Corneal and External Diseases
 Corneal
and external diseases involve the cornea, anterior chamber of the eye,
iris, lens, conjunctiva and eyelids, including cataracts; corneal
allergies, infections and irregularities; refractive errors
(nearsightedness, farsightedness and astigmatism); conjunctivitis (pink
eye); dry eye; tear disorders; keratoconus; pterygium; endophthalmitis;
Fuch's Dystrophy and many others.
What is the cornea?
The cornea is the transparent, dome-shaped, outermost layer that covers
the iris and pupil in the front of the eye. Corneal tissue consists of
five basic layers: epithelium, Bowman's layer, stroma, Descemet's membrane
and endothelium. Although the cornea is clear, it contains 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 fill the chamber behind it.
The cornea, one of the protective layers of the eye, serves two
functions:
 First, along with the eyelid, eye socket, and sclera (white part of the
eye), and the tear film, the cornea shields the eye from dust, germs,
and other harmful matter.
- Second, as the eye's outermost lens, it is the entry point for light
into the eye. When light strikes the cornea, it bends, or refracts, the
incoming light onto the lens. The lens further refocuses the light onto
the retina, a layer of light-sensing cells lining the back of the eye.
 To see clearly, the cornea and lens must focus the light rays precisely
on the retina. This refractive process is similar to the way a camera
takes a picture. The cornea and lens in the eye act as would a camera's
lens. The retina approximates the film. If the cornea is unable to focus
the light properly, then the retina receives a blurry image.
[back to top]
What injuries, and
irregularities affect the cornea?
Some trauma, including projectile foreign bodies, lacerations and blunt
trauma can cause scarring that clouds the cornea. Hereditary conditions
including degenerations and dystrophies may also cloud the cornea. The
most common hereditary condition seen in young people is keratoconus, a
condition in which the cornea assumes a cone shape. This is common in
children with Down's syndrome and in people with allergic conjunctivitis.
These patients may be able to use contact lenses or glasses for a period
of time, but may eventually develop scarring and high astigmatism that
cannot be corrected without corneal transplantation.
Occasionally, it may become necessary to perform a corneal transplant
following cataract surgery, if bullous keratopathy occurs. Bullous
keratopathy is a condition where the endothelial cells on the back
of the
cornea decrease in number after cataract surgery. However, this
is less common today because of new techniques and improved lens design.
[back to top]
How can the cornea be damaged?
The eye surface can be severely damaged by a number of problems,
including:
- Chemical and thermal injuries
- Pathological diseases such as Stevens-Johnson syndrome and
pemphigoid
- Chronic infections or inflammations
- New tissue growths such as pterygium (thought to be related to sun
damage) and tumors
- Neurotrophic conditions (due to damage to the eye's sensory nerves)
- Rare hereditary conditions such as aniridia (congenital absence of
the iris)
These problems can result in extensive damage on the eye surface,
leading to new blood vessel formation and scarring --- damage which
results in loss of vision.
Bascom Palmer researchers are evaluating the potential of normal tears
for modulating and promoting the healing of these conditions. A full
understanding of the exact role of tears in the healing process should
lead to strategies that would speed visual recovery and increase the
percentage of patients fully satisfied after surgery.
[back to top]
What is a corneal transplant?
Corneal transplants are one of medicine's most successful transplant
operations. In the past 35 years, more than 250,000 corneal transplants
have been performed in the United States. At Bascom Palmer, more than 250
procedures are performed annually. The procedure involves removing the
cornea from the donor eye with a special instrument resembling a small
cookie cutter. The same method is used to remove the damaged cornea from
the patient's eye. The surgeon then stitches the new cornea into place.
For many individuals, a corneal transplant may be the only hope for
restored vision, and may be necessary when the cornea is cloudy or damaged
due to disease, injury, accident, or hereditary conditions. In these
situations, the cornea must be removed and replaced with healthy donor
tissue. The procedure is successful in 90 percent of cases, restoring
sight and, in some cases, even providing sight for the first time.
Members of Bascom Palmer's corneal transplant team teach patients the
acronym RSVP to alert them to potential problems. This RSVP alert is:
R: increased Redness
S: increased Sensitivity to light
V: decreased Vision
P: increased Pain
Today, regrafts are one of the most common reasons for corneal
transplants. Regrafts occur when a patient needs a second corneal
transplant because the first one was unsuccessful. Some additional reasons
include:
- Corneal ulcers, a type of infection that often leads to scarring
- Trauma
- Fuch's Dystrophy
- Damage to the epithelial layer of the cornea, through improper
cleaning and use of contact lenses. Sleeping in contact lenses leads to
a greater risk of corneal ulcers; the symptoms include eye pain,
decreased vision, and redness.
Click here more information about corneal transplants at Bascom Palmer Eye Institute
[back to top]
What advances has Bascom Palmer Eye Institute made in
corneal transplantation?
The physicians in the Corneal and External Disease Service have
developed techniques and instrumentation to make corneal transplants
safer for patients. They have developed instruments known as "trephines,"
which are used to cut donor and recipient tissues. In addition,
Bascom Palmer physicians and scientists have created special diamond
knives to be
used in surgery and have developed storage solutions to prolong
the viability of donor corneas prior to transplantation.
[back to top]
What are refractive errors?
The cornea and lens bend or refract light rays so they can be focused on
the retina, the nerve layer that lines the back of the eye. The retina
receives the picture formed by these light rays and sends the image to the
brain through the optic nerve. A refractive error means that the shape of
the eye does not allow the light to be properly refracted making images
blurry. Refractive errors include:
What is myopia (nearsightedness)?
 Myopia
(nearsightedness) occurs when light rays are focused in front of
the retina instead of directly on the retina. Myopia is a vision problem
experienced by approximately one-third of the population. When
the eyeball is too long from front to back, the image of a distant
object
focuses in
front of the retina, instead of directly on it. As a result, the
distant object appears blurred. The more myopic the eye, the closer
an object must
be before it is in sharp focus. Nearsighted
people have difficulty seeing objects at a distance, such as highway
signs, but usually can see up-close for tasks such as reading or
sewing.
Some people with myopia can use their natural nearsightedness to read
without glasses at an age when other people must wear reading glasses.
However, if they have refractive surgery to correct myopia, they may be
able to see distant objects without glasses, but will probably need to
wear glasses to read sometime after age 40, due to presbyopia.
What are signs of myopia?
Nearsighted people may experience headaches or eyestrain and might
squint or feel fatigued when driving or playing sports. Patients who
experience these symptoms while wearing glasses or contact lenses may need
a comprehensive eye examination, as well as a new prescription.
What causes myopia?
Nearsightedness runs in families and usually appears in childhood. This
vision problem may stabilize at a certain point, although sometimes it
worsens with age. This is known as "myopic creep."
What is the treatment for myopia?
Non- surgical treatment options for myopia include glasses and contact
lenses. Surgical treatment options include ALK, clear lens extraction,
LASEK, LASIK, LASEK, phakic IOL and RK. While there are numerous surgical
options available, not all individuals are good candidates for specific
procedures. Patients should review these options in depth with their
physicians prior to making any final decisions.
What is hyperopia (farsightedness)?
 Hyperopia
or farsightedness occurs when light rays are not bent enough to focus on
the retina. Hyperopia is a common vision problem, affecting about
one-fourth of the population. If the eye is too short from front to back,
light rays reach the retina before they converge (focus). People with
hyperopia can sometimes see distant objects very well, but may have
difficulty seeing objects that are close.
Young eyes can sometimes compensate for this refractive error ---
depending on age and the degree of hyperopia present. But with aging, the
human lens loses this ability and a hyperopic person eventually may have
difficulty seeing objects at a distance, as well as those that are nearby.
In fact by age 40, even those with little or no refractive error will
begin to experience difficulty focusing on close objects.
What are signs of hyperopia?
Farsighted people sometimes have headaches or eyestrain, and may squint
or feel fatigued when performing work at close range. Patients who
experience these symptoms while wearing glasses or contact lenses may need
an eye exam and a new prescription.
What causes hyperopia?
Most children are born with hyperopia, but most of them "outgrow"
it as the eyeball lengthens with normal growth. Sometimes people confuse
hyperopia with astigmatism; both cause difficulty in seeing close objects,
but have different causes.
What is the treatment for hyperopia?
Non-surgical treatment options include glasses and contact lenses.
Surgical treatment options include clear lens extraction, CK, LASIK, LTK,
phakic IOL, and PRK. While there are numerous surgical options available,
not all individuals are good candidates for specific procedures. Patients
should review these options in depth with their physicians prior to making
any final decisions.
What is astigmatism?
 Regular
astigmatism occurs when light rays are focused at more than one point on
the retina. Astigmatism is the most common vision problem. It occurs when
the cornea surface is not ideally rounded, but is curved more along one
axis than the other --- that is, when the eye is shaped more like the side
of a football than a basketball. Light entering the eye does not focus
symmetrically on the retina. The result is astigmatism, which blurs both
near and distance vision. This refractive error may occur in patients who
are either myopic (nearsighted) or hyperopic (farsighted). There are
various types of astigmatism included regular, mixed and irregular
astigmatism.
What are the signs of astigmatism?
Patients with only a small amount of astigmatism may not notice it or
may have slightly blurred vision. Sometimes uncorrected astigmatism can
cause headaches or eyestrain and distort or blur vision.
Eyeglasses or contact lens prescriptions with three parts indicate some
amount of astigmatism. A prescription with three parts looks like this:
-2.75 -1.25 x 180. The first part indicates the main spherical correction,
while parts two and three show the extent and location of your
astigmatism.
What is the treatment for astigmatism?
Currently, excimer lasers in the US are approved for treatment of
regular and mixed astigmatism. Recent advances in technology now allow for
the therapeutic treatment of induced irregular astigmatism. In the future,
this application may be expanded to include all types of irregular
astigmatism. Patients who believe they have astigmatism should discuss
this subject in further detail with their physician to gain a better
understanding of the mechanisms in their case.
What is presbyopia (age-related difficulty
with near vision)?
With increasing age, the lens inside of the eyes loses the ability to
focus on nearby objects. The problem usually manifests itself around age
40 and can be corrected with bifocals or reading glasses. This is a normal
aging process, called presbyopia and all people develop.
Some people with myopia can use their natural nearsightedness to read
without glasses at an age when other people must wear reading glasses.
However, if they have refractive surgery to correct myopia, they will be
able to see distant objects without glasses, but probably will need to
wear glasses to read sometime after age 40 due to presbyopia.
What is monovision?
Monovision is a method of distance vision correction to account for
presbyopia. In monovision, refractive surgery is used to adjust one eye for
"near" vision and the other eye for "distance" vision. Contact lenses or
glasses may be required for best distance or night vision activities,
including driving. This option is not suitable for everyone and a trial
period of monovision using contact lenses may help decide if it is right for
the patient.
[back to top]
What is
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. It is caused by a virus which is very contagious and spreads easily.
The virus may affect one or both eyes. At its onset, conjunctivitis is
usually painless and does not adversely affect vision but can be
uncomfortable. The body's defenses will clear viral conjunctivitis in one
to three weeks, and medication is not always necessary. Cold compresses
several times a day on the eyes may offer relief as may artificial tears
and dark sunglasses.
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.
[back to top]
What is a pterygium?
 A pterygium is a triangular-shaped tissue growth, yellow-white to
pinkish in color, on the nasal side of the cornea. It may become red,
inflamed or advance toward the center of the eye. 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 and wind is strong or dust is prevalent, wearing
protective eyeglasses, sunglasses, and/or hats with brims are suggested.
It is a benign condition and will not spread to damage the internal part
of the eye. Because a pterygium is visible, many people want to have it
removed for cosmetic reasons. Lubricants can reduce the redness and
provide relief from the chronic irritation.
[back to top]
What are cataracts?
 "Cataract" is the name used to describe a condition wherein
the lens of the eye becomes opacified or cloudy blocking some light from
reaching the retina and interfering with vision. Cataracts are
multi-faceted. We don't know all the causes, but we do know that time,
aging, and hereditary factors all play a role in cataract development.
Cataract formation can be accelerated by trauma, diabetes, sunlight, and
certain medications. Typically, cataracts occur in adults ("adult
onset"), but may occur as a congenital disorder. More than half of
all Americans age 65 and older have a cataract.
 What
are the symptoms of cataracts?
Early signs of cataracts include blurred or cloudy vision; frequent
changes in eyeglass or contact lens prescriptions; night glare and hazy
vision; and colors that seem to fade. An ophthalmologist must determine if
these symptoms are really caused by a cataract or by some other eye
problem that may need treatment.
 For
an adult, a cataract should be removed only when it interferes with
lifestyle and makes it difficult to continue normally enjoyable
activities. Generally, there is no such thing as a cataract being "ripe"
or "not ripe" for removal. What matters is whether or not the
problem interferes with vision. In rare instances, a "hyper-mature"
cataract may cause elevated eye pressure or inflammation of the eye. In
this case, it must be removed immediately. Otherwise, removal of a
cataract is at the patient's discretion.
What are the different types of
cataracts?
- Age-related cataract: Most cataracts are related to aging.
- Congenital cataract: Some babies are born with cataracts or develop
them in childhood, often in both eyes. These cataracts may not affect
vision. If they do, they may need to be removed.
- Secondary cataract: Cataracts are more likely to develop in people
who have certain other health problems, such as diabetes. Also,
cataracts are sometimes linked to steroid use.
- Traumatic cataract: Cataracts can develop soon after an eye injury,
or years later.
What can one expect during cataract
surgery?
 Cataract surgery is the most frequently performed surgery in the United
States - and the most successful. Over 95 percent of those who have
cataract surgery regain vision levels between 20/40 and 20/20.
Cataract
surgery usually lasts less than one hour and is almost painless. Many
people choose to stay awake during surgery and have an anesthetic to numb
the nerves in and around the eye.
 A lens implant (intraocular lens) inserted during cataract surgery gives
the surgeon an opportunity to correct nearsightedness or farsightedness. Current
research on intraocular lens implants also may provide high quality correction
for astigmatism and for both bifocal and multi-focal vision. Bifocal
implants are currently used, but physicians have yet to achieve
consistently satisfactory outcomes.
The time required for recuperation after cataract removal depends on the
type of procedure performed and the patient's individual rate of healing.
The decision as to which procedure is best for an individual's eye is made
by the patient's ophthalmologist.
One technique ophthalmologists use is phacoemulsification. This
procedure involves making a tiny incision, about 2.5 to 3.5 millimeters in
length. A pencil-like instrument, inserted through the opening, is used to
emulsify (breakdown in to tiny pieces) and aspirate the clouded lens
material. Then the intraocular lens is inserted into place.
Other techniques include:
- Phacofracture cataract surgery - the lens is removed through a small
incision by "fracturing" it into several small segments
- Extracapsular cataract surgery - the lens is removed in one piece
through a larger incision
- Intracapsular surgery - the lens and capsule are completely
removed, a rarely used procedure
In some cases after cataract surgery, a haziness develops in the
membrane or capsule supporting the intraocular lens implant. When this
happens, a laser is sometimes used to create a small opening in the
membrane (a capsulotomy) through which the patient can see clearly. Lasers
are used because they are able to make a small, very precise opening.
Are lasers used during cataract
surgery?
During the past three decades, the techniques and results of cataract
surgery in the U.S. have changed dramatically:
- Ophthalmologists have moved from intracapsular cataract extraction
as the preferred method to almost exclusive use of extracapsular
techniques.
- Smaller incisions have become the standard: Ultrasonic (U/S)
phacoemulsification is now the method of choice for most surgeons.
- Improved surgical techniques for removing the anterior lens capsule
have decreased the incidence of both intraoperative (during surgery) and
postoperative capsular complications.
- Along with these advances have come improved intraocular lens
materials and designs, which are especially well suited for use with
smaller incisions.
- Improved wound construction allows many wounds to be left unsutured.
- Smaller wounds require shorter recovery time and allow greater
intraoperative control and safety.
Despite these advances, however, U/S phacoemulsification techniques are
not without potential sight-threatening complications.
Complications related to U/S phacoemulsification include the possibility
of corneal or scleral burn, iris trauma, rupture of the posterior capsule,
loss of vitreous fluid, cystoid macular edema, and induced astigmatism.
These complications may lead to compromised vision prompting
investigations into newer techniques of using laser energy to remove
cataracts.
The advantages of using a laser to remove cataracts include the ability
to use fiber optics with a smaller diameter than typical ultrasonic
probes; and direct energy precisely on target tissue by means of a smooth,
blunt, stationary probe.
Theoretically, the use of a laser, compared with U/S
phacoemulsification:
- reduces heat and vibration in the wound and in the eye
- decreases the chance of capsular rupture
- requires smaller incisions
- allows faster recovery
Currently, Bascom Palmer Eye Institute is one of several sites
involved in a clinical study to see if laser energy can safely break the
cataract into pieces. This study also will determine if the laser method
of cataract removal, called laser photofragmentation or phacolysis, is as
good as or better than ultrasound phacoemulsification.
[back to top]
What is dry eye?
Among the many different reasons for eye discomfort, by far the most
common is "dry eye." This condition, characterized by unstable
tear film, is distinct from other mechanical dysfunctions (i.e.,
blepharitis and blocked tear ducts) which have comparable symptoms but are
less serious.
Prior to the development of explicit tests, a dry eye diagnosis often
masked additional underlying dysfunctions which resulted in ineffective
treatments. Now, with our ability to diagnose all abnormalities, there is
new and valuable insight into the actual cause and effects of the disease.
For example, it was previously assumed that the irritation suffered by dry
eye patients was due to a lack of tears. Given new information, Bascom
Palmer specialists have disproved this theory. They've shown that eye
comfort depends not on "tears," but on the lubricating "mucous
layer" of tears produced by cells on the conjunctiva of the eye.
Patients with a significant loss of these cells suffer what is described
as Keratoconjunctivitis sicca.
[back to top]
Who are the cornea and
external disease and refractive surgery specialists at Bascom Palmer Eye
Institute?
Eduardo C. Alfonso, M.D.
Richard M. Awdeh, M.D.
William W. Culbertson, M.D.
George F. Corrent, M.D., Ph.D.
Kendall E. Donaldson, M.D., M.S.
Richard K. Forster, M.D.
Anat Galor, M.D.
David A. Goldman, M.D.
Anita Gupta, M.D.
Carol L. Karp, M.D.
Yunhee Lee, M.D., M.P.H.
Terrence P. O'Brien, M.D.
Victor L. Perez, M.D.
Jill Rodila, M.D.
Lana Srur, M.D.
Sonia Yoo, M.D.
Other Cornea and External
Disease and Refractive Error Resources
American
Academy of Ophthalmology
Cornea
Research Foundation of American
Eye Bank
Association of America
Eye
Resources on the Internet
Fuch's Dystrophy
The LASIK
Institute
National
Eye Institute
National
Keratoconus Foundation
Research to
Prevent Blindness
[back to top]
| 