by Michelle Mock
Peter, age 7, has just been given a vision screening at school. No problems have been found and his parents are told that he has 20/20 vision. "You have perfect eyesight!" they tell Peter.
Good eyesight according to the Snellen test (the screening given at most schools) is only a small part of vision health or wellness. This test measures visual acuity only. While Peter may be able to read the proper line of the eye chart from a distance of twenty feet, he may have other vision problems.
Vision is a learned skill similar to walking and talking. When a baby learns to walk or talk, he experiments with different muscle groups until he achieves the desired result (i.e., he makes a sound or takes a step). Vision is acquired in the same manner, but the muscle movements are mostly involuntary.
The baby learns to move the muscles associated with the eyes. When he relaxes the focusing muscle, the eye can see distant objects clearly. Tightening the muscle causes near objects to come into focus. The baby does not have to think about these movements, they just happen. The baby learns to focus.
Moving the eyes the baby is able to track a moving object. He turns his head to see objects on his left or right. These movements are conscious movements. As the baby learns to use his eyes, his vision improves.
Vision health, or wellness, is the ability to use the eyes effectively to gather information. Vision wellness is not simply the ability to see.
When a baby is learning to walk and talk, he gets feedback from the people around him. When he is acquiring his vision skills, most of the feedback he gets is internal. He interprets what he sees and he develops his skills in response to his own interpretation. Errors in this interpretation are often not noticed until the child reaches elementary school. By that time, vision problems are usually masked by behavior and other learning difficulties.
Vision therapy can correct many of the problems associated with how the eyes work. By exercising the appropriate muscles and training the patient to be aware of how those muscles feel, vision therapy can greatly improve the functioning of the visual system. The intent of vision therapy is not to strengthen the muscles but to coordinate the vision process to make it more effective.
If Peter is having difficulty in school, he could be demonstrating deficiencies in his visual system. For example, reading requires the effective use of eight different skills: visual acuity, visual fixation and tracking, accomodation, binocular fusion, convergence, stereopsis, field of vision and form perception. (American Optometric Association)
Peter is demonstrating an inability to read at grade level, his attention is poor, and he is easily distracted. Peter's teacher notices that he tilts his head or closes one eye when he reads. He sometimes rests his cheek on his arm as he writes or he turns his paper in an awkward direction.
He is referred to an optometrist who asks Peter to follow the movement of a small dinosaur on the end of a pencil. The doctor notices that Peter's eyes jerk and his head moves as he follows the movement of the dinosaur. The optometrist notes a tracking problem.
Peter is then asked stand about ten feet from a wall chart. In his hand he holds a smaller version of the chart. He is asked to alternately read a letter off the wall chart and then off the card he holds in his hand. As he alternates between near and far, his eyes begin to water and he loses his place. The optometrist notes an accomodation problem.
The optometrist continues his exam and also notes that Peter is slightly farsighted as well. Some vision problems such as farsightedness (hyperopia) can be corrected or improved through the use of prescription lenses. The other vision problems can be corrected or improved through vision therapy.
In Peter's case, a combination of corrective lenses and vision therapy can work together to improve his vision and subsequently his school work.
The American Optometric Association has verified the benefits of vision therapy. While therapy cannot benefit everyone, Peter's problems and many other vision problems can be significantly reduced through the conscientious use of therapy.
- 26 April 1994
Visual Acuity is the ability to see objects clearly. Peter should be able to comfortably see near objects (13-16 inches) or distant objects (10 feet or more).
Visual Fixation is the ability to aim the eyes accurately. Peter should be able to focus on a stationary object or line of print. He should also be able to follow a moving object with his eyes.
Accomodation is the ability to adjust the focus of the eyes between near and far objects.
Binocular Fusion is the ability to use two eyes together to form a single image in the brain. If the information is not fused into one image, the brain may suppress the information from one eye.
Convergence is the ability to turn the eyes inward to see near objects. Divergence is the ability to move the eyes out to see the bigger picture.
Stereopsis is the ability to judge the relative distance between objects. Eye/hand coordination is affected by stereopsis.
Field of Vision is the ability to see or be aware of peripheral objects (to the left, right, up and down) as well as the center of the field of vision.
Perception is the reception and interpretation of the visual stimuli.
13 March 2002
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