Vision occurs when light reflected from an object travels through the eye and is interpreted by the brain. 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 just behind the cornea which controls the amount of light entering the eye through the pupil. The lens inside the eye fine tunes the focusing 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.
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What is 20/20 vision?
20/20 vision means that vision is normal at a distance of 20 feet. If the patient can only see at a distance of 20 feet what the average person can see at 40 feet, he has 20/40 vision. If the patient 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.
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 a correction is necessary, but also to monitor the health of the eye. With early detection and treatment, vision loss from many diseases can be prevented.
If you are experiencing a vision problem, you should obtain a complete eye examination.