| Cornea:
The cornea is the eye's primary focusing element and is composed
of transparent, sturdy tissue that allows light to enter the eye
without distortion.
Epithelium:
The epithelium is the cornea's protective outer layer.
Lens:
The lens focuses the light entering through the pupil, directing
it to the retina. The curvature of the lens adjusts to focus at
different distances.
Retina:
Located at the back of the eye, the retina's photosensitive cells
convert light images into electrical impulses for the optic nerve.
The optic nerve sends those impulses to the visual part of the brain.
Refraction:
When the eye's cornea is misshaped and light doesn't focus properly
on the retina, the eye has a refractive problem. There are three
refractive errors: nearsightedness, when you can't see far away;
farsightedness, when you can't see objects up close; and astigmatism,
when you have trouble focusing on any object.
Diopter:
Refractive errors are measured in diopters. Nearsighted people have
negative diopters and farsighted people have positive diopters.
Myopia (Nearsightedness):
Nearsightedness is the most common refractive problem. Nearsighted
people have trouble seeing at a distance and can see near objects
clearly. This occurs when the cornea is too steep and/or the eye
is too long causing light rays to focus in front of the retina.
Distance objects are seen more clearly only with the aid of glasses,
contact lenses or procedures such as laser vision correction.
Hyperopia (Farsightedness):
Farsighted people can't see objects up close. A farsighted eye can
see distant objects more clearly than near objects. This condition
worsens after the age of 40. Farsightedness occurs when the eyeball
is too short, and/or the cornea is flatter than usual. Light rays
don't have enough space or distance to become properly focused before
reaching the retina. Farsightedness can be corrected with glasses,
contact lenses, or procedures such as laser vision correction.
Astigmatism:
Astigmatism is caused by an irregularly shaped cornea that has more
than one curvature (like a football as opposed to a basketball).
These multiple curvatures cause light rays to scatter within the
eye and not to focus on a single point, resulting in blurred vision.
Astigmatism can occur by itself or in conjunction with nearsightedness
or farsightedness. Astigmatism can be corrected with glasses, contact
lenses, or procedures such as laser vision correction.
Presbyopia:
The natural deterioration of near vision caused by loss of flexibility
in the eye's lens as one ages.Presbyopia affects people as they
enter their 40s. Presbyopia affects everyone, and eventually everyone
will need to wear reading glasses or bifocals. Presbyopia is not
affected by the laser treatment.
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