How the eye works

The Eye


It passes through the pupil, the adjustable opening where light enters. The amount of light that enters is regulated by the iris, a ring of muscle tissue that forms the colored portion of the eye.
Behind the pupil is a lens that changes shape to focus images. The process which the eye's lens changes shape to focus is called accommodation. The light-sensitive inner surface of the eye is the retina.

external image humanvisionfigure1.jpg
Acuity, the sharpness of vision, can be affected by small distortions in the eye's shape. In nearsightedness, nearby objects are seen more clearly than distant objects because distant objects focus in front of retina.

external image humanvisionfigure8.jpg
Farsightedness is the opposite of nearsightedness.
A single particle of light energy in your eye first makes its way through the retina's outer layer to its buried receptor cells, the rods and cones. An optic nerve carries neural impulses from the eye to the brain. The point at which the optic nerve leaves the eye, creating a "blind" spot because there are no receptor cells located there.


external image humanvisionfigure5.jpg
Cones cluster around the fovea, the central focal point in the retina.

References


Myers, D. G. (2007). Psychology (8th ed., pp. 205-208). New York: Worth.
Spring, K. R., Davidson, M. W., & Fellers, T. J. (1998, June 1). Human Vision and Color Perception. Retrieved January 4, 2009, from http://micro.magnet.fsu.edu/primer/lightandcolor/humanvisionintro.html
RECEPTORS IN THE HUMAN EYE
Cones
Rods
Number
6 million
120 million
Location in retina
Center
Periphery
Sensitivity in dim light
Low
High
Color sensitive?
Yes
No
Detail sensitive?
Yes
No