How do the
Your eyes are like a camera. They take pictures of
the world around you and send the pictures to your brain. Your brain
interprets what you are seeing. This process begins from the moment you
open your eyes in the morning until you close them for bed at night.
Only part of the eye is visible in a person’s face.
The whole eye, the eyeball, is about the size of a ping pong ball. The
eyeball is made up of different parts that all have an important job:
the cornea, helps the eye to focus; the iris, the colored part; the
pupil, lets light into the eye; and the retina, found at the very back
of the eye.
When light passes through the cornea, the light
gets bent so the image can be focused sharply on the retina. The better
“picture” the retina takes, the more likely you will see the image
clearly. The retina can take a color picture because the retina is made
up of two types of light collectors, called rods and cones. The rods are
used to discern black and white, and the cones are for color. The cones
can be divided into red cones, green cones, and blue cones. These
account for the variation of color that humans can see.
Why do some
people need glasses?
Refracting means bending light rays. If a person
has vision trouble, it is often a refraction problem. Glasses or contact
lenses help correct the problems with light bending. The most common
refraction problems are nearsightedness and farsightedness. Nearsighted
means a person can see things that are near, but not far. Farsighted
means the person can see things that are far away, but not close. In
both, the image is not properly focused on the retina. With
nearsightedness, the image is too close to the front of the retina, and
in farsightedness, the image is focused behind the retina.
Another refraction problem is astigmatism (uh-stig-muh-tih-zum).
This means that the cornea is an uneven shape, and it bends the light in
many different directions instead of one. This can cause the images a
person sees to be blurry.
Glasses and contact lenses correct vision, because
they move where the light bends to shine on the correct part of the
retina, the spot that creates the clearest image. Everyone’s eyes are
different, and if a person needs glasses, the glasses are designed
specifically for their eyes.
A vision prescription has the numbers the
manufacturer needs to create the lenses that bend the light to hit the
middle of your retina. With these lenses, most vision problems are
corrected and the person can see clearly.