Light And dArk AdAptAtion
• Light adaptation is the ability of the eye to quickly
adjust when we move from the dark into the bright
light.
• Initially, the eye is extremely sensitive to light as rods
are overwhelmingly activated. resultant image is too
bright with poor contrast.
• The rhodopsin is soon inactivated (bleached) by the
bright light and scotopsin is formed making rods
unresponsive, so that only less-sensitive cones are
working, and the image becomes better.
• Dark adaptation is the ability of the eye to recover its
sensitivity in the dark following exposure to bright light.
• Initially we see only blackness, because the cones stop
functioning in low intensity light. Dark adaptation
occurs when enzymes regenerate the non-active form
of rhodopsin, which can respond to low levels of light.
• complete adaptation is accompanied by changes in
pupil size also.
typEs oF Vision
Binocular or monocular vision
• human beings have binocular and stereoscopic
(3-dimensional) vision.
• For this, both the eyeballs have to be moved to focus
on the same object, by means of external muscles. The
phenomenon is called convergence. It gives clearer
image with better idea of distance.