 |
| Light rays bend once more as they pass
through the lens. |
The iris and pupil allow light to pass through the
cornea and into the lens. The lens is like a transparent
seed, having curved surfaces at the front and back. This
bends light twice as it passes through. The lens does
about 25 percent of the focusing work.
 |
| The ciliary muscles contract and expand,
changing the shape of the lens to improve focus. |
Unlike the cornea, the shape of the lens is
adjustable, which improves refraction. The lens is made
of highly elastic fibers. The ciliary body, a tiny
muscle group connected to the lens by fibers called
zonules, adjusts the len's thickness. The ciliary body
squeezes the lens to make it thicker for focusing on
near objects, and flattens it to view distant objects.
The lens is bathed, nourished and cushioned by the
aqueous humor, which flows from the iris.
Sources
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Understanding and Treatment of Vision Problems.
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Eden, J. The Physician's Guide to Cataracts,
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Consumer Reports Books, A Division of Consumers Union
Yonkers, 1992.
Schuman, B.N. The Human Eye. New York, NY:
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Adler, R., Adler, I. Your Eyes. New York, NY: The
John Day Company, 1992.
Begbie, G.H. Seeing and the Eye: an Introduction to
Vision. Garden City, NY: National History Press,
1996.
Cohen, N.S. Out of Sight Into Vision: There is More
to Good Vision Than Reading the Fine Print. Toronto,
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Kwiko, M.L. Eyes. Toronto, Canada: Key Porter
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Rainwater, J. Vision: How, Why, and What We See.
New York, NY: Golden Press, 1992. |
