Accommodation (eye focusing): The ability to focus the eyes to see clearly up close, to change focus from distance to near and back again, and to maintain clear focus for an extended period of time. Poor eye focusing ability can make it difficult to concentrate on reading from a book for a long period of time.
Amblyopia (lazy eye): Reduced vision in an eye, not correctable with eye glasses, as a result of the eye not receiving adequate use during early childhood. Most often it results from either misalignment of a child’s eyes or a large difference in image quality seen with the two eyes. Over time the eye with the least clear image is ignored or suppressed making 3D/stereo vision impossible.
Binocular vision (eye coordination): The ability of both eyes to work together as a team. Each eye sees a slightly different image and the brain, by a process called fusion, blends the images into one three dimensional picture. Good eye coordination, a skill that must be developed, keeps the eyes in alignment. Poor eye coordination comes from a lack of adequate vision development or improperly developed control of eye muscles.
Convergence insufficiency: a form of a binocular vision problem where the two eyes don’t turn in correctly. When we read our eyes have to turn in and they have to point to the same place on the page. If one eye doesn’t line up with the other it can cause problems with reading, such as loss of place, loss of concentration, reading slowly, eyestrain, headaches, blurry vision and double vision.
Ocular motility (eye tracking): The ability to smoothly and accurately move the eyes along a line of print or follow a moving target with our eyes. Poor eye tracking can result in skipping words, losing one’s place on a page, having to re-read materials, or difficulty copying from the chalkboard.
Strabismus (crossed eyes): An inability of the two eyes to aim at the same place at the same time. This can result in an eye turning in, out, up or down. A child with crossed eyes may experience periods of double vision and if untreated this condition can lead to amblyopia.
Visual-motor integration (eye-hand-body coordination): The ability to integrate visual information with gross and fine motor movements. Inadequate visual motor integration can result in clumsiness and difficulty with handwriting.
Visual perception (visual information processing): The process by which the brain interprets and understands the visual information received by the eyes. Aspects of visual perception include visual memory, size and form perception, directionality and color perception. Poor visual perception may contribute to letter reversals or difficulty with comprehension when reading.
For more information: www.covd.org