Myopia (Nearsightedness)
Myopia FAQs
What causes nearsightedness?
How is nearsightedness diagnosed?
How is nearsightedness treated?
Nearsightedness, or myopia, as it is medically termed, is a vision
condition in which close objects are seen clearly, but objects
farther away appear blurred. Nearsightedness occurs if the eyeball
is too long or the cornea, the clear front cover of the eye, has
too much curvature. As a result, the light entering the eye isn’t
focused correctly and distant objects look blurred.
Nearsightedness is a very common vision condition affecting nearly
30 percent of the U.S. population. Some research supports the
theory that nearsightedness is hereditary. There is also growing
evidence that it is influenced by the visual stress of too much
close work.
Generally, nearsightedness first occurs in school-age children.
Because the eye continues to grow during childhood, it typically
progresses until about age 20. However, nearsightedness may also
develop in adults due to visual stress or health conditions such
as diabetes.
A common sign of nearsightedness is difficulty with the clarity of
distant objects like a movie or TV screen or the chalkboard in
school. A comprehensive optometric examination will include
testing for nearsightedness. An optometrist can prescribe
eyeglasses or contact lenses that correct nearsightedness by
bending the visual images that enter the eyes, focusing the images
correctly at the back of the eye. Depending on the amount of
nearsightedness, you may only need to wear glasses or contact
lenses for certain activities, like watching a movie or driving a
car. Or, if you are very nearsighted, they may need to be worn all
the time.
Another option for treating nearsightedness is orthokeratology (ortho-k),
also known as corneal refractive therapy. It is a non-surgical
procedure that involves wearing a series of specially designed
rigid contact lenses to gradually reshape the curvature of your
cornea. The lenses place pressure on the cornea to flatten it.
This changes how light entering the eye is focused.
Laser procedures are also a possible treatment for nearsightedness
in adults. They involve reshaping the cornea by removing a small
amount of eye tissue. This is accomplished by using a highly
focused laser beam on the surface of the eye.
For people with higher levels of nearsightedness, other refractive
surgery procedures are now available. These procedures involve
implanting a small lens with the desired optical correction
directly inside the eye, either just in front of the natural lens
(phakic intraocular lens implant) or replacing the natural lens
(clear lens extraction with intraocular lens implantation). These
procedures are similar to one used for cataract surgery patients,
who also have lenses implanted in their eyes (intraocular lens
implants).
What causes nearsightedness?
The tendency to develop myopia may be inherited.
If one or both parents are nearsighted, there is an increased
chance their children will be nearsighted.
The exact cause of nearsightedness is unknown, but two factors
may be primarily responsible for its development:
heredity
visual stress
There is significant evidence that many people inherit
nearsightedness, or at least the tendency to develop
nearsightedness. If one or both parents are nearsighted, there is
an increased chance their children will be nearsighted.
Even though the tendency to develop nearsightedness may be
inherited, its actual development may be affected by how a person
uses his or her eyes. Individuals who spend considerable time
reading, working at a computer, or doing other intense close
visual work may be more likely to develop nearsightedness.
Nearsightedness may also occur due to environmental factors or
other health problems:
Some people may experience blurred distance vision only at night.
This “night myopia” may be due to the low level of light making it
difficult for the eyes to focus properly or the increased pupil
size during dark conditions, allowing more peripheral, unfocused
light rays to enter the eye.
People who do an excessive amount of near vision work may
experience a false or “pseudo” myopia. Their blurred distance
vision is caused by over use of the eyes’ focusing mechanism.
After long periods of near work, their eyes are unable to refocus
to see clearly in the distance. The symptoms are usually temporary
and clear distance vision may return after resting the eyes.
However, over time constant visual stress may lead to a permanent
reduction in distance vision.
Symptoms of nearsightedness may also be a sign of variations in
blood sugar levels in persons with diabetes or an early indication
of a developing cataract.
An optometrist can evaluate vision and determine the cause of the
vision problems.
How is nearsightedness diagnosed?
Testing for nearsightedness may use several procedures in order to
measure how the eyes focus light and to determine the power of any
optical lenses needed to correct the reduced vision.
A phoropter and retinoscope
A phoropter and retinoscope are often used to determine the lenses
that allow the clearest vision during a comprehensive eye exam.
As part of the testing, letters on a distance chart are
identified. This test measures visual acuity, which is written as
a fraction such as 20/40. The top number of the fraction is the
standard distance at which testing is performed, twenty feet. The
bottom number is the smallest letter size read. A person with
20/40 visual acuity would have to get within 20 feet to identify a
letter that could be seen clearly at forty feet in a “normal” eye.
Normal distance visual acuity is 20/20, although many people have
20/15 (better) vision.
Using an instrument called a phoropter, an optometrist places a
series of lenses in front of your eyes and measures how they focus
light using a hand held lighted instrument called a retinoscope.
The doctor may choose to use an automated instrument that
automatically evaluates the focusing power of the eye. The power
is then refined by patient’s responses to determine the lenses
that allow the clearest vision.
This testing may be done without the use of eye drops to determine
how the eyes respond under normal seeing conditions. In some
cases, such as for patients who can’t respond verbally, or when
some of the eye’s focusing power may be hidden, eye drops may be
used. They temporarily keep the eyes from changing focus while
testing is performed.
Using the information obtained from these tests, along with the
results of other tests of eye focusing and eye teaming, your
optometrist can determine if you have nearsightedness. He or she
will also determine the power of any lens correction needed to
provide clear vision. Once testing is complete, your optometrist
can discuss options for treatment.
How is nearsightedness treated?
Persons with nearsightedness have several options available to
regain clear distance vision. They include:
eyeglasses
contact lenses
orthokeratology
laser and other refractive surgery procedures
vision therapy for persons with stress-related nearsightedness.
Eyeglasses are the primary choice of correction for persons with
nearsightedness. Generally, a single vision lens is prescribed to
provide clear vision at all distances. However, for patients over
about age 40, or children and adults whose nearsightedness is due
to the stress of near vision work, a bifocal or progressive
addition lens may be needed. These multifocal lenses provide
different powers or strengths throughout the lens to allow for
clear vision in the distance and also clear vision up close.
Girl with eyeglasses
Eyeglasses are frequently used to correct
myopia.
A large selection of lens types and frame designs are now
available for patients of all ages. Eye glasses are no longer just
a medical device that provides needed vision correction, but can
also be a fashion statement. They are available in a wide variety
of sizes, shapes, colors and materials that not only correct for
vision problems but also may enhance appearance.
For some individuals, contact lenses can offer better vision than
eyeglasses. They may provide clearer vision and a wider field of
view. However, since contact lenses are worn directly on the eyes,
they require regular cleaning and care to safeguard eye health.
Orthokeratology (Ortho-k), also known as corneal refractive
therapy, involves the fitting of a series of rigid contact lenses
to reshape the cornea, the front outer surface of the eye. The
contact lenses are worn daily for limited periods, such as
overnight, and then removed. Persons with moderate amounts of
nearsightedness may be able to temporarily obtain clear vision for
most of their daily activities.
Nearsightedness can also be corrected by reshaping the cornea
using a laser beam of light. Two commonly used procedures are
photorefractive keratectomy (PRK) and laser in situ keratomileusis
(LASIK).
In PRK, a laser is used to remove a thin layer of tissue from the
surface of the cornea in order to change its shape and refocus
light entering the eye. There is a limit to how much tissue can
safely be removed and therefore the amount of nearsightedness that
can be corrected.
LASIK does not remove tissue from the surface of the cornea, but
from its inner layers. To do this, a section of the outer corneal
surface is cut and folded back to expose the inner tissue. Then a
laser is used to remove the precise amount of corneal tissue
needed to reshape the eye, and then the flap of outer tissue is
placed back in position to heal. The amount of nearsightedness
that LASIK can correct is limited by the amount of corneal tissue
that can be removed in a safe manner.
People who are highly nearsighted or whose corneas are too thin to
allow the use of laser procedures now have another option. They
may be able to have their nearsightedness surgically corrected by
implanting small lenses in their eyes. These intraocular lenses
look like small contact lenses and they provide the needed optical
correction directly inside the eye.
Vision therapy is an option for people whose blurred distance
vision is caused by a spasm of the muscles which control eye
focusing. Various eye exercises can be used to improve poor eye
focusing ability and regain clear distance vision.
People with nearsightedness have a variety of options to correct
their vision problem. In consultation with your optometrist, you
can select the treatment that best meets you visual and lifestyle
needs.
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