The eye-complaint questionnaire in a visual display unit work environment: internal consistency and test-retest reliability

The internal consistency and test-retest reliability of a 10-item eye-complaint questionnaire (ECQ) were examined within a sample of office workers. Repeated within-subjects measures were performed within a single day and over intervals of 1 and 7 d. Questionnaires were completed by 96 workers (70% female, mean age 36.4 years) who perform more than 4 h of visual display unit work each day. The internal consistency of the ECQ was high (alpha = 0.801). Although test-retest reliability was low within a single day (morning and afternoon) (intra-class correlation coefficient (ICC) = 0.68, 95% CI 0.38, 0.82), it was good between two morning measurements over a 1-d interval (ICC = 0.91 95% CI 0.87, 0.94) and between morning measurements with a 7-d interval (ICC = 0.87, 95% CI 0.81, 0.92). The ICC between afternoon measurements over a 1-week interval was moderate (ICC = 0.78, 95% CI 0.66, 0.85). This questionnaire is a reliable and consistent instrument for easily assessing eye complaints in office work. The timing of the measurements must be kept in consideration since measurements are confounded by exposures over the day.