ABSTRACT
Vision is a very complicated process dependent on the transparent media of the eye asthecornea,thelens,andthevitreoushumor,providingaclearimageontheretina. Thechangeintheshapeofthelensintheaccommodationprocessassuresclear imagesatdifferentdistances.The120millionrodsand6millionconesofthehuman retinatogetherwiththreelayersofnucleiperformbillionsofcalculationspersecond before the signal reaches the optic nerve. Then the cerebral cortex processes the informationinthevisioncenters.Thethreedifferentpigmentsintheretinalcones constitutethemainsourceofcolorvision.Theeyeadaptstolightanddarkoveran intensityrangeof1-100,000(Newell,1992).Thelocationofhumaneyeballsinthe orbitsinfrontoftheheadandthedecussationofaxonsfromnasalpartofeachretina permit a retinal correspondence and stereoscopic vision. The vision process requires energy to provide its metabolic needs by several metabolic pathways.
