The retina is a membrane that lines the rear of the globe and converts visual signals into electrical impulses. In our camera analogy, the retina is the film of the camera. The cornea and the lens bring light into sharp focus on the macula, a specific region of the retina.
Rod and cone cells, photoreceptor cells on the retina, sense actual photons (particles of light) and differentiate their frequencies, which we interpret as the various colors. This information travels along the optic nerve to the brain’s visual cortex. We have a limited knowledge of how visual signals are processed at present and, in particular, of how the brain copes with the limited “channel capacity” of the optic nerve. Research to provide a more thorough understanding of how our minds produce a detailed, continuous image is ongoing.
Six orbital muscles outside of the eye control movement. Four are responsible for movement up, down and sideways, and the other two keep the eyes aligned as the head moves. The eyelids, the thin folds of skin which cover and protect the eyes from debris and perspiration, are also responsible for spreading secretions on the eye and for the tear film that lubricates the cornea, which must always be kept moist.