Vision is no doubt, the most important of all our senses. 40% of all the sensory information about our world comes to us through our eyes. But how do we see is one of the oldest scientific questions. The eye is an extraordinary sensitive instrument. The wavelength response to 400-800 nm but its degree of sensitivity is such that a fully dark adopted eye can clearly detect object in light so dim so as to correspond to a light input over the retina of only about 10000 quanta per second.