 20s.
Keratoconus arises when the middle of the cornea thins and gradually bulges
outward, forming a rounded cone shape. This abnormal curvature changes the
cornea's refractive power, producing moderate to severe distortion (astigmatism)
and blurriness (nearsightedness) of vision. Keratoconus may also cause swelling
and a sight-impairing scarring of the tissue.
Studies indicate that keratoconus stems from one of several possible causes:
- An inherited corneal abnormality. About seven percent of those with the
condition have a family history of keratoconus.
- An eye injury, i.e., excessive eye rubbing or wearing hard contact lenses
for many years.
- Certain eye diseases, such as retinitis pigmentosa, retinopathy of
prematurity, and vernal keratoconjunctivitis.
- Systemic diseases, such as Leber's congenital amaurosis, Ehlers-Danlos
syndrome, Down syndrome, and osteogenesis imperfecta.
Keratoconus usually affects both eyes. At first, people can correct their
vision with eyeglasses. But as the astigmatism worsens, they must rely on
specially fitted contact lenses to reduce the distortion and provide better
vision. Although finding a comfortable contact lens can be an extremely
frustrating and difficult process, it is crucial because a poorly fitting lens
could further damage the cornea and make wearing a contact lens intolerable.
In most cases, the cornea will stabilize after a few years without ever
causing severe vision problems. But in about 10 to 20 percent of people with
keratoconus, the cornea will eventually become too scarred or will not tolerate
a contact lens. If either of these problems occur, a corneal transplant may be
needed. This operation is successful in more than 90 percent of those with
advanced keratoconus. Several studies have also reported that 80 percent or more
of these patients have 20/40 vision or better after the operation.
The National Eye Institute is conducting a natural history study--called the Collaborative
Longitudinal Evaluation of Keratoconus Study--to identify factors that
influence the severity and progression of keratoconus.
Lattice dystrophy. Lattice dystrophy gets its name from an accumulation
of amyloid deposits, or abnormal protein fibers, throughout the middle and
anterior stroma. During an eye examination, the doctor sees these deposits in
the stroma as clear, comma-shaped overlapping dots and branching filaments,
creating a lattice effect. Over time, the lattice lines will grow opaque and
involve more of the stroma. They will also gradually converge, giving the cornea
a cloudiness that may also reduce vision.
In some people, these abnormal protein fibers can accumulate under the
cornea's outer layer--the epithelium. This can cause erosion of the epithelium.
This condition is known as recurrent epithelial erosion. These erosions: (1)
Alter the cornea's normal curvature, resulting in temporary vision problems; and
(2) Expose the nerves that line the cornea, causing severe pain. Even the
involuntary act of blinking can be painful.
To ease this pain, a doctor may prescribe eye drops and ointments to reduce
the friction on the eroded cornea. In some cases, an eye patch may be used to
immobilize the eyelids. With effective care, these erosions usually heal within
three days, although occasional sensations of pain may occur for the next
six-to-eight weeks.
By about age 40, some people with lattice dystrophy will have scarring under
the epithelium, resulting in a haze on the cornea that can greatly obscure
vision. In this case, a corneal transplant may be needed. Although people with
lattice dystrophy have an excellent chance for a successful transplant, the
disease may also arise in the donor cornea in as little as three years. In one
study, about half of the transplant patients with lattice dystrophy had a
recurrence of the disease from between two to 26 years after the operation. Of
these, 15 percent required a second corneal transplant. Early lattice and
recurrent lattice arising in the donor cornea responds well to treatment with
the excimer laser.
Although lattice dystrophy can occur at any time in life, the condition
usually arises in children between the ages of two and seven.
Map-Dot-Fingerprint dystrophy. This dystrophy occurs when the
epithelium's basement membrane develops abnormally (the basement membrane serves
as the foundation on which the epithelial cells, which absorb nutrients from
tears, anchor and organize themselves). When the basement membrane develops
abnormally, the epithelial cells cannot properly adhere to it. This, in turn,
causes recurrent epithelial erosions, in which the epithelium's outermost layer
rises slightly, exposing a small gap between the outermost layer and the rest of
the cornea.
Epithelial erosions can be a chronic problem. They may alter the cornea's
normal curvature, causing periodic blurred vision. They may also expose the
nerve endings that line the tissue, resulting in moderate to severe pain lasting
as long as several days. Generally, the pain will be worse on awakening in the
morning. Other symptoms include sensitivity to light, excessive tearing, and
foreign body sensation in the eye.
Map-dot-fingerprint dystrophy, which tends to occur in both eyes, usually
affects adults between the ages of 40 and 70, although it can develop earlier in
life. Also known as epithelial basement membrane dystrophy, map-dot-fingerprint
dystrophy gets its name from the unusual appearance of the cornea during an eye
examination. Most often, the affected epithelium will have a map-like
appearance, i.e., large, slightly gray outlines that look like a continent on a
map. There may also be clusters of opaque dots underneath or close to the
map-like patches. Less frequently, the irregular basement membrane will form
concentric lines in the central cornea that resemble small fingerprints.
Typically, map-dot-fingerprint dystrophy will flare up occasionally for a few
years and then go away on its own, with no lasting loss of vision. Most people
never know that they have map-dot-fingerprint dystrophy, since they do not have
any pain or vision loss. However, if treatment is needed, doctors will try to
control the pain associated with the epithelial erosions. They may patch the eye
to immobilize it, or prescribe lubricating eye drops and ointments. With
treatment, these erosions usually heal within three days, although periodic
flashes of pain may occur for several weeks thereafter. Other treatments include
anterior corneal punctures to allow better adherence of cells; corneal scraping
to remove eroded areas of the cornea and allow regeneration of healthy
epithelial tissue; and use of the excimer laser to remove surface
irregularities.
Ocular Herpes. Herpes of the eye, or ocular herpes, is a recurrent viral
infection that is caused by the herpes simplex virus and is the most common
infectious cause of corneal blindness in the U.S. Previous studies show that
once people develop ocular herpes, they have up to a 50 percent chance of having
a recurrence. This second flare-up could come weeks or even years after the
initial occurrence.
Ocular herpes can produce a painful sore on the eyelid or surface of the eye
and cause inflammation of the cornea. Prompt treatment with anti-viral drugs
helps to stop the herpes virus from multiplying and destroying epithelial cells.
However, the infection may spread deeper into the cornea and develop into a more
severe infection called stromal keratitis, which causes the body's immune system
to attack and destroy stromal cells. Stromal keratitis is more difficult to
treat than less severe ocular herpes infections. Recurrent episodes of stromal
keratitis can cause scarring of the cornea, which can lead to loss of vision and
possibly blindness.
Like other herpetic infections, herpes of the eye can be controlled. An
estimated 400,000 Americans have had some form of ocular herpes. Each year,
nearly 50,000 new and recurring cases are diagnosed in the United States, with
the more serious stromal keratitis accounting for about 25 percent. In one large
study, researchers found that recurrence rate of ocular herpes was 10 percent
within one year, 23 percent within two years, and 63 percent within 20 years.
Some factors believed to be associated with recurrence include fever, stress,
sunlight, and eye injury.
The National Eye Institute supported the Herpetic Eye Disease Study, a group
of clinical trials that studied various treatments for severe ocular herpes.
Pterygium. A pterygium is a pinkish, triangular-shaped tissue growth on
the cornea. Some pterygia grow slowly throughout a person's life, while others
stop growing after a certain point. A pterygium rarely grows so large that it
begins to cover the pupil of the eye.
Pterygia are more common in sunny climates and in the 20-40 age group.
Scientists do not know what causes pterygia to develop. However, since people
who have pterygia usually have spent a significant time outdoors, many doctors
believe ultraviolet (UV) light from the sun may be a factor. In areas where
sunlight is strong, wearing protective eyeglasses, sunglasses, and/or hats with
brims are suggested. While some studies report a higher prevalence of pterygia
in men than in women, this may reflect different rates of exposure to UV light.
Because a pterygium is visible, many people want to have it removed for
cosmetic reasons. It is usually not too noticeable unless it becomes red and
swollen from dust or air pollutants. Surgery to remove a pterygium is not
recommended unless it affects vision. If a pterygium is surgically removed, it
may grow back, particularly if the patient is less than 40 years of age.
Lubricants can reduce the redness and provide relief from the chronic
irritation.
Stevens-Johnson Syndrome. Stevens-Johnson Syndrome (SJS), also called
erythema multiforme major, is a disorder of the skin that can also affect the
eyes. SJS is characterized by painful, blistery lesions on the skin and the
mucous membranes (the thin, moist tissues that line body cavities) of the mouth,
throat, genital region, and eyelids. SJS can cause serious eye problems, such as
severe conjunctivitis; iritis, an inflammation inside the eye; corneal blisters
and erosions; and corneal holes. In some cases, the ocular complications from
SJS can be disabling and lead to severe vision loss.
Scientists are not certain why SJS develops. The most commonly cited cause of
SJS is an adverse allergic drug reaction. Almost any drug--but most particularly
sulfa drugs--can cause SJS. The allergic reaction to the drug may not occur
until 7-14 days after first using it. SJS can also be preceded by a viral
infection, such as herpes or the mumps, and its accompanying fever, sore throat,
and sluggishness. Treatment for the eye may include artificial tears,
antibiotics, or corticosteroids. About one-third of all patients diagnosed with
SJS have recurrences of the disease.
SJS occurs twice as often in men as women, and most cases appear in children
and young adults under 30, although it can develop in people at any age.
What is a corneal transplant? Is it safe?
A corneal transplant involves replacing a diseased or scarred cornea with a
new one. When the cornea becomes cloudy, light cannot penetrate the eye to reach
the light-sensitive retina. Poor vision or blindness may result.
In corneal transplant surgery, the surgeon removes the central portion of the
cloudy cornea and replaces it with a clear cornea, usually donated through an
eye bank. A trephine, an instrument like a cookie cutter, is used to remove the
cloudy cornea. The surgeon places the new cornea in the opening and sews it with
a very fine thread. The thread stays in for months or even years until the eye
heals properly (removing the thread is quite simple and can easily be done in an
ophthalmologist's office). Following surgery, eye drops to help promote healing
will be needed for several months.
Corneal transplants are very common in the United States; about 40,000 are
performed each year. The chances of success of this operation have risen
dramatically because of technological advances, such as less irritating sutures,
or threads, which are often finer than a human hair; and the surgical
microscope. Corneal transplantation has restored sight to many, who a generation
ago would have been blinded permanently by corneal injury, infection, or
inherited corneal disease or degeneration.
What problems can develop from a corneal transplant?
Even with a fairly high success rate, some problems can develop, such as
rejection of the new cornea. Warning signs for rejection are decreased vision,
increased redness of the eye, increased pain, and increased sensitivity to
light. If any of these last for more than six hours, you should immediately call
your ophthalmologist. Rejection can be successfully treated if medication is
administered at the first sign of symptoms.
A study supported by the National Eye Institute (NEI) suggests that matching
the blood type, but not tissue type, of the recipient with that of the cornea
donor may improve the success rate of corneal transplants in people at high risk
for graft failure. Approximately 20 percent of corneal transplant
patients--between 6000-8000 a year--reject their donor corneas. The NEI-supported
study, called the Collaborative
Corneal Transplantation Study, found that high-risk patients may reduce the
likelihood of corneal rejection if their blood types match those of the cornea
donors. The study also concluded that intensive steroid treatment after
transplant surgery improves the chances for a successful transplant.
Are there alternatives to a corneal transplant?
Phototherapeutic keratectomy (PTK) is one of the latest advances in eye care
for the treatment of corneal dystrophies, corneal scars, and certain corneal
infections. Only a short time ago, people with these disorders would most likely
have needed a corneal transplant. By combining the precision of the excimer
laser with the control of a computer, doctors can vaporize microscopically thin
layers of diseased corneal tissue and etch away the surface irregularities
associated with many corneal dystrophies and scars. Surrounding areas suffer
relatively little trauma. New tissue can then grow over the now-smooth surface.
Recovery from the procedure takes a matter of days, rather than months as with a
transplant. The return of vision can occur rapidly, especially if the cause of
the problem is confined to the top layer of the cornea. Studies have shown close
to an 85 percent success rate in corneal repair using PTK for well-selected
patients.
The Excimer laser
One of the technologies developed to treat corneal disease is the excimer
laser. This device emits pulses of ultraviolet light--a laser beam--to etch away
surface irregularities of corneal tissue. Because of the laser's precision,
damage to healthy, adjoining tissue is reduced or eliminated.
The PTK procedure is especially useful for people with inherited disorders,
whose scars or other corneal opacities limit vision by blocking the way images
form on the retina. PTK has been approved by the U.S. Food and Drug
Administration.
Current Corneal research
Vision research funded by the National Eye Institute (NEI) is leading to
progress in understanding and treating corneal disease.
For example, scientists are learning how transplanting corneal cells from a
patient's healthy eye to the diseased eye can treat certain conditions that
previously caused blindness. Vision researchers continue to investigate ways to
enhance corneal healing and eliminate the corneal scarring that can threaten
sight. Also, understanding how genes produce and maintain a healthy cornea will
help in treating corneal disease.
Genetic studies in families afflicted with corneal dystrophies have yielded
new insight into 13 different corneal dystrophies, including keratoconus. To
identify factors that influence the severity and progression of keratoconus, the
NEI is conducting a natural history study--called the Collaborative
Longitudinal Evaluation of Keratoconus (CLEK) Study--that is following more
than 1200 patients with the disease. Scientists are looking for answers to how
rapidly their keratoconus will progress, how bad their vision will become, and
whether they will need cornealsurgery to treat it. Results from the CLEK Study
will enable eye care practitioners to better manage this complex disease.
The NEI also supported the Herpetic
Eye Disease Study (HEDS), a group of clinical trials that studied various
treatments for severe ocular herpes. HEDS researchers reported that oral
acyclovir reduced by 41 percent the chance that ocular herpes, a recurrent
disease, would return. The study clearly showed that acyclovir therapy can
benefit people with all forms of ocular herpes. Current HEDS research is
examining the role of psychological stress and other factors as triggers of
ocular herpes recurrences.
For more information about the NEI or NEI sponsored clinical trials, contact
the:
National Eye Institute
Building 31, Room 6A32
31 Center Drive, MSC 2510
Bethesda, MD 20892-2510
Telephone: (301) 496-5248
Website: http://www.nei.nih.gov
E-Mail: 2020@nei.nih.gov
Other information sources
Cornea Research Foundation of America
9002 N. Meridian Street, Suite 212
Indianapolis, IN 46260
(317) 844-5610
http://www.cornea.org
National Keratoconus Foundation
8733 Beverly Blvd., Suite 201
Los Angeles, CA 90048
1-800-521-2524
(310) 423-6455
http://www.nkcf.org
Sjögren's Syndrome Foundation (SSF)
8120 Woodmont Avenue, Suite 530
Bethesda, MD 20814
1-800-475-6473
(301) 718-0300
http://www.sjogrens.org
Stevens Johnson Syndrome Foundation
P.O. Box 350333
Westminster, CO 80030
(303) 635-1241
http://www.sjsupport.org
Source: National Institutes of Health; National Eye Institute
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