Lens
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| 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.
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| 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
Cassel, G. Billig. The Eye Book: A Complete Guide to Eye Disorders and Health.
Baltimore, MA: Johns Hopkins University Press, 1988.
Collins, J.F. Your Eyes: An Owner's Guide. Englewood Cliffs, NJ: Prentice
Hall, 1995.
D'Alonzo, T.L. Your Eyes: A Comprehensive Look at the Understanding and
Treatment of Vision Problems. Clifton Heights, PA: Avanti Publishing, 1991.
Eden, J. The Physician's Guide to Cataracts, Glaucoma, and Other Eye Problems.
New York, NY: Consumer Reports Books, A Division of Consumers Union Yonkers,
1992.
Schuman, B.N. The Human Eye. New York, NY: Atheneum, 1986.
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, Canada: Collier Macmillan Canada, 1997.
Kwiko, M.L. Eyes. Toronto, Canada: Key Porter Books, 1994.
Rainwater, J. Vision: How, Why, and What We See. New York, NY: Golden
Press, 1992.
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