The Eye: The Physiology of Human Perception by Kara Rogers
Rosen Education Service | 2010 | ISBN: 161530116X, 1615302557 | 250 pages | PDF | 15 MB
Rosen Education Service | 2010 | ISBN: 161530116X, 1615302557 | 250 pages | PDF | 15 MB
The scientifi c study of the eye is believed to have originated with the Greek physician Herophilus, who lived from about 335 to 280 BCE. Indeed, from his work came the words that we use today to describe the various parts of the eye, including the words retina and cornea. In Herophilus’ day, scientists believed that we could see because beams of light came out of our eyes and fi xed on objects. In the centuries since, doctors and anatomists have discovered that vision relies on just the opposite effect. Human eyes are actually light collectors.
Light rays travel from objects around us and stimulate the lightsensitive
cells in our eyes. This book takes a look at these
amazing organs and how they function to allow us to see
the world.
Anyone staring into another person’s eye would notice
that its exterior is mostly white. This part of the human
eye, the sclera, is made up of fi brous tissue and provides a
tough protective coating around the whole eyeball. The
most noticeable part of any eye is the coloured iris and
the dark pupil that it surrounds. The iris, which works
much like the aperture of a camera, expands in darkness to
let more light into the pupil and contracts in bright light
to keep the light-sensitive cells from being overwhelmed.
The colour of the iris comes from melanin, a substance
that protects the eye from absorbing strong light. In the
centre of the iris is the pupil, which allows light and other
visual information into the interior of the eye. The iris and
pupil are protected by a transparent, domelike cover called
the cornea.
Light enters the interior of the eye by passing through
a crystalline lens, which bulges or fl attens, depending on
how far away an image is, and then through a semisolid
gel-fi lled chamber called the vitreous body. The vitreous
body gives the eye shape and fl exibility. Finally, the light
reaches the retina, a membrane made up of
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