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To understand how
these procedures work, you must first understand how your eye
works. The eye functions like a camera. Light rays enter the
eye through the cornea, which provides most of the focusing power.
Light then travels through the lens where it is fine-tuned to
focus properly on the retina. The retina, at the back of the
eye, acts like the film in the camera. Light is changed by the
retina into electrical impulses that are carried by the optic
nerve to the brain. For you to see clearly, light must be focused
precisely on the retina. You need glasses or contacts when your
eyes cannot focus light properly.
ANATOMY
OF THE EYE
Cornea:
The cornea
is sometimes referred to as the window of the eye. It provides
most of the focusing power when light enters your eye. The cornea
is composed of five layers of tissue. The outer layer (the epithelium),
is the eyes protective layer. This layer is
made up of highly regenerative cells that have the ability to
grow back within three day's, and therefore, allow for fast healing
of superficial injuries or surgery.
Pupil: The pupil is the 'black
circle' that you see in people's eyes. The primary function of
the pupil is to control the amount of light entering the eye.
When you are in a bright environment, the pupil becomes smaller
to allow less light through. When it is dark, the pupil expands
to allow more light to reach the back of the eye.
Iris: This is the colored
part you see in people's eyes (i.e. blue/green/brown). The primary
function of the iris is to control the size of the pupil. This
is achieved through contraction or expansion of the muscles of
the iris.
Lens: The lens is the clear structure located
behind the pupil. Its primary function is to provide fine-tuning
for focusing and reading. The lens performs this function
by altering its shape. At about the age of 40-50, the lens becomes
less flexible and presbyopia sets in. At about the age of 60
or 70, the lens becomes cloudy and hard (cataract formation),
preventing light from entering the eye.
VISUAL
REFRACTIVE DISORDERS OF THE EYE
Myopia:
Myopia is the medical term for nearsightedness. Myopia occurs
when an eye is too long for the cornea's curvature. Light rays
entering the eye do not form a sharp focus on the retina at the
back of the eye. Instead, they focus further forward, producing
a blurred image. The term 'nearsighted' means that you can see
'near' objects clearly without your glasses, but objects further
in the distance are blurry. There are varying degrees of myopia
or nearsightedness.
Astigmatism: Many patients with myopia
have some degree of astigmatism, or ovalness to their corneas.
Astigmatism occurs when the cornea is shaped more like a football
than a basketball. As a result, patients with astigmatism experience
distortion or tilting of images because of unequal bending of
light rays entering the eye. Patients with high degrees of astigmatism
have blurred vision not only for distant objects, as with myopia,
but for near objects as well.
Hyperopia: Hyperopia is the medical
term for farsightedness. It occurs when an eye is too short for
the cornea's curvature. Light rays entering the eye focus behind
the retina, and as a result a blurred image is produced. Farsighted
individuals, however, can use their focusing muscles to pull
the image forward onto the retina. When the focusing muscles
weaken with age, presbyopia occurs. In a young person with severe
hyperopia, or once presbyopia sets in, at a later stage, distant
objects are seen more clearly than near objects.
The one advantage to mild myopia is the ability to remove your
glasses after age 40 and continue to read. After any refractive
procedure, you will lose this ability. You will typically be
normally sighted after the procedure, and you will need reading
gasses for small print, like every other normally sighted person
at the age of 40-50. |
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