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Acuity
What
is visual acuity?
Visual
acuity is the medical term for sharpness of vision. It deals with the
sharpness, or discrimination, of central vision, rather than the extent or
clarity of peripheral vision. Refractive errors, which can be corrected
with eyeglasses, are the most common cause of poor visual acuity. These
include myopia, or nearsightedness; hyperopia,
or farsightedness; and astigmatism. Myopia is a
reduced ability to see distant objects clearly, hyperopia is a condition
that initially causes difficulty in seeing nearby objects and progresses
to affect distance vision, and astigmatism is blurred vision caused by
abnormal curvature of the front surface of the cornea.
How
is visual acuity measured?
Overall
visual acuity is measured by using the Snellen Eye Chart, with the large E
at the top followed by rows of letters where each row is smaller than the
previous one. A chart using the letter E facing up, down, left, and right
is used for children and those who do not read.
For
the test, the eye chart is placed 20 feet from the person being examined.
For someone wearing eyeglasses, the test first is performed without
glasses. One eye is covered, and the person reads the lowest line on the
chart that can be ascertained. Then the same procedure is followed to test
the other eye. Last, the sequence is performed while the eyeglasses are
worn.
A
reading of 20/20 is normal vision, meaning that the smallest symbol that
can be read at a distance of 20 feet is the same as the symbol that a
person with normal vision would detect at that distance. A 20/40 reading
means that the person can read at a distance of 20 feet what a person with
normal vision reads at 40 feet. A person whose vision can be corrected to
20/200 vision in the better eye is considered legally blind.
Near
visual acuity is measured with the Jaeger card, which has print samples of
different sizes. The card is held 14 inches from the person’s eye for
the test. A result of 14/20 means that the person can read at 14 inches
what someone with normal vision can read at 20 inches. The results of
visual acuity tests are used to prescribe eyeglasses or other corrective
measures.
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Allergies
of the Eye
Allergies
occur when the body overreacts to often-harmless substances in the
environment. Triggered by the body's immune system, allergies protect eyes
from injury. Because the eye is an exposed area of the body, foreign
particles such as pollen, animal dander, and mold spores can adhere to the
moist ocular surface and cause the same types of allergic reactions as
generated when the particles reach the nose, throat, or lungs.
Although
people with eye allergies often have hay fever or other allergic problems,
sometimes the eye reaction can come as a complete surprise. Visible
symptoms of eye allergies may include swelling, hives, itching, watering,
redness, eye pain, and sensitivity to light. Symptoms of eye allergies are
similar to symptoms of infectious diseases of the eyes, so diagnosing and
treating ophthalmic allergic conditions can be a challenge.
What
causes eye allergies?
Allergic
reactions in the eyes, or ocular allergies, can be caused by airborne
particles such as pollen, animal dander, dust, or molds. Eye allergies can
be seasonal, or they may be perennial, affecting sufferers unpredictably
throughout the year. Bacteria, food sensitivities, cosmetics, fabrics,
soaps, and other substances may cause year-round allergies. Plant pollens
and molds are the most common causes for chronic seasonal allergies.
People who wear contact lenses can have ocular allergies to contact lens
solutions as well as to the environment.
Airborne
allergens can readily reach the conjunctiva, which is the thin,
transparent membrane that lines the inner surface of the eyelid and covers
the sclera where it becomes the white of the eye.
How
do you protect your eyes from allergies?
The
best way to protect your eyes from allergies is to avoid allergens
completely. Some of the most common ones are cigarette smoke, cat dander,
smog, some houseplants, and petroleum solvents. It's important to
determine the cause of allergies where possible. An allergist can
administer a comprehensive battery of diagnostic tests.
You
can apply ice packs and cold compresses over your eyes to provide relief
from allergic reactions, thereby reducing puffiness and itching. Using a
tear substitute helps to remove and dilute allergens, and you can use
ointments and time-released tear replacements at night to moisturize the
ocular surface. Applying a topical antihistamine reduces eye redness and
itching. Mild topical steroids, which should only be used under a doctor's
supervision, can treat acute or chronic cases. Eyeglasses and facial hair
can collect allergens, so clean them frequently. A facemask can often
provide relief when you are outside, while special air filters, either
freestanding or furnace-mounted, can minimize the allergens in the air
inside your home.
Many
allergies are seasonal, and the symptoms disappear for periods of time.
However, every time your eye is inflamed, it never completely recovers.
Allergies of the eye should be taken seriously and treated by an eye
doctor to prevent more serious consequences.
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Amblyopia
Amblyopia,
or lazy eye, is poor vision in an eye that failed to develop normal sight
during early childhood. It is usually caused by a lack of use of that eye
because the brain has learned to favor the other eye. To protect a child's
vision, amblyopia should be corrected during infancy or early childhood.
What
types of amblyopia exist?
Any
condition that affects normal use of the eyes and visual development can
cause amblyopia. There are three major causes of amblyopia, and the
condition is sometimes hereditary:
-
Strabismus
is the most common cause of amblyopia and often occurs in eyes that
are not aligned properly or are crossed. The crossed eye turns off to
avoid double vision, and the other eye takes over most of the visual
function. Because the brain favors one eye over the other, the
nonpreferred eye is not adequately stimulated, and the brain cells
responsible for vision in that eye do not mature normally.
-
Refractive
amblyopia is caused when the eyes have unequal refractive power.
For instance, one eye may be nearsighted and the other farsighted.
Amblyopia occurs when the brain cannot balance this difference and
chooses the easier eye to use. The eyes appear normal but, because the
brain is using only one eye most of the time, the other has poor
vision. This type of amblyopia is hard to detect and requires careful
measurement of vision.
-
A
third cause of amblyopia is any eye disease or injury that prevents a
clear image from being focused inside the eye. For example, cataracts,
which occur when the eye's natural lens becomes cloudy, can cause
amblyopia.
How
is amblyopia detected?
Unless
an eye is misaligned, amblyopia is not easily detected, especially in a
child. Children are often not aware that they have one strong eye and one
weak eye because their sight has been that way since birth. And, without
obvious abnormalities, there is no way for parents to tell that a problem
exists with the child's vision. Therefore, you should schedule a
comprehensive vision exam for your child to detect a difference in
refractive power between the two eyes. Children should have their first
exam by the age of 4. If you suspect any vision problems, if your child's
eyes appear misaligned, or if there is a family history of amblyopia, you
should schedule an appointment for your child at a younger age.
How
is amblyopia corrected?
Treating
the cause alone cannot cure amblyopia. Treatment always requires forcing
the brain to use the nonpreferred eye. Eye patching and vision
therapy are the most effective means of treatment. By patching the
normal eye for most or part of the day, often for weeks or months, the
brain must use the weaker eye. To correct errors in focusing or to balance an unequal
refractive power between both eyes, glasses may be prescribed. Vision therapy
then trains the brain to use the eyes to work together.
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Anatomy
of the Eye and How We See

The
eye functions much like a camera with two lenses. The first lens is the cornea,
a clear membrane that covers the front of the eye. The second lens is the eye's
natural crystalline lens, which is located behind the pupil. The cornea is
responsible for about 70 percent of the eye's focusing power, while the natural
lens "fine-tunes" the image before it is focused on the retina at the
back of the eye. If both lenses are
working properly, the image is focused precisely on the surface of the retina
for clear, crisp picture. The retina works like the film in a camera, receiving light
images and sending them through the optic nerve to the brain. The visual cortex
in the back of the brain combines the two image into a single picture for
binocular (two-eyed) vision.
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Astigmatism
Astigmatism
is a vision disorder that occurs when the cornea of the eye is uneven in
shape. More rarely, it can result from the way in which the eye's natural
crystalline lens refracts light. Either condition causes a distorted image
to fall on the retina.
The
human eye works much like a camera with two lenses -- the cornea,
which is a clear membrane that covers the front of the eye, and the
natural crystalline lens, which is located behind the pupil. These two
lenses work together to focus light on the retina, which is the membrane
that covers the back two-thirds of the eye and works like the film in a
camera. A normal cornea should be curved equally in all directions,
allowing light to focus exactly on the surface of the retina.
Most vision problems result from an irregularity in the curvature of the
cornea or in the shape of the eye.
What
causes astigmatism?
If
the cornea is uneven in shape, the result is astigmatism, which causes
light rays to be bent out of focus, either horizontally or vertically,
resulting in distorted vision at all distances.
Astigmatism
is prevalent and, in most cases, if you have it, you were born with it.
Just as your hands are shaped differently from other people's hands, so
are your eyes. Eyelid swelling, corneal scars, and keratoconus,
a rare condition that causes the cornea to be misshapen, can also cause
astigmatism.
How
do you know you have astigmatism?
Very
mild astigmatism may cause no visual symptoms because the muscles of the
eye will compensate for the uneven curvature of the cornea. If the eye has
to work too hard to compensate, however, eyestrain and headaches can
result. In addition, mild astigmatism can cause eye fatigue or blurry
vision at certain distances. Severe astigmatism will usually cause
distorted, double, or blurry vision.
An
eye doctor detects astigmatism during the course of a regular eye
examination.
How
is astigmatism treated?
Astigmatism
can be treated surgically or nonsurgically. Prescription eyeglasses
and contact lenses or laser vision correction surgery correct most cases
of astigmatism. The most prevalent nonsurgical correction is a
prescription for rigid gas permeable
(RGP) contact
lenses. Because it is rigid, an RGP lens will fill in the irregular
areas of the cornea with tears, creating a smooth spherical surface and
correcting astigmatism. Special soft contact lenses called torics
also compensate for the astigmatic shape of the corneas. In those cases
where the astigmatism arises from the eye's natural crystalline lens
rather than the cornea, a special bitoric
contact lens may be prescribed. It offers refracting surfaces on the front
and back to correct the problem in much the same way that eyeglasses do.
If
you are contact lens-intolerant or just want to be free from glasses or
contacts, you may opt to have some form of vision correction procedure
performed by a qualified eye surgeon. LASIK,
the most popular form of laser vision correction, can provide correction
for relatively high degrees of nearsightedness and astigmatism as well as
some cases of farsightedness and astigmatism.
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Blepharitis
Blepharitis
is an inflammation of the eyelids that can affect persons of all ages.
Excess oil is produced in the glands near the eyelid, which creates a
favorable environment for the growth of bacteria. It is a common condition
that has multiple causes. The three most prevalent forms of this condition
are seborrheic, staphyloccocal, and mixed. Another less common, but severe
form of blepharitis, is ulcerative blepharitis.
Seborrheic
blepharitis, the least
severe and most common form, is often associated with dandruff of the
scalp or acne-like skin conditions. It is a dysfunction of a type of gland
that exists in the eyelid and the skin. This type of blephartis usually
affects the mature population and appears as greasy flakes or scales
around the base of the eyelashes and as a mild redness of the eyelid.
Symptoms are itchiness, foreign body sensation, discharge, and burning.
Staphylococcal
blepharitis is an
infection of the eyelids and commonly begins in childhood, continuing
throughout adulthood. Invading bacteria cause inflammation of the eyelids
and produce irritants and bacteria toxins that are harmful to the eye.
Crusting, scaling, hair losses, chronic redness, and whitening of lashes
are common symptoms. Treatment is most important to prevent potential
scarring of the cornea
and conjunctiva.
Mixed
blepharitis is a
combination of both seborrhea and staphyloccocal forms of this condition,
and symptoms of both types can appear.
Ulcerative
blepharitis is
characterized by matted, hard crusts around the eyelashes that result in
small sores that may bleed or ooze when removed. Loss of eyelashes,
distortion of the front edges of the eyelids, and chronic tearing may also
occur. The cornea may also become inflamed.
In
any form of blepharitis, the conjunctiva and cornea can be affected. Even
mild conditions can be uncomfortable and unattractive, and if untreated,
can lead to more serious problems. Complications - such as prolonged
infection, injury to the eye tissue from irritation (corneal ulcer),
inflammation of the conjunctiva, loss of eyelashes, and scarring of the
eyelids - may occur.
How
is blepharitis controlled?
Good
eyelid hygiene is essential in treating blepharitis. Warm, moist
compresses can also help relieve symptoms when used in conjunction with
regular eyelid cleansing. Because staphylococcal blepharitis is an
infection, antibiotics and/or corticosteroids can treat the infection and
help reduce the swelling.
Although
chronic and bothersome, blepharitis can be controlled. Symptoms, however,
are chronic, recurring, and remitting, and there may be no definitive
cure. The problem can disappear for long periods of time and then return.
Medication alone is not sufficient treatment, and keeping the eyelids
clean is essential to restoring a normal, healthy environment.
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Cataract
What is a
cataract?
The lens of the
eye, the part that helps focus light onto the retina which in turn sends
the visual signals to the brain (see Anatomy
of the Eye), is made mostly of water and protein. When too much
protein builds up, it clouds the lens blocking some of the light and
impairing vision. That protein build-up is the formation of a cataract. It
is not a growth, but rather a clouding or hazing of the lens.
How many people
get cataracts?
A significant
number of people ages 65 or older have some degree of cataract. In fact,
developing cataracts is a normal part of aging. That does not mean,
however, that every senior will need treatment for cataract problems.
What causes
cataracts?
The cause of
cataracts is generally unknown. Most often, cataracts occur as a person
ages, called age-related cataracts or more scientifically, nuclear
sclerotic cataracts. Cataracts can also result from a variety of
environmental conditions and injuries and are called either secondary
or traumatic cataracts. Some babies are born with cataracts, called
congenital cataracts. Generally, potential risk factors for
developing cataracts include but are not limited to:
-
65 years of
age or more
-
Family
history of cataracts
-
Smoker or
former smoker
-
Grossly
over- or underweight
-
Diabetes
-
Have taken
steroids or certain other medications
-
Suffered a
blunt or penetrating eye injury
-
Excessive,
long exposure to UV light
What are the
symptoms of cataracts?
Some people
compare cataracts to looking through a frosted piece of glass, fog, or
film covering their sight. Many don’t even know they have cataracts if
the cloudiness has not greatly altered their eyesight. Others with
cataracts, however, have lost their ability to perform routine activities.
Glare may also be a problem, and many people with cataracts complain of
halos around lights.
Additional
symptoms include colors that seem faded, a temporary symptom called
"second sight" which occurs when people can read again close up
without glasses even though they have not done this for years, decreased
night vision, and frequent changes in eyeglass or contact lens
prescription.
It is important
to note, however, that although these symptoms can indicate the formation
of cataracts, they can also signal other vision problems. Cataracts
develop and grow slowly and cause more pronounced symptoms as they
"mature." Patients experiencing any of these symptoms are
advised to consult their eye care professional for a thorough evaluation.
What is the
treatment for cataracts?
The first step
in treating cataracts is detection. To determine whether or not a person
has cataracts, an eye care professional conducts a comprehensive eye exam,
which includes a visual acuity
test, pupil dilation, and a tonometry
test to measure the pressure inside the eye. The early stages of cataracts
can sometimes be treated with eyeglasses, alternative lenses or a simple
change in environmental lighting. For more advanced cataracts that have
caused a loss of routine activities or other problems, surgery is the only
effective treatment option.
Surgery:
Cataract removal is one of the most popular surgeries performed in the
United States today. It is safe and highly effective in improving vision.
The most common procedure is called extracapsular cataract extraction
(ECCE) or phacoemulsification (phaco). In phaco, after making a ¼-inch
incision, the surgeon uses sound waves or ultrasonic vibrations to break
up the cloudy lens so it can be removed by suction through a tiny hollow
tube.
In some
instances, eye care professionals may choose an older method of cataract
removal in which the entire lens is removed through a ½-inch surgical
incision. After a lens is removed, it must be replaced. The most common
lens replacement is called the intraocular lens (IOL). An IOL is a clear
plastic lens implant that is placed inside the eye permanently, thus
requiring no care. Patients do not feel or see the new lens.
When an
intraocular lens implant is not the best solution, the doctor may
prescribe contact lenses or, in rare cases, corrective eyeglasses as lens
replacement.
What is
involved in cataract surgery?
Prior to
surgery, an eye care professional will conduct a comprehensive eye exam or
cataract exam to determine eye health and to use as a guide during the
surgery.
The patient is
given eye drops to enlarge the pupil of the eye to be operated on, giving
the surgeon better access to the lens. Some people choose to remain awake
during the procedure and select local anesthesia, which may be
administered as eye drops, injections close to the eye, or both. Others
require general anesthesia to keep them relaxed throughout the procedure.
Depending on the
type used, anesthesia may be given about half an hour before surgery in a
pre-operation (pre-op) room or immediately before surgery at the operating
table. The anesthesia prevents any pain and helps keep the eye from
moving.
When ready, the
patient lies back on a table and the eye is gently washed. Then a sheet is
placed over the patient’s face with an opening for the surgeon to access
the eye. Often, a member of the eye care team (surgeon, nurses, and
assistants) provides additional air for increased comfort.
The surgeon
generally sits behind the patient and uses a surgical microscope unit that
can be swung over the table, to obtain a clear, enhanced image of the eye.
Lighting is dimmed. With extracapsular or phaco surgery, an incision less
than ¼ inch in measurement is made and the surgeon uses the phaco
ultrasonic instrument to break up the cloudy lens, then removes the pieces
using suction through a tiny hallow tube. Though the cloudy lens is
removed, the surgeon leaves intact the lens capsule or outer covering and
inserts an intraocular lens (IOL) through the incision to replace the
cloudy lens. The incision heals on its own without stitches. Anesthesia
helps prevent any pain or discomfort. Overall, the entire surgical
procedure usually takes less than 30 minutes. Sometimes a protective
covering is placed over the eye when surgery is completed.
What happens
after surgery
Recovery time is
scheduled immediately following surgery to allow recuperation from the
procedure and anesthesia. Patients generally go home afterward, with the
help of another driver because vision may still be impaired.
For a day or two
following surgery, patients may experience mild discomfort such as itching
or stickiness when blinking. These symptoms usually disappear within 1 to
2 days.
Usually patients
return to their surgeon the day after the procedure for their first follow
up examination. Surgeons often prescribe eye drops to help minimize the
mild inflammation that occurs in the eye after surgery.
The healing
process may take weeks, but many patients begin to resume visual
activities, such as reading and watching television, shortly after
surgery, even with some blurred vision.
What are the
risks of surgery and what follow up is needed?
As with any
surgery, there are some risks involved in cataract surgery. A rise in the
eye’s pressure is why it is essential for patients to follow a strict
post-surgery check-up schedule. Because an incision is made in the eye,
infection is also a risk, though managed easily with oral or eye-drop
antibiotics. Other risks are hemorrhage or retinal detachment. It is
important to point out that cataract surgery is common and risks are
considered minimal. Patients are advised to discuss all the risks in
detail with their eye care professional.
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Color
Blindness
What
is color blindness?
Color
blindness is a condition in which a person has trouble telling the
difference between various shades of color. Color blindness does not mean
that a person sees things in black and white. Generally, optometrists and
doctors refer to the condition as 'color vision deficiency.'
Who is affected by color vision deficiency?
Almost
all color vision problems are inherited, and present at birth. It is
estimated that 1 in every 12 males, and one in every 200 females, are born
with some form of color vision deficiency.
In
later life, some serious eye diseases, and certain medications can cause color
vision deficiencies to appear.
How
is a color vision deficiency inherited?
The
'color blindness gene' is passed down through the mother's side of the
family.
A
color blind male will have inherited the condition through his mother's
genes (although she will probably not be color blind).
A
color blind female will have inherited the condition through a combination
of her mother's genes (probably not color blind) and her father's genes (color
blind).
Who should be tested for color vision deficiency?
People
who should have there color vision checked
-
All
Boys
-
Girls
in whom color vision is suspect
-
Children
with a family history of color blindness (particularly from uncles
or grandfather)
-
Adults
considering occupations that require fine color discrimination
-
Adults
considering occupations that have color vision standards
-
Adults
who have developed eye disease, such as cataract or macula
degeneration
Color vision testing is fairly simple, and can be carried out with little
difficulty from the age of 3 years (the child doesn't have to know the
names of the colors).
What
can be done about color blindness?
Medically,
there is no cure for hereditary colorblindness, because the body lacks a
given sensor for detecting particular colors.
Color
blind
people often look for other cues to determine color. For example, if you
couldn't tell the difference between the red and the green at a traffic
light, you could still tell that the top light meant stop!
Other
means of compensating for color blindness have been developed, such as
specially tinted glasses. There are even computer programs available to
help color blind people distinguish colors.
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Conjunctivitis
More
commonly known as "pink eye", conjunctivitis is an eye infection
that can be highly contagious. It causes the conjunctiva, the thin
transparent layer covering the inner eyelid and the white part of the eye,
to become inflamed, irritated and red.
What
causes conjunctivitis?
Conjunctivitis
occurs most commonly in children, though it can occur at any age. There
are generally four types of conjunctivitis:
-
viral
-- which accompanies a cold or other viral infection
-
bacterial
-- such as from strep, staph or other bacterial infections
-
allergic
-- an allergy to dust, molds, pets, cosmetics and other potential
irritants
-
ophthalmia
neonatorum -- a form of conjunctivitis found only in newborns
Other
possible causes of conjunctivitis include a partially blocked tear duct,
unsanitary environments, and working with intense light.
Symptoms
of conjunctivitis may be nothing more than a minor irritant to some
people. Others, however, may notice several other, more painful, symptoms
including itching, swelling, crusty eyelids after sleeping, a discharge
from the eye, excessive watering, light sensitivity, and excessive
redness.
How
is it treated?
Most
often, conjunctivitis disappears on its own with self-care and typically
improves within one week. Because conjunctivitis spreads easily from eye
to eye and person to person, it is important to exercise good hygiene
during an episode of conjunctivitis. People with conjunctivitis should
wash their hands frequently, avoid touching their eyes, refrain from
wearing makeup, and not share towels, linens or other items in contact
with the infected eye. To ease discomfort, warm-water compresses may be
used, taking care to discard or launder the compress after use.
If
symptoms do not resolve and the eye is left untreated, conjunctivitis can
damage the cornea and affect vision permanently. Seek immediate medical
attention if the conjunctivitis does not disappear or the following more
severe symptoms occur:
Usually,
eye care professionals can test the discharge with a simple culture and
establish the exact cause of conjunctivitis. In some cases, doctors may
prescribe antiviral, antibiotic eye drops or ointments to control the
infection. In cases of allergic conjunctivitis, removing the source of
allergy may solve the problem, or antihistamine eye drops or steroid-based
medications may be prescribed if removal of the allergen is not possible.
Newborns are routinely treated with antibiotic eye drops or ointment.
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Cornea
The
tough, clear membrane that covers the front of the eye and protects the
inner parts of the eye is called the cornea. (See diagram under
"Anatomy of the Eye.") It serves as the outer
lens of the eye and provides approximately 70 percent to 80 percent of the
eye's refractive power. Fine-tuning is provided by the natural crystalline
lens that lies behind the pupil. Together these two lenses focus light on
the retina at the back of the eye, which sends electrical signals to the
brain enabling a person to see. The shape of the cornea and its general
condition determine, to a large degree, the visual powers of the eye.
Although
the cornea contains the highest concentration of nerve fibers of any
structure in the human body, it contains no blood vessels. That is one
reason why the cornea remains clear. The cornea receives nutrition from
the fluid interior of the eye and from the outer tear film surface.
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A
corneal ulcer forms when the surface of the cornea is damaged. Ulcers may
be sterile (no infecting organisms) or infectious. Whether or not an
ulcer is infectious is an important distinction for the physician to make
and determines the course of treatment. Bacterial ulcers tend to be
extremely painful and are typically associated with a break in the
epithelium, the superficial layer of the cornea. Certain types of
bacteria, such as Pseudomonas, are extremely aggressive and can cause
severe damage and even blindness within 24-48 hours if left untreated. Sterile
infiltrates on the other hand, cause little if any pain. They are
often found near the peripheral edge of the cornea and are not necessarily
accompanied by a break in the epithelial layer of the cornea.
There
are many causes of corneal ulcers. Contact lens wearers (especially
soft) have an increased risk of ulcers if they do not adhere to strict
regimens for the cleaning, handling, and disinfection of their lenses and
cases. Soft contact lenses are designed to have very high water
content and can easily absorb bacteria and infecting organisms if not
cared for properly. Pseudomonas is a common cause of corneal ulcer
seen in those who wear contacts.
Bacterial
ulcers may be associated with diseases that compromise the corneal
surface, creating a window of opportunity for organisms to infect the
cornea. Patients with severely dry eyes, difficulty blinking, or are
unable to care for themselves, are also at risk. Other causes of
ulcers include: herpes simplex viral infections, inflammatory
diseases, corneal abrasions or injuries, and other systemic diseases.
The
symptoms associated with corneal ulcers depend on whether they are
infectious or sterile, as well as the aggressiveness of the infecting
organism.
·
Red eye
·
Severe pain (not in all cases)
·
Tearing
·
Discharge
·
White spot on the cornea, that depending on the severity of
the ulcer, may not be visible with the naked eye
·
Light sensitivity
Corneal
ulcers are diagnosed with a careful examination using a slit lamp
microscope. Special types of eye drops containing dye such as
fluorescein may be instilled to highlight the ulcer, making it easier to
detect. If an infectious organism is suspected, the doctor may
order a culture. After numbing the eye with topical eye drops, cells
are gently scraped from the corneal surface and tested to determine the
infecting organism.
The
course of treatment depends on whether the ulcer is sterile or infectious.
Bacterial ulcers require aggressive treatment. In some cases,
antibacterial eye drops are used every 15 minutes. Steroid
medications are avoided in cases of infectious ulcers. Some patients
with severe ulcers may require hospitalization for IV antibiotics and
around-the-clock therapy. Sterile ulcers are typically treated by
reducing the eye's inflammatory response with steroid drops,
anti-inflammatory drops, and antibiotics.
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Dry
Eye
Dry
eye is a term used to describe a condition in which the eyes either
produce too few tears or they tear without the proper chemical
composition. There may be as many as 34 million Americans who experience
some of the symptoms of dry eye. The condition is most often the result of
the natural aging process. However, it may also be caused by:
-
Problems
with the blinking reflex
-
The
use of certain types of medications
-
Environmental
factors such as a dry climate or exposure to wind
-
Chemical
or thermal burns to the eye
-
Some
health problems, such as arthritis or Sjogren's syndrome.
One
of the symptoms of dry eye is excessive watering of the affected eye. The
watering is a natural reflex, caused by irritation of the surface of the
eye because the tears are of abnormal chemical composition. This symptom
is one of the primary reasons why so many people with the disorder do not
consider the possibility that the term "dry eye" might apply to
them. Other symptoms are an eye that is scratchy, dry, irritated or
generally uncomfortable. Sometimes redness, a burning sensation, or the
feeling of having something in your eye may also occur.
Because
these symptoms can occur in conjunction with many disorders, the only way
to be sure about a condition with such symptoms is to visit an eye
doctor.
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Esotropia,
or "crossed" eye
Esotropia
is the most common form of strabismus in infants, a condition that refers to any
misalignment of the eyes. In the case of esotropia, one eye deviates inward
toward the nose while the other fixates normally. (Exotropia is the condition
where one eye deviates outward, away from the nose.) Strabismus, also
called "cross-eye," occurs in about four percent of all children in
the United States. It happens equally in males and females and is sometimes
hereditary. Esotropia can also affect teenagers and adults, and it is usually
related to systemic conditions such as high blood pressure, diabetes, strokes,
or brain injuries.
The
brain's ability to see three-dimensional objects depends on proper alignment of
the eyes. When both eyes are properly aligned and aimed at the same target, the
visual portion of the brain fuses the forms into a single image. When one eye
turns inward, outward, upward, or downward, two different pictures are sent to
the brain. This causes loss of depth perception and binocular vision, or use of
the two eyes together.
Types
of Esotopia
-
Pseudoesotropia
(false esotropia) is actually the physical appearance of cross-eye when the
eyes are perfectly aligned. Infants and young children often have a wide,
flat nose with a fold of skin at the inner eyelid that makes the eyes appear
crossed. This appearance usually disappears as the child grows.
-
Congenital
or infant esotropia
can be present at birth or may develop anytime
during the first 6 months of life. Although it is common for an infant's
eyes to be intermittently misaligned, if the condition persists beyond the
first few months, it should be checked by a physician. One to 2 percent of
children have congenital esotropia, and the condition usually does not
improve with age. Surgical correction is usually recommended between 6 and
14 months of age.
-
Accommodative
esotropia
is a common form that occurs in farsighted
children, usually 2 years old or older. Young children can often overcome
farsightedness by focusing their eyes to adjust to the condition, but the
effort required for this focusing causes the eyes to cross. Eyeglasses can
reduce the focusing effort and sometimes straighten the eyes. In addition,
special eyedrops, ointments, and lenses called prisms may also be effective.
Eye exercises can also be helpful, especially in older children. Sometimes bifocals
can correct the excessive turning in of the eyes for close work.
-
Acquired
esotropia occurs after infancy. Children who have been farsighted
and have not had glasses, or children who were responsive to glasses but
later developed an additional eye-crossing, are the most commonly affected.
Children with acquired eye-crossing require prompt evaluation and treatment
to correct the deviation and to restore binocular vision.
The
causes of some forms of esotropia are not fully understood. There are six
muscles that control eye movement, four that move it up and down and two that
move it side to side. All these muscles must be coordinated and working properly
in order for the brain to see a single image. When one or more of these muscles
doesn't work properly, some form of strabismus may occur. Strabismus is more
common in children with disorders that affect the brain such as cerebral palsy,
Down syndrome, hydrocephalus, and brain tumors.
What
are the symptoms of esotropia?
Symptoms
of esotropia are decreased vision, double vision, and misaligned eyes. Children
with esotropia do not use their eyes together and often squint in bright
sunlight or tilt their heads in a specific direction to use their eyes together.
They may also rub their eyes frequently. Children rarely tell you they are
experiencing double vision, although they may close one eye to compensate for
the problem. You may also notice signs of faulty depth perception.
When
a young child has strabismus, the child's brain may learn to ignore the
misaligned eye's image and see only the image from the best-seeing eye. This is
called amblyopia,
or lazy eye, and results in a loss of depth perception. In adults who develop
strabismus, double vision sometimes occurs because the brain has already been
trained to receive images from both eyes and cannot ignore the image from the
turned eye.
What
are the cures for esotropia?
Treatment
depends on the type of esotropia. Generally, however, treatment can include
correcting a refractive error with glasses, patching to force the use of the
less-preferred eye, and vision therapy to train the
eyes to work together. Sometimes surgery is required.
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Exotropia,
or "wandering" eye
Exotropia
is one of the most common forms of strabismus, a
condition that refers to any misalignment of the eyes. In the case of
exotropia, one eye deviates outward (away from the nose) while the other
fixates normally. Esotropia is the condition
where one eye deviates inward (toward the nose). Esotropia is the most
common type of strabismus in infants, while exotropia often begins between
the ages of 2 and 4. About 4 percent of all children in the United States
have some form of strabismus. It occurs equally in males and females and
is sometimes hereditary. The condition can also develop later in life.
The
brain's ability to see three-dimensional objects depends on proper
alignment of the eyes. When both eyes are properly aligned and aimed at
the same target, the visual portion of the brain fuses the forms into a
single image. When one eye turns inward, outward, upward, or downward, two
different pictures are sent to the brain. This causes loss of depth
perception and binocularity, or normal two-eyed vision.
How
does exotropia occur?
The
causes of exotropia are not fully understood. There are six muscles that
control eye movement, four that move it up and down and two that move it
side to side. All these muscles must be coordinated and working properly
in order for the brain to see a single image. When one or more of these
muscles doesn't work properly, some form of strabismus may occur.
Strabismus is more common in children with disorders that affect the brain
such as cerebral palsy, Down syndrome, hydrocephalus, and brain tumors.
What
are the signs of exotropia?
The
earliest sign of exotropia is usually a noticeable outward deviation of
the eye. This symptom may at first be intermittent, occurring when a child
is daydreaming, not feeling well, or tired. The deviation may also be more
noticeable when the child looks at something in the distance. Squinting or
frequent rubbing of the eyes is also common with exotropia. Your child
probably will not mention seeing double, i.e., double vision. However, he
or she may close one eye to compensate for the problem.
Generally,
exotropia progresses in frequency and duration. As the disorder
progresses, the eyes will start to turn out when looking at close objects
as well as those in the distance. If left untreated, the eye may turn out
continually, causing a loss of binocular vision.
In
young children with any form of strabismus, the brain may learn to ignore
the misaligned eye's image and see only the image from the best-seeing
eye. This is called amblyopia, or lazy eye, and
results in a loss of depth perception. In adults who develop strabismus,
double vision sometimes occurs because the brain has already been trained
to receive images from both eyes and cannot ignore the image from the
turned eye.
How
is exotropia treated?
A
comprehensive eye examination including an ocular motility (eye movement)
evaluation and an evaluation of the internal ocular structures will allow
an eye doctor to accurately diagnose the exotropia. Exotropia responds
very well to vision therapy to train the eyes to work together. Eye
patching is usually required and prisms are occasionally used. In
some children, surgery is required.
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Farsightedness,
or Hyperopia
Farsightedness
is an inherited condition that occurs when the cornea is too flat or the
distance from the cornea to the retina is too short. When this happens, the
light rays coming from an object strike the retina before coming to sharp focus,
or the image is theoretically focused at an imaginary point behind the retina.
The result is a blurred image when trying to focus on something that is up
close, but distance vision remains sharp.
 
Children
who are farsighted can sometimes compensate without corrective lenses because of
the strength and agility of their natural lenses. With a high degree of
hyperopia, however, they may exhibit nonvisual symptoms such as headaches and
lack of interest in reading. As the eye gets older, it loses some of its ability
to accommodate (focus), and eventually, most farsighted individuals need
corrective lenses.
How
is farsightedness corrected?
The
usual treatment for hyperopia is prescription eyeglasses with convex lenses that
curve outward, or contact lenses that counteract the distortion created by
corneas that are too flat in shape. A convex lens moves the image of a distant
object forward onto the retina, thereby bringing it into proper focus.
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Floaters
Floaters
are small grayish or transparent spots or blobs that float across the
field of vision from time to time. Floaters move around with eye
movements, and are most commonly noticed against plain backgrounds, such
as a white page or a blank wall. Floaters can also appear as fine threads,
webs, and clumps. Floaters are
caused by small specks or clumps that form within the fluid of the eye.
When light enters the eye, these clumps cast a shadow onto the retina. The
floater that you notice is the shadow that is cast onto the retina.
Floaters are an annoying phenomenon
that get in the way. Mostly they are harmless. In a small number of cases,
floaters can be a sign of more serious damage that is taking place.
Floaters can occur in anyone, at any time.
What
should I do if I think I might have floaters?
You
should arrange for an eye examination with your local optometrist to rule
out more serious underlying problems. You should seek immediate attention
if you notice any of the following symptoms:
-
An
increase in the number of floaters noticed
-
Decrease
in vision in one or both eyes
-
Flashes
or sparkles in vision
Your
optometrist will advise you if you have floaters, and whether or not they
are potentially dangerous to your vision. Generally, floaters are
annoying. But no treatment is required (provided there are no underlying
problems).
Glaucoma
is a very evasive and dangerous eye disease. It can happen to people
without their knowledge and can cause partial, sometimes, total blindness.
In fact, glaucoma is the second leading cause of blindness in the United
States.
In
simple terms, glaucoma is caused by the excessive buildup of fluid inside
the eye. Eyes are essentially hollow globes filled with a constantly
circulating clear fluid that must drain out of the eye as more is pumped
in. Each eye produces about 4 c.c. of fluid a day, a considerable amount
for an object that is only about 1 inch in diameter.
Sometimes
the eye’s drainage system becomes clogged, causing pressure in the eye
to build up to damaging levels. Unless controlled, damage to the optic
nerve and loss of vision can occur. The earliest sign of optic nerve
damage is often a loss of peripheral (side) vision. However, the early
onset of glaucoma can be detected not by any symptoms but by a
comprehensive eye exam and specific glaucoma tests.
How
many are affected by glaucoma?
The
most common form of glaucoma is called open-angle glaucoma. It is so named
because the angle from which the fluid drains out of the anterior chamber
is open. This form of glaucoma affects approximately 3 million Americans.
Glaucoma occurs in nearly 1 to 2 percent of people over the age of 40.
What
causes glaucoma?
There
is no single cause of glaucoma. Anyone can develop glaucoma, but
generally, those at higher risk than the average population are:
-
People
more than 60 years of age
-
African
Americans over the age of 40
-
People
with a family history of glaucoma
What
are the symptoms of glaucoma?
Only
an eye care professional can determine whether or not a person has
glaucoma and how severe it is. Glaucoma begins without showing any
symptoms. If it remains untreated and undetected, a person may notice a
loss of peripheral vision and the start of tunnel vision. Gradually, sight
diminishes completely. A few glaucoma sufferers have such early symptoms
as severe eye pain, blurred vision, seeing halos around lights, and
constantly dilated pupils, though these are the exceptions.
Note
that experiencing these symptoms does not necessarily signal glaucoma.
Patients with any changes in their vision or optical comfort should see an
eye care professional for a thorough evaluation.
How
is glaucoma detected?
Detection
is vital. For patients, understanding glaucoma helps in both treatment and
long-term eye care. Pressure is key. Glaucoma can occur in eyes with
"normal" pressure readings, though "normal" pressure
varies from person to person. The pressure’s effect on, or the potential
risk to, the optic nerve determines the severity of glaucoma.
To
determine whether a person has glaucoma, an eye care professional conducts
several tests. A tonometry test measures the amount of pressure on the
optic nerve and is usually part of every complete eye exam.
A
popular tonometry test is often referred to as the "air-puff"
test. The patient looks through a machine as it blows a puff of air at the
eye.
Another
form of tonometry, and one of the most accurate, uses a contact tonometer,
an instrument that looks like a pen. After numbing eye drops are
administered, the tip of the tonometer touches the eye and measures the
pressure.
As
a general guideline, pressure above 21 millimeters is considered to be
elevated, though not all persons with that reading will have glaucoma. Eye
care professionals will carefully monitor pressures for early signs of
glaucoma.
Another
test used in detection is an examination of the optic nerve, looking at
the interior of the eye to detect any damage. A pupil dilation test
provides the eye care professional to get a better look at the inner eye.
A visual acuity test helps to evaluate peripheral vision.
What
are the treatments for glaucoma?
-
Medication:
The
first line of treatment is often the use of eye drops administered
three times per day or oral medication to help drain the fluid and
lower pressure. Sometimes eye drops or pills are enough to lower
pressure. As with all medications, it is important to give the eye
care professional a complete history of current medications, allergies
or any other side effects experienced from the medication. Following
the eye drops and oral medication directions closely is equally
important.
-
Laser
Surgery:
When
pressure cannot be lowered adequately or side effects are too severe,
eye care professionals turn to laser treatment as the next, and
necessary, treatment. Laser surgery uses focused light to reopen the
drainage area to alleviate the buildup of fluid. After receiving a
numbing agent in the eyes, patients sit facing the laser machine,
while the eye care professional gently holds a lens used to aim the
laser beam to the eye. A beam of light hits the eye’s lens and
reflects into the drainage area of the eye. The entire procedure
usually takes only minutes.
Generally,
there are no restrictions following laser surgery, but patients are
given eye medications to use for a few days after the procedure. Eye
care professionals will continue to monitor pressure closely and
regularly. Some consider laser surgery a temporary method to reducing
pressure. Studies indicate that the effects of laser surgery diminish
over time. More than half of all patients undergoing laser surgery
show pressure increases in just two years after surgery.
-
Conventional
surgery: Conventional
surgery for glaucoma involves making an incision in the eye to create
a new drainage path. The eye tissue creates a new area for fluid to
drain naturally. Patients cannot feel this draining. The procedure
takes about 10 to 15 minutes. Eye medication is used to prevent
infection. This surgery typically requires close follow-up and a lot
of care afterward. Studies on the effect of surgery indicate that 80
percent to 90 percent of patients have lowered pressure readings after
the surgery. However, there is no cure for glaucoma. Surgery may save
remaining vision but it can not improve sight that has already been
impaired or lost.
What
are the forms of glaucoma?
There
are many types of glaucoma. Open-angle glaucoma is the most common.
All are similar because they relate to an increase or a buildup of
pressure inside the eye.
Angle-closure
or closed-angle glaucoma is characterized by intense pain, starting
with a headache and including such other symptoms as nausea, red eye,
and blurred vision. Angle-closure glaucoma can occur all at once and
be severe, or gradually in small episodes. Both of these types require
immediate medical attention.
Secondary
glaucoma occurs as a result of some other medical problem with the
eye, such as inflammation, injury, advanced cataracts, or certain
tumors. Congenital glaucoma occurs in children born with malformations
in the angle of the eye. Usually, parents detect symptoms, such as
eyes that appear cloudy, severe sensitivity to light, and excessive
tearing or watery eyes. Many eye care professionals recommend surgery
over eye drops, because of the difficulty of administering drops in
infants and the unknown effects of the drops on young eyes. Surgery on
children usually results in adequate vision.
Because
of the many unknown factors surrounding glaucoma, research is focusing
on ways to service patients with the disease. Patients with questions
or concerns regarding glaucoma should contact their eye care
professional or a professional organization dedicated to glaucoma
research.
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Herpes
Simplex Eye Disease
Herpes
simplex is a very common virus affecting the skin, mucous membranes,
nervous system, and the eye. There are two types of herpes simplex.
Type I causes cold sores or fever blisters and may involve the eye.
Type II is sexually transmitted and rarely causes ocular problems.
Nearly
everyone is exposed to the virus during childhood. Herpes simplex is
transmitted through bodily fluids, and children are often infected by the
saliva of an adult. The initial infection is usually mild, causing
only a sore throat or mouth. After exposure, herpes simplex usually
lies dormant in the nerve that supplies the eye and skin.
Later
on, the virus may be reactivated by stress, heat, running a fever,
sunlight, hormonal changes, trauma, or certain medications. It is
more likely to recur in people who have diseases that suppress their
immune system. In some cases, the recurrence is triggered repeatedly
and becomes a chronic problem.
When
the eye is involved, herpes simplex typically affects the eyelids,
conjunctiva, and cornea. Keratitis (swelling caused by the
infection), a problem affecting the cornea, is often the first ocular sign
of the disease. In some cases, the infection extends to the middle
layers of the cornea, increasing the possibility of permanent scarring.
Some patients develop uveitis, an inflammatory condition that affects
other eye tissues.
Signs and Symptoms
·
Pain
·
Red eye
·
Tearing
·
Light sensitivity
·
Irritation, scratchiness
·
Decreased vision (dependent on the location and extent of
the infection)
Herpes
simplex is diagnosed with a slit lamp examination. Tinted eye drops
that highlight the affected areas of the cornea may be instilled to help
the doctor evaluate the extent of the infection. Treatment of
herpes simplex keratitis depends on the severity. An initial
outbreak is typically treated with topical and sometimes oral anti-viral
medication. The doctor may gently scrape the affected area of the
cornea to remove the diseased cells. Patients who experience
permanent corneal scarring as a result of severe and recurrent infections
may require a corneal transplant to restore their vision.
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Keratoconus
Keratoconus
is a degenerative disease of the cornea that causes it to gradually thin
and bulge into a cone-like shape. This shape prevents light from
focusing precisely on the macula. As the disease progresses, the
cone becomes more pronounced, causing vision to become blurred and
distorted. Because of the cornea's irregular shape, patients with
keratoconus are usually very nearsighted and have a high degree of
astigmatism that is not correctable with glasses.
Keratoconus
is sometimes an inherited problem that usually occurs in both eyes.
Signs
and Symptoms
·
Nearsightedness
·
Astigmatism
·
Blurred vision - even when wearing glasses and contact
lenses
·
Glare at night
·
Light sensitivity
·
Frequent prescription changes in glasses and contact lenses
·
Eye rubbing
Keratoconus
is usually diagnosed when patients reach their 20's. For some, it
may advance over several decades, for others, the progression may reach a
certain point and stop. Keratoconus is not usually visible to
the naked eye until the later stages of the disease. In severe
cases, the cone shape is visible to an observer when the patient looks
down while the upper lid is lifted. When looking down, the lower lid
is no longer shaped like an arc, but bows outward around the pointed
cornea. This is called Munson's sign.
Special
corneal testing called topography provides the doctor with detail about
the cornea's shape and is used to detect and monitor the progression of
the disease. A pachymeter may also be used to measure the thickness
of the cornea.
The first line of treatment for patients with keratoconus is to fit rigid
gas permeable (RGP) contact lenses. Because this type of contact is
not flexible, it creates a smooth, evenly shaped surface to see through.
However, because of the cornea's irregular shape, these lenses can be very
challenging to fit. This process often requires a great deal of time
and patience. When vision
deteriorates to the point that contact lenses no longer provide
satisfactory vision, corneal transplant may be necessary to replace the
diseased cornea with a healthy one.
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LASIK
is now the most popular of all laser vision correction procedures. The
first step in the LASIK procedure is the creation of a flap of tissue from
the outer layer of the central zone of the cornea
using the microkeratome. The flap is then folded back out of the way, but
it is held ready for replacement upon completion of the procedure. The
excimer laser is then used to sculpt the remaining central zone in
accordance with pre-determined data that has been entered into the laser
system’s computer. Under this precise control, the laser reshapes the
curvature of the cornea to correct for nearsightedness,
farsightedness or astigmatism.
This part of the procedure takes only 30 to 60 seconds, after which the
corneal flap is replaced. No sutures are used, and the surface of the eye
will normally heal itself. Most patients can see quite well within 24
hours or less. Complete healing of the cornea takes about one month.
The
LASIK procedure is performed on an outpatient basis. Although the actual
laser procedure takes only a few seconds per eye, the procedure requires a
couple of hours at the surgery center. Some of this time is spent
preparing the patient for the procedure, while a few minutes are required
afterwards for post-operative instructions and departure preparation.
How
is the procedure performed?
Step
1: Eye preparation
Before the procedure begins, a nurse or technician talks to the patient
about any immediate health problems that may affect readiness for the
procedure. Antibiotic and anesthetic eye drops are then placed in the eye
to numb it and prevent infection. The eye is swabbed with a sterile
solution. The eyelid is then propped open with a lid retainer, and a paper
or plastic "mask" is placed over the eye to keep eyelashes out
of the way. Then the cornea is marked with a blue "dye ring,"
which serves as a reference point for the surgeon throughout the
procedure. Because the cornea is numb, most patients experience little if
any discomfort during these pre-operative preparations.
Step
2: Creating the flap
Next, the doctor creates a flap from the central zone of the cornea using
the microkeratome. This precision instrument works much like a miniature
carpenter’s plane. It contains a disposable cutting blade that is preset
according to the thickness of the cornea — usually about 160 to 180
microns or 1/3 the depth of the cornea. The microkeratome operates in
conjunction with a suction ring that holds the eye perfectly still, and
when activated by a vacuum tube, it raises and flattens the cornea so it
can be reached easily for cutting the flap.
Step
3: The Excimer laser
After the flap has been folded back from the center of the eye, the doctor
dries the underlying cornea with a sponge-tipped swab and aligns the
Excimer laser’s microscope with the central corneal area in order to
monitor the laser’s sculpting pulsations. The patient is asked to focus
on a fuzzy red light inside the laser. As the doctor activates the laser,
there is a "popping" or "tacking" sound, and there is
a slight odor similar to that of hair burning, but no discomfort for the
patient. The number of laser pulsations will depend on the nature of the
refractive vision problem that is being corrected. This phase of the
procedure takes only a minute or so. The doctor then carefully folds the
flap back in place and irrigates the eye with a sterile saline solution.
The corneal area may be dried with a gentle blower, which helps seal the
flap. In addition, a contact lens may be placed in the eye.
Step
4: Post-operative measures
When the procedure is complete, additional antibiotic drops are placed in
the eye, and it may be covered with a plastic shield. For a short while
after the procedure, the eye is numb from the anesthetic drops. As the
numbness wears off, the patient may experience some light sensitivity and
a scratchy or dry sensation as though something is in the eye. This
feeling usually goes away within a few hours. Patients must not drive
themselves home following the procedure.
The
patient returns to the doctor’s office the next day for a post-operative
examination. The doctor checks the flap to see if it is healing properly.
If a contact lens was placed after surgery, it will be removed at this
time. Vision is checked and, for most patients will range from 20/20 to
20/40 depending on the number of laser pulsations received. For some
patients, vision may continue to improve for several weeks before totally
stabilizing.
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Macula
The
macula is a small area -- less than ¼ inch -- in the center of the retina
at the back of the eye (See Anatomy of
the Eye.). It is responsible for sharp, clear central vision
and the ability to perceive color.
How
does the macula function?
Like
the film in a camera, the retina receives light rays from the front of the
eye and transmits those light rays through the optic nerve to the brain
where the rays are converted into images. The densely packed photoreceptor
(light-sensitive) cells in the macula control all of the eye's central
vision and are responsible for the ability to read, drive a car, watch
television, see faces, and distinguish detail. The rest of the retina
handles peripheral vision that enables your eyes to see objects off to the
side while you are looking forward.
There
are two types of photoreceptor cells in the retina -- rods and cones. The
rods provide vision at low light levels, while the cones provide sharp
vision and discrimination. Because the macula contains a high
concentration of cones, straight-ahead vision is in sharp focus,
particularly in bright light. Most of the rods are located in the
periphery of the retina, so faint objects are more visible if you do not
look directly at them. A dim star, for instance, is best seen when your
eyes are not aimed directly at it.
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Macular
Degeneration
Age-related
macular degeneration is a progressive disorder of the tiny central part of
the retina, called the macula (See Anatomy
of the Eye), that gradually destroys central vision, making
reading or driving difficult or impossible. Although some peripheral
vision remains, a person with macular degeneration has increasing
difficulty in reading, watching television, or even recognizing friends.
Because
it is an age-related disease, the incidence of macular degeneration is
growing as the mature population increases. An estimated 400,000 Americans
develop a serious form of the disease every year.
What
causes Macular Degeneration? What are the risk factors?
Although
the macula occupies only 2 percent of the retina, it contains about 25
percent of the light-sensing cone cells, which are specialized for
daylight vision. macular degeneration occurs when this central part of the
retina and the layer of cells underneath it, which is the retinal pigment
epithelium, begin to deteriorate, for reasons that are not clear. Genetics
may play a role in some cases, because the disease can run in families.
There
are two forms of macular degeneration, dry and wet. The "dry"
form, which accounts for 85 percent to 90 percent of all cases, does not
cause blindness but does cause a loss of central vision that can produce
grayness, haziness, or a blind spot in the central area of vision. In the
dry form of the disease, tiny white deposits called drusen accumulate in
the retina, and there is a thinning of macular tissue. The cause is
unknown, although lifetime exposure to sunlight and smoking may increase
the risk. In "wet" macular degeneration cases, which account for
10 percent to 15 percent of all cases, abnormal blood vessels grow under
the retina, scarring or destroying retinal tissue and often causing sudden
blindness. The wet form causes most macular degeneration-related
blindness.
What
are the symptoms?
The
symptoms of macular degeneration are blurred vision, loss of color
perception, a dark or empty spot in the center of the field of vision, and
seeing crooked lines that are really straight. The condition can be
diagnosed in several ways: with an ophthalmoscope, a slit lamp lens, an
Amsler Grid test, photographing the back of the eye, fluorescein
angiography, and/or macular pigment density testing. People over the age
of 65 are advised to see an ophthalmologist once a year for a complete eye
examination, and any sudden change in vision should be reported to an
ophthalmologist. If dry macular degeneration is detected, close follow-up
is recommended to monitor for indications of the wet form.
What
treatments are recommended for macular degeneration?
Several
techniques are used to treat wet macular degeneration:
-
Laser
photocoagulation surgery uses a powerful beam of light to attack the
abnormal blood vessels. Early diagnosis is important because this
treatment is effective only in the early stages of the disease. The
surgery often does not stop the progression of abnormal blood vessels,
so repeat treatments are needed. The surgery can destroy some healthy
tissue, causing some loss of vision.
-
Still
somewhat experimental, photodynamic therapy uses verteporfin (brand
name Visudyne), a photosensitive dye that goes to the abnormal blood
vessels. Light from a low-powered laser triggers a chemical reaction
that destroys the blood vessels. Photodynamic therapy generates less
heat than photocoagulation, and thus causes less damage to healthy
tissue.
-
Another
treatment involves surgery to detach the retina and rotate it, so that
the macula is no longer in the region of abnormal blood vessel growth.
-
Surgery
can also be used to remove the abnormal blood vessels.
-
Thalidomide,
notorious for causing birth defects, is being tried as a treatment
because it blocks blood vessel development.
What
can be done to decrease the likelihood of developing macular degeneration?
There
is evidence that chemicals called antioxidants, which include vitamins C
and E, can protect the macula. So can carotenoids, which include
beta-carotene, and the mineral selenium. Field trials to determine whether
vitamin therapy can be effective against macular degeneration have begun.
The National Institutes of Health has started a study to determine whether
estrogen replacement after the menopause can prevent or slow the
progression of macular degeneration.
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Nearsightedness,
or Myopia
Nearsightedness,
or myopia, is the ability of the eye to clearly see objects that are up
close, but not far away. A nearsighted person can usually see well to
read, but has trouble with distance vision, such as that used in driving.
This is a common refractive eye condition created when the eyeball is more
elongated than normal from front to back, or the cornea is too steep or
dome-shaped. Myopia is an inherited condition that affects about one
person in five.
In
a myopic eye, the light rays are passed through the cornea and lens but
the point at which they converge (focus) is in front of the retina, not on
the retina. This configuration allows clear images of near objects but not
those that are far away. Non- surgical treatment options for myopia
include glasses and contact lenses.
Surgical treatment options include clear lens extraction or LASIK
surgery. 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 eye doctor prior to making
any final decisions.
 
How
is nearsightedness corrected?
The
usual treatment for nearsightedness is prescription eyeglasses with
concave (inwardly curved) lenses or contact lenses that counteract the
distortion created by corneas that are too outwardly curved in shape. A
concave lens moves the image of a distant object backward onto the retina,
thereby bringing it into proper focus.
Refractive
eye surgery, which flattens the cornea, has also become a popular option
for the correction of nearsightedness in recent years. The most popular of
those procedures is LASIK, (Laser In-Situ
Keratomileusis) which uses an Excimer laser to reshape the cornea,
often eliminating the need for corrective lenses. Another option that is
becoming popular is Intrastromal Corneal Ring Segments (ICRSs), tiny
plastic arcs that are implanted in the peripheral area of the cornea,
causing the center of the cornea to flatten. These segments can be removed
and/or replaced if needed. Refractive eye surgery is usually not
recommended for people under 18 years of age.
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Ocular
hypertension
Ocular
hypertension occurs when the intraocular pressure in your eyes is above
the normal range, but it has not yet affected your vision or damaged the
structure of your eyes. Normal eye pressure usually ranges between 10 and
21 mm of mercury. Pressure consistently above 21 indicates ocular
hypertension. The condition can develop into glaucoma,
a serious disease that causes damage to the optic nerve.
Who
is at risk for ocular hypertension?
Most
at risk for developing ocular hypertension are African Americans and those
with a family history of the condition. It is also more common in those
who are nearsighted, have high blood
pressure, or are diabetic. Because ocular hypertension has no outward
symptoms, people over the age of 40 and those in a high-risk category for
glaucoma should have their pressure checked every year. A pressure check
is a painless procedure that is part of any comprehensive eye examination.
What
causes ocular hypertension?
In
simple terms, ocular hypertension is caused by an excessive buildup of
fluid inside the eye. This fluid, or aqueous humor, nourishes the cornea,
iris, and lens, and maintains intraocular pressure. The typical eye
produces about 4 c.c. of fluid a day, which circulates and then drains out
of the eye If the drainage system becomes clogged or if too much fluid is
produced, pressure inside the eye can build up. The reasons for this are
not fully understood.
There
are normally no symptoms of ocular hypertension, which is one of the
reasons why regular eye examinations are so important. Although ocular
hypertension in itself is not sight threatening, if pressure within the
eye builds to the point where it damages the optic nerve (glaucoma),
eyesight can be permanently damaged.
How
is ocular hypertension checked?
An
instrument called a tonometer is used to check eye pressure. There are two
types of tonometers. One is called an applanation
tonometer and uses an instrument that looks somewhat like a pen. After
numbing eyedrops are administered, the instrument is applied gently to the
front surface of the eye and provides a pressure reading. The other type
is a noncontact tonometer, which directs a warm puff of air toward the eye
without touching it.
Neither
ocular hypertension nor glaucoma can be prevented or cured, and ocular
hypertension does not usually require treatment unless it progresses to
glaucoma. Some doctors may, however, treat the condition with eye drops or
other medicines as a precautionary measure. After you are diagnosed with
ocular hypertension, your eye health must be monitored closely.
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Presbyopia
Presbyopia,
also known as the “short arm syndrome,” is a term used to describe an
eye in which the natural lens can no longer accommodate.
Accommodation is the eye’s way of changing its focusing distance:
the lens thickens, increasing its ability to focus close-up. At
about the age of 40, the lens becomes less flexible and accommodation is
gradually lost. It’s a normal process that everyone eventually
experiences.
Most
people first notice difficulty reading very fine print such as the phone
book, a medicine bottle, or the stock market page. Print seems to
have less contrast and the eyes become easily fatigued when reading a book
or computer screen. Early on, holding reading material further away
helps for many patients. But eventually, reading correction in the
form of reading glasses, bifocals, or contact lenses is needed for close
work. However, nearsighted people can simply take their glasses off
because they see best close-up.
Signs and Symptoms
·
Difficulty seeing clearly for close work
·
Print seems to have less contrast
·
Brighter, more direct light required for reading
·
Reading material must be held further away to see (for some)
·
Fatigue and eyestrain when reading
Presbyopia
is detected with vision testing and a refraction. The treatment for
presbyopia is very simple, but is entirely dependent on the individual’s
age, lifestyle, occupation, and hobbies. If the patient has good
distance vision and only has difficulty seeing up close, reading glasses
are usually the easiest solution. For others, bifocals (glasses with
reading and distance correction) or separate pairs of reading and distance
glasses are necessary. Another option is monovision: adjusting
one eye for distance vision, and the fellow eye for reading vision.
This can be done with contact lenses or permanently with refractive
surgery.
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Retina,
diseases of the retina
The
retina is the light-sensitive membrane that covers the inside of the back of the
eye. It receives the images that come through the cornea and lens. The retina
contains light-sensitive nerve cells, the rods and cones, which send nerve
impulses along the optic nerve to the brain by way of a network of connecting
and integrating cells, some of which have very long fibers.
The
rods and cones are specialized for different purposes. The rods perceive light,
while the cone cells perceive both light and color. The retina has 20 times more
rod cells than cone cells. Because there are fewer cone cells and because they
need more light to function, it is difficult to discern colors in dim light.
At
the center of the retina is an area called the fovea, which has no blood
vessels. Light-sensitive cells, primarily cones, are packed tightly in the
fovea, so that it has the highest visual resolution.
How
is the retina examined?
When
conducting an eye examination, the examiner uses the ophthalmoscope, a hand-held
device with a bright light, to examine the retina. The eye care professional
looks for such abnormal conditions as damage to the tiny blood vessels that can
be caused by high blood pressure or diabetes, detachment of the retina from the
back of the eyeball, or blank spots on surface of the eyeball.
What
causes retinal damage?
Heavy
drinking and cigarette smoking, along with poor nutrition, can also lead to
retinal damage, as can vitamin deficiency and lead poisoning.
What
are some other retinal diseases and disorders?
Retinitis
pigmentosa
This is a gradual degeneration of the rods and cones that can begin as early as
adolescence but most commonly occurs in middle age.
Tay-Sachs
disease
Tay-Sachs affects not only the eye but also the brain, causing early death.
Age-related
macular degeneration
An age-related retinal disorder is macular degeneration, gradual deterioration
of the innermost part of the retina, the macula. There are two kinds of macular
generation, wet and dry. In both kinds, there is a gradual breakdown of cells of
the macula and the layer of cells below it, the retinal pigment epithelium.
The
"dry" form is most common, accounting for about 90 percent of cases.
Progressive breakdown of the cells causes a blind spot in the center of the eye.
The "wet" form is caused by an overgrowth of blood cells in the area
of the macula. Wet macular degeneration can be treated to some extent, but the
dry form is currently untreatable.
Retinopathy
Retinopathy is a term used to describe a variety of disorders of the retina.
One
form is diabetic retinopathy, damage to the retina and the blood vessels that
serve it when diabetes is not well controlled. The blood vessels can leak or
burst, new vessels can grow on the surface of the retina, and there can be
abnormal growth of fibrous tissue. Diabetic retinopathy is a major cause of loss
of vision.
Hypertensive
retinopathy results from high blood pressure, which causes the retinal blood
vessels to become abnormally narrow.
Atherosclerosis
of the retinal artery, the same kind of blood vessel blockage that leads to
heart attack and stroke, can cause severe damage to the retina.
Retinal
vein occlusion is a common cause of blindness. It happens when the central vein
or artery of the retina is blocked.
Retinal
tear and detachment
Retinal tear is a split in the retina that usually is caused by gradual
degeneration. It is common in persons with severe nearsightedness, who have
thinner-than-normal retinas. It can also be caused by a severe eye injury. A
retinal tear often is followed by retinal detachment, in which the vitreous
fluid of the eye collects between the delicate nerve membrane and the underlying
layer of pigment.
Because it can cause devastating damage to the vision if left untreated,
retinal detachment is considered an ocular emergency that requires
immediate medical attention and surgery. It is a problem that occurs
most frequently in the middle-aged and elderly. Symptoms of a
retinal detachment include light flashes, wavy vision, a "veil"
obstructing peripheral vision, shower of floaters that resembel spots,
bugs, or spider webs, and sudden decrease in vision. Early
detection is key in successfully treating retinal detachments and tears.
Awareness of the quality of your vision in each eye is extremely
important, especially if you are in a higher-risk group such as those who
are nearsighted or diabetic. Compare the vision of your eyes daily
by looking straight ahead and covering one eye and then the other. Retinoblastoma
Retinoblastoma is a cancer that occurs early in childhood and has a genetic
basis. It occurs in about one of every 20,000 births. It can be treated by
radiation but most often requires surgical removal of the affected eye. If both
eyes are affected, one may be removed, and the other may receive radiation
therapy.
Retinal
infections
The retina is also subject to infection.
One
common infection is toxoplasmosis, caused by a parasite that is found in raw
beef and cat feces. The infection often occurs before birth, and it causes
progressive retinal damage over the years.
Other
infections include toxocara canis, in which worm larvae lodge in the retina,
causing severe damage, and onchocerciasis, another worm infestation.
Bacterial
or viral infections elsewhere in the body may also be carried to the retina.
They pose a special danger for persons with impaired immune systems.
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Strabismus
Strabismus
is a functional defect where the eyes are misaligned and point in
different directions. The brain’s ability to see three-dimensional
objects depends on proper alignment of the eyes. When both eyes are
properly aligned and aimed at the same target, the visual portion of the
brain fuses the forms into a single image. When one eye turns inward,
outward, upward, or downward, two different pictures are sent to the
brain. This causes loss of depth perception and binocularity,
or normal two-eyed vision. The turned eye may be straight at times, and the
misalignment may come and go. Strabismus occurs in about 4 percent of all
children in the United States, equally in males and females, and is
sometimes hereditary. The condition can also develop later in life.
There
are two forms of strabismus, esotropia and exotropia.
In esotropia, one eye deviates inward toward the nose, while in exotropia,
one eye deviates outward away from the nose. Esotropia is the most common
type of strabismus in infants, while exotropia often begins between the
ages of 2 and 4.

In
young children with any form of strabismus, the brain may learn to ignore
the misaligned eye’s image and see only the image from the best-seeing
eye. This is called amblyopia, or lazy eye, and
results in a loss of depth perception. When an adult develops strabismus,
double vision sometimes occurs because the brain has already been trained
to receive images from both eyes and cannot ignore the image from the
turned eye.
What
makes strabismus occur?
The
causes of strabismus are not fully understood. There are six muscles that
control eye movement, four that move it up and down and two that move it
side to side. All these muscles must be coordinated and working properly
in order for the brain to see a single image. When one or more of these
muscles doesn’t work properly, some form of strabismus may occur.
Strabismus is more common in children with disorders that affect the brain
such as cerebral palsy, Down syndrome, hydrocephalus, and brain tumors.
What
are the signs of strabismus?
The
earliest sign of strabismus is usually a noticeable deviation of one eye.
This symptom may at first be intermittent, occurring when a child is
daydreaming, not feeling well, or tired. The deviation may also be more
noticeable when the child looks at something in the distance. Frequent
rubbing of the eyes is also common with strabismus. In bright light,
children may squint or tilt their heads in order to use both eyes
together. Few children ever complain about double vision, although they
may close one eye to compensate for the problem.
The
eyes of infants and small children can sometimes seem to be crossed when
they have a wide, flat nose and a fold of skin at the inner eyelid. Called
false strabismus, it usually disappears as the child grows. True
strabismus will not be outgrown. An eye doctor can tell the difference
between true and false strabismus.
How
is strabismus detected and treated?
To
diagnose strabismus, an eye doctor will perform a comprehensive eye
examination including an ocular motility (eye movement) evaluation, an
evaluation of the internal ocular structures, and a cover test to evaluate
eye alignment. The most reliable treatment for strabismus is usually
vision therapy and eye patching and/or eyeglass therapy, especially if amblyopia
(lazy eye) is present. This therapy is designed to maximize the existing
vision in the “bad” eye and train the eyes to work together. In
some children, eye muscle surgery may also be necessary.
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A
Stye
A
stye (chalazion) is a small lump in the eyelid caused by obstruction of an
oil producing or meibomian gland. A stye may occur in the upper or
lower lids, causing redness, swelling and soreness in some cases.
Symptoms include raised, swollen bump on the upper or lower eye lid that
is often red and may be tender and sore
In
the early stages, a stye may be treated at home with the repeated use of
warm compresses for 15 - 20 minutes followed by several minutes of light
lid massage. This helps to reduce the swelling and makes the lid
more comfortable. However, if the stye does not diminish or recurs,
medical attention may be necessary. This may include draining the
stye along with the use of antibiotic and anti-inflammatory medications.
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