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The eye is a complex optical system - very similar to a camera. Vision
begins when light enters the eye through the cornea, a powerful focusing
surface. From there, it travels through clear aqueous fluid, and passes
through a small aperture called the pupil. As muscles in the iris relax or
constrict, the pupil changes size to adjust the amount of light entering the
eye. Light rays are focused through the
lens, and proceed through a clear jelly-like substance in the center of
the eye called vitreous, which gives it form and shape. When light rays
finally land on the retina, the part of the eye similar to film in a camera,
they form an upside-down image. The retina converts the image into an
electrical impulse that travels along the optic nerve to the brain, where it
is interpreted as an upright image.
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