What are refractive errors?
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 (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.
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 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.
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. Refractive surgery is also an option to
correct or improve your vision. These surgical procedures
are used to permanently adjust your eye's focus by reshaping
the cornea, or front surface 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 out UV 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 at a 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 at a distance,
you can receive a prescription for reading glasses or
buy then over the counter 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.
Refractive surgery
Photorefractive keratectomy (PRK)
The excimer laser is used to reduce myopia, astigmatism,
and hyperopia in a procedure called photorefractive
keratectomy (PRK). Using an invisible, high-energy light,
the laser precisely sculpts the cornea. No surgical
blades are used in PRK.
Laser in-situ keratomileusis (LASIK)
LASIK is a combined microsurgical and excimer laser
procedure to correct myopia and astigmatism. In LASIK,
a highly specialized instrument (microkeratome) is used
to make a thin flap in the cornea. This flap is folded
back, and excimer laser is then applied to the cornea
under the flap to correct myopia and astigmatism. The
flap is then replaced and allowed to heal back into
position. There are no stitches used in this procedure.
Complications and side effects
Refractive surgery is elective surgery so it is very
important to make an informed decision, should you decide
to have it. Complications and side effects of these
procedures include:
-
temporary discomfort
-
blurry and fluctuating vision
-
glare and haloes
-
need for reading glasses
-
under and over-correction
-
poor night vision
-
irregular astigmatism
-
difficulty fitting contact lenses
-
corneal scarring
-
permanent vision loss.
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 on which correction will be most effective
for you.
|
