How
the Eyes Work
Some
people liken the eye to a camera. As light passes through the
lens it is bent and transposed onto the eye's film - the retina.
The film is then 'developed' by the brain, becoming the image
that we see.
As light enters the eye it first passes through the cornea -
the clear 'window' to the eye. Because the cornea is curved,
the light rays bend (refract). Light then passes through the
pupil to the lens. The iris - the colored portion of the eye
- controls the amount of light that enters the eye with muscles
that cause the pupil to contract if there is too much light
or to dilate if there is too little light. When light hits the
curved surface of the lens it is refracted, or bent even more,
so that it focuses properly on the retina. The retina then turns
the light into electrical energy, which passes through the optic
nerve to the brain stem, and into the occipital lobe where it
is converted into an image. To summarize:
· Cornea - clear surface of the eye. Light rays
refract as they pass through to the pupil.
· Iris - colored portion of the eye. The iris
controls the amount of light that passes through
the pupil.
· Pupil - an open space in the center of the iris.
Light passes through the pupil to the lens.
· Lens - refracts light to focus it properly on
the retina.
· Retina - converts light rays into electrical
energy. This electrical energy is passed to the
optic nerve.
· Optic Nerve - serves as a pathway to the brain
stem, which forwards electrical energy to the occipital
lobe.
· Occipital Lobe - electrical energy is converted
into an image.
This process works perfectly in people with 20/20 vision. Imperfect
vision occurs when the shape of the eye is irregular or when
the light rays do not focus directly on the retina - these imperfections
are collectively known as refractive errors.
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