rocess of vision Light waves from an object (such as a tree) enter the eye first through the cornea, which is the clear dome at the front of the eye. It is like a window that allows light to enter the eye. The light then progresses through the pupil, the circular opening in the center of the colored iris. Fluctuations in the intensity of incoming light change the size of the eye’s pupil. As the light entering the eye becomes brighter, the pupil will constrict (get smaller), due to the pupillary light response. As the entering light becomes dimmer, the pupil will dilate (get larger). Initially, the light waves are bent or converged first by the cornea, and then further by the crystalline lens (located immediately behind the iris and the pupil), to a nodal point (N) located immediately behind the back surface of the lens. At that point, the image becomes reversed (turned backwards) and inverted (turned upside-down). The light continues through the vitreous humor, the clear gel that makes up about 80% of the eye’s volume, and then, ideally, back to a clear focus on the retina, behind the vitreous. The small central area of the retina is the macula, which provides the best vision of any location in the retina. If the eye is considered to be a type of camera (albeit, an extremely complex one), the retina is equivalent to the film inside of the camera, registering the tiny photons of light interacting with it. Within the layers of the retina, light impulses are changed into electrical signals. Then they are sent through the optic nerve, along the visual pathway, to the occipital cortex at the posterior (back) of the brain. Here, the electrical signals are interpreted or “seen” by the brain as a visual image. Actually, then, we do not “see” with our eyes but, rather, with our brains. Our eyes merely are the beginning of the visual process. Watch an 11½-minute film, created in 1941, about the anatomy and physiology of the eye: How the Eye Functions.
Posted on: Mon, 01 Jul 2013 05:58:25 +0000
Trending Topics
Recently Viewed Topics
© 2015