The Physics Factbook
Edited by Glenn Elert -- Written by his students
An educational, Fair Use website
|Glencoe Health 2nd Edition. Mission Hills: Glencoe Inc., 1989: 61.||"The eyeball is about 1 inch (2.5 cm) in diameter"||25 mm|
|Encyclopedia Britannica Macropedia: Sensory Reception. USA: Britannica Inc., 1997.||"The dimensions of the eye are reasonably constant, varying among individuals by only a millimetre or two; the sagittal (vertical) diameter is about 24 millimetres (about one inch) and is usually less than the transverse diameter."||24 mm|
|Magill's Medical Guide Revised Edition; Brain. Salem Press, 1998: 608.||"The adult human eye weighs approximately 7.5 grams and measures approximately 24.5 millimeters in its anterior-to-posterior diameter."||24.5 mm|
|Zinn, Walter and Solomon, Herbert. Eye Care, Eye Glasses and Contact Lenses. City: Lifetime Books, 1965: 10.||"The eyeball is roughly about an inch in diameter brimming with many specialized structures and tissues."||25 mm|
|World Book 2001. Chicago: World Book Inc., 2001: Page 460.||"The human eyeball measures only about 1 inch"||25 mm|
The human eye is the organ of sight. We use our eyes for reading, working, watching television and many other activities.
The eye doesn't actually see objects. Instead, it receives light reflected from the objects. Light rays enter the eye through transparent tissues. The eye changes the rays into electrical signals. The signals are then sent to the brain, which interprets them as visual images.
Eye formation begins during the end of the third week of development when outgrowths of brain neural tissue, called the optic vesicles, form at the sides of the forebrain region. The major structures of the eye- the retina, lens, and eyeball coats- are initially formed by the fifth month of fetal development. During the remainder of the prenatal period, eye structures continue to enlarge, mature and form increasingly complex neural networks with the visual processing regions of the brain.
At birth, an infants eyes are about two-thirds the size of adult eyes. Until after their first month of life, most newborns lack complete retinal development, especially in the area responsible for visual acuity. From the second year of life until puberty, eye growth progressively slows. After puberty, eye growth is negligible.
Anicia Ndabahaliye -- 2002
Author, Illustrator, Webmaster
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