Lens therapy for young readers with accommodative-vergence deficits.

The experiments described in this thesis represent an evaluation of the effects of nearpoint lens wear in children with accommodative-vergence deficits. Firstly, the effects of reading on pulse rate in ten children with accommodative-vergence deficits were examined, in order to determine whether or not reading is in fact a "stressful" activity. No significant change in pulse rate was demonstrated during the reading of two short narrative passages. Next, afocal magnifying or "size" lenses were used to determine whether reading performance improves in nearpoint lens wearers because of a placebomediated association between large print and simple, easily read text. Only one third of the participants in this experiment were able to correctly identify differences in image size of similar magnitude to the magnification produced by common nearpoint prescriptions. A group of three experiments then examined the effects of nearpoint lens wear on reading performance and on visual skills, and the relationships between "visual efficiency" and reading performance. Afocal size lenses were used as the control condition, yet both lens wear conditions were associated with changes in reading performance and visual skills. These experiments offer limited support for nearpoint stress theories. Finally, the effects of afocal size lenses on near heterophoria were evaluated, demonstrating that these lenses do not merely enlarge images but are also able to influence accommodative and vergence posture. A theoretical model which partially explains these findings is presented