Unlike "eyesight" which describes only visual acuity, "vision" describes the combination of three sequential processes: (1) light clearly focusing on the retina of each eye which (2) the brain then combines into a single image for (3) visual information processing. Step 1 is corrected with eyeglasses and step 3 with a host of therapeutic disciplines. "Vision skills" are all about step two – which requires the image from each eye to stay in focus while the eyes are in coordinated motion (at the plane of a page, as in reading). Otherwise, the visual information is not primed for processing.

The eye muscles necessary to accomplish step 2 can be uncoordinated as a product of stress or injury or have underdeveloped range of motion and therefore affect "vision". Like any other muscles over which we have conscious control, they can respond to proper incremental exercise and training to increase capacity, range of motion and perceptual integration. In the case of injury, compensatory strategies may also be employed.

The classic model of an eye is one of a camera, with the iris as the camera shutter, the cornea and intraocular lens as the camera lenses and the retina as the "film". But when describing how two eyes work everyone references "binocular vision", so let's use a pair of binoculars as a model of vision:



In the context of learning, abnormal facility in tracking, focusing or eye teaming can create a distraction from schoolwork leading to a learning disability created by the effort required to sustain single and/or clear images. While some highly motivated individuals find compensatory ways to maintain acceptable schoolwork, most will acquire poor work habits, avoid schoolwork and/or behave poorly.

Since many individuals with abnormal vision skills can force themselves to see clearly or singly for the moment their "vision" is screened, they often pass and go undetected. When considered for special services or occupational therapy, an underachieving student or young adult with a vision skills deficiency may have been certified "visually O.K." by routine screening when indeed they are not. This issue may be compounded when a near visual acuity test is employed. Just because a subject can read small print up close for a moment does not mean that they can easily sustain that or other close tasks.