For our eyes to be able to see, light
rays must be bent or "refracted" so they can focus
on the retina, the nerve layer that lines the back of the
eye. The cornea and the lens refract
light rays. The retina receives the picture formed by these
light rays and sends the image to the brain through the optic
nerve. A refractive error means
that the shape of your eye doesn't refract the light properly,
so that the image you see is blurred. While
refractive errors are called eye disorders, they are not diseases.
What are the different types of
refractive errors?
Myopia rs(nearsightedness)
A myopic eye is longer than normal, so
that the light rays focus in front of the retina. Close objects
look clear but distant objects appear blurred.
In myopia, distant objects are blurry
because the eye is too long, and images focus in front of
the retina instead of on it.
Myopia is inherited and is often discovered
in children when they are eight to twelve years old. During
the teenage years, when the body grows rapidly, myopia gets
worse. Between the ages of 20 and 40, there is usually little
change. If the myopia is mild, it
is called low myopia. Severe myopia is known as high myopia.
If you have high myopia, you have a higher
risk of detached retina. It is important to have regular eye
examinations by an ophthalmologist (medical eye doctor) to
watch for any changes in the retina. If the retina does detach,
a surgical operation is the only way to repair it.
Hyperopia (farsightedness)
A hyperopic eye is shorter than normal.
Light from close objects, such as the page of a book, cannot
focus clearly on the retina. In
hyperopia, the eye is too short for images to focus on the
retina, so close objects are blurry. Like
nearsightedness, farsightedness is usually inherited. Babies
and young children tend to be slightly hyperopic. As the eye
grows and becomes longer, hyperopia lessens.
Astigmatism (distorted vision)
The cornea is the clear front window of
the eye. A normal cornea is round and smooth, like a basketball.
When you have astigmatism, the cornea curves more in one direction
than in the other, like a football.
Astigmatism distorts or blurs vision for
both near and far objects. It's almost like looking into a
funhouse mirror in which you appear too tall, too wide or
too thin. You can have astigmatism in combination with myopia
or hyperopia.
Presbyopia
(aging eyes)
When you are young, the lens in your eye
is soft and flexible. The lens of the eye changes its shape
easily, allowing you to focus on objects both close and far
away.
After the age of 40, the lens becomes
more rigid. Because the lens can't change shape as easily
as it once did, it is more difficult to read at close range.
This perfectly normal condition is called presbyopia.
You can also have presbyopia in combination
with myopia, hyperopia or astigmatism.
How are refractive errors corrected?
Eyeglasses or contact lenses are the most
common methods of correcting refractive errors. They work
by refocusing light rays on the retina, compensating for the
shape of your eye.
There is no scientific evidence that eye
exercises, vitamins or pills can prevent or cure refractive
errors.
Eyeglasses
Glasses are an easy method to correct
refractive errors. They can also help protect your eyes from
harmful light rays, such as ultraviolet (UV) light rays. A
special coating that screens ou tUV light is available when
you order your glasses.
Bifocals are glasses that are used to
correct presbyopia. They have a correction for reading on
the bottom half of the lens and another for seeing distance
on the top. Trifocals are lenses with three different lens
corrections in one set of eyeglasses.
If you don't need correction for seeing
distance, you can buy over-the-counter reading glasses to
correct presbyopia.
No exercise or medication can reverse
presbyopia. You will probably need to change your prescription
from time to time between the ages of 40 and 60, because your
lens will continue to lose flexibility.
Contact
lenses
There are now a wide variety of contact
lenses available. The type that is best for you depends on
your refractive error and your lifestyle. If you want to wear
contact lenses, discuss the various options with your ophthalmologist.
You may have heard of a process called
orthokeratology to treat myopia. It uses a series of hard
contact lenses to gradually flatten the cornea and reduce
the refractive error.
Improvement of sight from orthokeratology
is temporary. After the use of the lenses is discontinued,
the cornea returns to its original shape and myopia returns.
Photorefractive keratectomy
(PRK)
In the past few years a new type of laser
surgery has been investigated to correct myopia. In a process
called photorefractive keratectomy (PRK), the excimer laser
precisely sculpts the surface of the cornea.
There are several thousand people in the
United States who have had PRK through research studies overseen
by the Food and Drug Administration. For mild to moderate
myopia, PRK and RK have similar results.
What is the best method
of correcting refractive errors?
There is no "best" method for
correcting refractive errors. The most appropriate correction
for you depends on your eyes and your lifestyle. You should
discuss your refractive errors and your lifestyle with your
ophthalmologist to decide which correction will be most effective
for you.
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