ABSTRACT
The detection of an image in the visual field is primarily dependent upon two sets of factors: the optical system of the eye, and the receptor system of the retina. These have been likened to the lens and the photographic film of a camera. The lens has to focus the image on the retina, the image being reversed laterally and inverted. The convex lens can be changed in shape, so that objects at different distances can be brought into focus.
