Purpose: To develop measures and indices of factors (distance of eye from object, posture, and lighting) that may modify a possible effect of near work activity on myopia.
Methods: The duration of near work, the distance of an object from eye, lighting conditions, and other sociodemographic characteristics were asked in an interview. Both distance and lighting information from the questionnaire were compared with more precise measurements.
Results: Diopter hours were quantified as the duration of near work multiplied by the reciprocal of the distance which the activity was performed. The intraclass correlation coefficient of the reliability of distance information for each type of near work activity ranged from 0.43 to 0.91. Home light meter readings were significantly higher for children who were reading under both room and reading light, and the distances from the questionnaire were comparable to the measured distances.
Conclusions: Measures of posture, distance, and lighting factors have been developed to study the possible effect modifiers of the effects of near work on myopia.