Some General Aspects of Vision

Abstract

The mechanism by which the energy contained in visible light is transmitted to the nervous tissue of the retina in such a way as to produce that change in its structure which we call a stimulus is a fascinating problem and one that lends itself to physicochemical study. There is a group of chemical reactions that derive a part, or all, of their energy from absorbed light—the photochemical reactions—a biological instance of this type of reaction is the synthesis of carbohydrate by the green leaves of plants, the pigment chlorophyll absorbing light and transmitting the energy to the chemical reactants. It is thus reasonable to inquire whether there is an analogous chemical reaction at the basis of the response of the retina to light, i.e. whether or not there are substances in the retina that can absorb visible light and, as a consequence of this absorption of energy, can modify the fundamental structure of the rod or cone to initiate a propagated impulse.