The Able Eye
Below are visual skills, abilities, and terms that contribute to healthy vision.
Accommodation is the ability to adjust the focus of the eyes as the distance between the individual and the object changes. Children frequently use this vision skill in the classroom as they shift their attention and focus between their book and the chalkboard for sustained periods of time. Being able to maintain focus up close for these uninterrupted periods of time is important for reading, writing and also taking tests (see: accommodative dysfunction).
Binocular Fusion or Binocularity refers to the brain's ability to gather information received from each eye separately and form a single, unified image. A child's eyes must be precisely aligned, otherwise blurred or double vision, discomfort, confusion or avoidance may result. If this occurs, the brain often subconsciously suppresses or inhibits the vision in one eye to avoid confusion. That eye may then develop poorer visual acuity (see: amblyopia or lazy eye).
Convergence is the ability to turn both eyes toward each other to look at a close object. School deskwork, such as reading, is one instance in which a child depends on this vision skill.
Field of Vision is the wide area over which vision is possible. It is important that a child be aware of objects in the periphery (left and right sides and up and down) as well as in the center of the field of vision. Near central or Para-central vision is important for reading ability.
Perception can be broken down into visual and form perception. Visual perception is the total process responsible for the reception and understanding of what is seen. Good visual perception is necessary for successful school achievement. Form perception is the ability to organize and recognize visual images as specific shapes. The shapes a child encounters are remembered, defined and recalled when reading skill development begins.
Visual Acuity is sharpness or clearness of vision and the ability of eyes to see fine detail. Determined by how effectively light is focused in each eye, testing distance visual acuity is a common measure of eyesight, and involves reading letters on an eye chart across a room. A reduced eye chart can also be used to measure near visual acuity at normal reading distances. The level of visual acuity is written as a fraction such as 20/40. The top number in the fraction is the standard distance at which testing is done, twenty feet. The bottom number is the smallest letter size the child was able to read. Normal distance visual acuity is 20/20. A child with 20/40 visual acuity would have to get within 20 feet of a letter that should be seen as far away as 40 feet in order to see it clearly. If a child has less than 20/20 visual acuity, he or she may have difficulty copying from the chalkboard or watching a movie in class.
Visual Fixation is the skill utilized to aim the eyes accurately. Static fixation is the ability to focus on a stationary object when reading a word or working a math problem. Saccadic fixation is the ability to move the eyes quickly and accurately across a page to read a line of print. Pursuit fixation is the ability to follow a moving object with the eyes. These complex operations require split second timing for the brain to process the information received and to track the path of the moving object (see: ocular motor dysfunction).