The Human Visual System

The human visual system receives and processes electromagnetic energy in the form of light waves. The photopigments in receptors in the retina of the eye transform this light energy into electrical energy/impulses sent to the vision center within the brain. It is estimated that vision accounts for at least 40% of brain functioning. The human visual system is highly complex and is not yet fully understood. In speed, efficacy, and power, it has yet to be equaled by any human-developed system.

The way a camera functions is roughly analogous to the human eye. In the eye, focusing is performed by the cornea and lens. The iris adjusts the pupil or aperture to accommodate the amount of light in the environment by making the pupil larger in low light and smaller in bright light. The retina, that lines the eye with receptor cells containing photosensitive pigments, resembles film--except we do not "see" a one-to-one representation of the retinal image. Image processing begins in the retina and is completed in the brain, creating our "perception" of the world.

The cornea and lens focus light waves on the fovea, at the back of the retina, where our visual acuity is greatest because of the high concentration of receptor cells.

(Image adapted from a National Eye Institute, National Institutes of Health (NIH) graphic.)