The eye functions like a
camera. Light rays enter the eye through the cornea (the
clear front window), pass through the pupil (the hole in the
center of the iris), and then through the lens, finally
reaching the retina (the film) at the back of the eye. When
light rays land on the retina, they form an upside-down
image. The retina converts the image into impulses that
travel through the optic nerve to the brain, which converts
them into upright visual images.
Vision is clear only if the
cornea and lens correctly bend or "refract" the light rays
and focus them on the retina. Blurry vision may be due to
what is called a "refractive error" --- the failure of the
cornea and lens to focus light properly. Prescription eye
glasses, contact lenses, and refractive surgery correct or
improve refractive errors by focusing light rays closer to,
or directly onto, the retina.
More than 90 percent of our
knowledge is obtained through our eyes making vision the
most valued of the five senses. However, millions of people
suffer from diseases, disorders or injuries to the eye.