ÃÂÃ ÃÂÃ ÃÂÃ ÃÂÃ ÃÂÃ ÃÂÃ ÃÂÃ ÃÂÃ The human eye does alot more than allowing you to
see. It is very complex and has many parts and features
which can have defects. However, to understand defects
you must first know how the eye works.
ÃÂÃ ÃÂÃ ÃÂÃ ÃÂÃ ÃÂÃ ÃÂÃ ÃÂÃ ÃÂÃ First light passes through the cornea, which is the
transparent part of the sclera, or white of the eye, which is
composed of tough fiberous tissue. Behind the sclera is a
watery fluid called the aqueous humor. This fluid fills a
cresent-shaped space which with the cornea helps bend
the light toward the center of the eye.
ÃÂÃ ÃÂÃ ÃÂÃ ÃÂÃ ÃÂÃ ÃÂÃ ÃÂÃ ÃÂÃ Under the aqueous humor is the iris which gives the
eye color. The color of the iris has no effect on how you
see and is inherited through genes. The iris contols how
much light is allowed to enter your by opening up
further when it is dark and closing up more to block out
some light when it is bright.
Everything that passes
through the pupil, which looks like a black dot, is what
you see.
ÃÂÃ ÃÂÃ ÃÂÃ ÃÂÃ ÃÂÃ ÃÂÃ ÃÂÃ ÃÂÃ Next the light passes through the lens. The lens
focuses the light rays onto the retina forming an image
in reverse and upside-down. Finally light-sensitive
cells in the retina transmit the image via the optic nerve
to the brain by electrical signals. Then the brain flips
the image so it looks right-side-up to you. You can find
a diagram of the above on page 3.
page 1
ÃÂÃ ÃÂÃ ÃÂÃ ÃÂÃ ÃÂÃ ÃÂÃ ÃÂÃ ÃÂÃ The most common visual defects are nearsightedness
and farsightedness. In nearsightedness, also known as
myopia, the eye is longer than usual. This is corrected by
using a concave lens to spread the light rays just enough to
increase the eye's focal length. Hyperopia, also known as
farsightedness, is caused by a shorter than usual eye. A
convex lens increases light bending and...