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What are refractive errors?
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| Normal |
Astigamatism |
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| Hyperopia |
Myopia |
The cornea and lens bend or refract
light rays so they can be focused on the
retina, the nerve layer that lines the
back of the eye. The retina receives the
picture formed by these light rays and
sends the image to the brain through the
optic nerve. A refractive error means
that the shape of the eye does not allow
the light to be properly refracted
making images blurry. Refractive errors
include:
- myopia (nearsightedness)
- hyperopia (farsightedness)
- astigmatism
- presbyopia
- monovision
What is myopia (nearsightedness)?
Myopia (nearsightedness) occurs when
light rays are focused in front of the
retina instead of directly on the
retina. Myopia is a vision problem
experienced by approximately one-third
of the population. When the eyeball is
too long from front to back, the image
of a distant object focuses in front of
the retina, instead of directly on it.
As a result, the distant object appears
blurred. The more myopic the eye, the
closer an object must be before it is in
sharp focus. Nearsighted people have
difficulty seeing objects at a distance,
such as highway signs, but usually can
see up-close for tasks such as reading
or sewing.
Some people with
myopia can use their natural
nearsightedness to read without glasses
at an age when other people must wear
reading glasses. However, if they have
refractive surgery to correct myopia,
they may be able to see distant objects
without glasses, but will probably need
to wear glasses to read sometime after
age 40, due to presbyopia.
What are signs of myopia?
Nearsighted people may experience headaches or eyestrain and might squint or feel fatigued when driving or playing sports. Patients who experience these symptoms while wearing glasses or contact lenses may need a comprehensive eye examination, as well as a new prescription.
What causes myopia?
Nearsightedness runs in families and
usually appears in childhood. This
vision problem may stabilize at a
certain point, although sometimes it
worsens with age. This is known as
"myopic creep."
What is the treatment for myopia?
Non-surgical treatment options for myopia include glasses and contact lenses. Surgical treatment options include, clear lens extraction, LASEK, LASIK, LASEK, phakic IOL and. While there are numerous surgical options available, not all individuals are good candidates for specific procedures. Patients should review these options in depth with their physicians prior to making any final decisions.
What is hyperopia (farsightedness)?
Hyperopia or farsightedness occurs when
light rays are not bent enough to focus
on the retina. Hyperopia is a common
vision problem, affecting about
one-fourth of the population. If the eye
is too short from front to back, light
rays reach the retina before they
converge (focus). People with hyperopia
can sometimes see distant objects very
well, but may have difficulty seeing
objects that are close.
Young
eyes can sometimes compensate for this
refractive error --- depending on age
and the degree of hyperopia present. But
with aging, the human lens loses this
ability and a hyperopic person
eventually may have difficulty seeing
objects at a distance, as well as those
that are nearby. In fact by age 40, even
those with little or no refractive error
will begin to experience difficulty
focusing on close objects.
What are signs of hyperopia?
Farsighted people sometimes have
headaches or eyestrain, and may squint
or feel fatigued when performing work at
close range. Patients who experience
these symptoms while wearing glasses or
contact lenses may need an eye exam and
a new prescription.
What causes hyperopia?
Most children are born with hyperopia, but most of them "outgrow" it as the eyeball lengthens with normal growth. Sometimes people confuse hyperopia with astigmatism; both cause difficulty in seeing close objects, but have different causes.
What is the treatment for hyperopia?
Non-surgical treatment options include glasses and contact lenses. Surgical treatment options include clear lens extraction, LASIK, phakic IOL, and PRK. While there are numerous surgical options available, not all individuals are good candidates for specific procedures. Patients should review these options in depth with their physicians prior to making any final decisions.
What is astigmatism?
Regular astigmatism occurs when light rays are focused at more than one point on the retina. Astigmatism is the most common vision problem. It occurs when the cornea surface is not ideally rounded, but is curved more along one axis than the other --- that is, when the eye is shaped more like the side of a football than a basketball. Light entering the eye does not focus symmetrically on the retina. The result is astigmatism, which blurs both near and distance vision. This refractive error may occur in patients who are either myopic (nearsighted) or hyperopic (farsighted). There are various types of astigmatism included regular, mixed and irregular astigmatism.
What are the signs of astigmatism?
Patients with only a small amount of
astigmatism may not notice it or may
have slightly blurred vision. Sometimes
uncorrected astigmatism can cause
headaches or eyestrain and distort or
blur vision.
Eyeglasses or
contact lens prescriptions with three
parts indicate some amount of
astigmatism. A prescription with three
parts looks like this: -2.75 -1.25 x
180. The first part indicates the main
spherical correction, while parts two
and three show the extent and location
of your astigmatism.
What is presbyopia (age-related difficulty with near vision)?
With increasing age, the lens inside of
the eyes loses the ability to focus on
nearby objects. The problem usually
manifests itself around age 40 and can
be corrected with bifocals or reading
glasses. This is a normal aging process,
called presbyopia and all people
develop.
Some people with myopia
can use their natural nearsightedness to
read without glasses at an age when
other people must wear reading glasses.
However, if they have refractive surgery
to correct myopia, they will be able to
see distant objects without glasses, but
probably will need to wear glasses to
read sometime after age 40 due to
presbyopia.
What is monovision?
Monovision is a method of distance vision correction to account for presbyopia. In monovision, refractive surgery is used to adjust one eye for "near" vision and the other eye for "distance" vision. Contact lenses or glasses may be required for best distance or night vision activities, including driving. This option is not suitable for everyone and a trial period of monovision using contact lenses may help decide if it is right for the pasient) |
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