The gift of sight is one of our most important senses. Without good vision, many daily activities, such as reading and driving, would be difficult. With a good understanding of how the eye works and the importance of total eye care, healthy eyes and good vision can be maintained.

How Does the Eye Work?

Vision occurs when light reflected from an object travels through the center of the eye and is interpreted by the brain. The eye is made up of many different parts which work together to provide sight.

Light enters the eye through the cornea, the clear covering of the eye. The cornea is partially responsible for focusing the light images which enter the eye. The iris, or colored portion of the eye, is a muscle located behind the cornea and controls the amount of light entering the eye via the pupil. The lens inside the eye fine tunes the focus of the image by changing shape, depending on whether the object is close-up or far away.

After passing through the lens, light rays are focused onto the retina at the back of the eye. The retina consists of light sensitive nerve tissue called rods and cones. The rods function best in dim light, while the cones function best in daylight conditions, and also perceive color. The rods and cones transform the light images into electrical impulses which are sent to the brain by the optic nerve. When the brain interprets the image, vision occurs.

What is 20/20 Vision?

20/20 vision means that vision is normal at a distance of 20 feet. If a person can only see at a distance of 20 feet what the average person can see at 40 feet, he has 20/40 vision. If a person can see at 20 feet what the normal person can see at a distance of 15 feet, he has 20/15 vision or better than average vision. While these figures measure the ability to see straight ahead it is also necessary to have good peripheral (side) vision, eye coordination, depth perception, color vision, and night vision.

What is a Refractive Error?

Many common vision problems are caused by refractive errors. This is an irregularity in the way light passes through the eye. Normally, light enters the eye and is focused at a single point on the retina. With a refractive error, light rays do not refract or bend properly to achieve a single focus point on the retina. Instead, light rays either focus in front of the retina, behind the retina, or do not focus at a single point. Refractive errors such as nearsightedness, farsightedness, astigmatism, and presbyopia usually result from a problem with the shape of the eye, cornea or lens.

Prevention is the Best Medicine

Regular eye examinations are an important part of total eye care. Eye exams are necessary not only to measure vision and determine if any correction is necessary but also to monitor the health of the eye. With early detection and treatment, vision loss from many eye diseases can be prevented.