Understanding The Treatment For
Farsightedness
If you are farsighted, or hyperopic,
light comes to an imaginary focal point behind your retina. The
farsighted eyeball is too short from front to back for the
power of the cornea, causing a blurred image up close. (The
length of your eye may be too short from front to back, or your
cornea may be flatter than normal, or both.) Almost all newborn
babies are farsighted; those who aren't often become markedly
nearsighted as adults. Since many hyperopic patients can see
distant objects well when they are young, they are called
farsighted.
To correct farsightedness, a laser surgeon makes the center
of the eye's window steeper by removing tissue in a carefully
blended circular pattern around the mid-periphery of the
cornea. Even though the laser is not aimed at the
line-of-sight, the effect of treatment is directly over the
pupil. After surgery, the central cornea has a steeper curve
with more light blending ability that can focus incoming light
nearer the retina instead of behind it. Although both hyperopic
and myopic LASIK procedures remove tissue to the same depth for
the same number of diopters of refractive error, much more
tissue is removed from the cornea to treat farsightedness.
Refractive surgery for farsightedness can improve both near and
distance vision, although you may still need glasses to read if
you are over forty.
While it is true that the farsighted eye focuses light at a
theoretical point beyond the retina, hyperopia is more complex
than this brief explanation implies. Without the added light
bending power of the flexible crystalline lens inside your eye,
even parallel light rays reflected off distant objects "focus"
behind your sensitive photoreceptors. Causing an even more
blurred image, the divergent rays from close objects "come
together" still further behind your retina than light from far
away.
So to help you understand farsightedness on a practical
level, you need to keep in mind how the two lenses of your eye
- your powerful fixed corneal lens and your adjustable
crystalline lens inside your eye - work together to focus
light. In the youthful eye, the flexible crystalline lens can
"morph" itself, becoming thicker to bring close objects into
view and remaining flatter to look in the distance. Instantly
changing shape, this amazing lens becomes rounder (more highly
curved) for near vision to add more focusing power to your
optical system. Doctors call this process "accommodation".
The crystalline lens of the farsighted eye not only must
become thicker for near vision, but also for distance. In some
hyperopic patients, this elastic lens is unable to compensate
enough to allow clear close vision. If you need correction for
farsightedness, both of your lenses working in concert lack
enough focusing power to "pull" the image forward onto your
retina. Put yet another way, the combined power of your corneal
and crystalline lenses fails to bend light enough to focus it
on your photoreceptors.
If you are farsighted, you may suffer from fatigue or
headaches because of the way your eyes focus. Normally, when
you look at a close object, both eyes naturally move inward
toward each other. The same nerves that control the muscles
that cause your eyes to converge also govern the focusing power
of your crystalline lens. Your adjustable lens and your eye
muscles are designed to work together to provide good single,
binocular near vision. But when a farsighted person looks in
the distance - as each lens adjusts to overcome hyperopia - the
eyes try to turn toward the nose. Since you must look straight
ahead to see far away, your brain instantly counteracts this
automatic response and tells the eye muscles to move your eyes
outward. Such focusing problems can cause eye strain, double
vision, or both.
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