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The human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the mammalian eye allows vision. Rod and cone cells in theretina allow conscious light perception and vision including color differentiation and the perception of depth. The human eye can distinguish about 10 million colors.

In common with the eyes of other mammals, the human eye’s non-image-formingphotosensitive ganglion cells in the retina receive the light signals which affect adjustment of the size of the pupil, regulation and suppression of the hormonemelatonin and entrainment of the body clock.

Source: Wikipedia