We want you to learn more about your eyes so you will take good care of them. Please take time to view the anatomical aspects of the eye and begin to understand how your eye health relates to your everyday vision.

The Anatomy of an Eye
Thanks to Dr. Ted Montgomery for providing us with the following overview of the eye and how it works.

The human eye is the organ that gives us the sense of sight, allowing us to learn more about the surrounding world than we do with any of the other four senses. We use our eyes in almost every activity we perform, whether reading, working, watching television, writing a letter, driving a car, and in countless other ways. Probably most people would agree that sight is the most precious of the five senses, and many people fear blindness more than any other disability.

The eye allows us to see and interpret the shapes, colors, and dimensions of objects in the world by processing the light they reflect or give off. The eye is able to see in dim light or bright light, but it cannot see objects when light is absent.

Light from an object (such as a tree) enters the eye first through the clear cornea and then through the pupil, the circular opening in the iris. Next, the light is converged by the crystalline lens to a point immediately behind the lens; at that point, the image becomes inverted. The light progresses through the gelatinous vitreous humor and, ideally, back to a clear focus on the retina, the central area of which is the macula. In the retina, light impulses are changed into electrical signals and then sent along the optic nerve and back to the occipital (posterior) lobe of the brain, which interprets these electrical signals as visual images.

If the incoming light from a far away object focuses before it gets to the back of the eye, that eye?s refractive error is called "myopia" (nearsightedness). If incoming light has not focused by the time it reaches the back of the eye, that eye?s refractive error is "hyperopia" (farsightedness).

In the case of "astigmatism," one or more surfaces of the cornea or lens (the eye structures which focus incoming light) are not spherical (shaped like the side of a basketball) but, rather, are cylindrical (shaped like the side of a football). As a result, there is no distinct point of focus inside the eye but, rather, a smeared or spread-out focus. Astigmatism is the most common refractive error.

After age 40, and most noticeably after 45, the human eye is affected by "presbyopia," which results in greater difficulty maintaining a clear focus at a near distance with an eye which sees clearly at a far away distance. This is due to a lessening of flexibility of the crystalline lens, as well as to a weakening of the ciliary muscles which control lens focusing, both attributable to the aging process.

The average eyeball measures approximately 24-25 millimeters, or about 1 inch, in diameter. (A ping-pong ball is about 1 1/2 inch in diameter, which makes the average eyeball about 2/3 the size of a ping-pong ball.) The eyeball is set in a protective cone-shaped cavity in the skull called the "orbit" or "socket." The orbit is surrounded by layers of soft, fatty tissue which protect the eye and enable it to turn easily. Three pairs of extraocular muscles regulate the motion of each eye: the medial/external rectus muscles, the superior/inferior rectus muscles, and the superior/inferior oblique muscles.

View an animated illustration of how the eye works.
View this excellent interactive exploration of the eye provided to us by The Sight and Hearing Association.