The Human eye

Click for Full Size The eye Credits: Franklin Branley, Henry Roth

            The eye is a complicated organ which allows us to see.  To understand it, we must first look at the biology of the eye.  The pupil is an opening which allows Light to pass into the eye.  It is the dark hole in the center of your eye.  The pupil is controlled by the iris (the colored part of the eye) which is a muscle that contracts to make the pupil smaller and relaxes to allow the pupil to widen.  The pupil’s size relates to how much Light there is in a particular setting.  If you are standing outside and the sun is really bright, then your pupil will get smaller to make up for this.  The iris is covered by the cornea.  The lens of the eye is located in back of the iris.  The lens focuses the Light onto the retina, which acts like a screen.  eyelashes and eyelids protect the eye by stopping dust particles from falling onto the eye itself.  The purpose of blinking is to moisten the cornea.  If the cornea were not kept wet, it would become opaque.

            There are two types of Light sensitive cells on the retina.  Rods, are used for black and white vision, and are concentrated on the sides of the retina.  Cones are used for color vision, and are concentrated in the center of the retina.  Vision is most acute in the area of the retina known as the fovea centralis.