Learning to read is an exceptionally complicated task for visual processing and visual optomotor functions. Children have to recognize letters, chain them into words, chain words into sentences and sentences into paragraphs. In learning to read the eyes must be able to focus (form saccades) letter-by- letter, word-by-word and line-by-line. If an error is made, because word or phrase cannot be recognized in a single gaze, then the person has to backtrack and fix or focus again, in order to re-track the line correctly. Errors may be caused by too long or too short reaction times. If saccades occur too quickly insufficient information may be taken in and letters, words or phrases may be misread or skipped. If there is binocular instability, i.e. if one or both eyes drift from the point of focus In different directions, reading may be both tiring and frustrating.