Test–Retest Reliability of Health-Related Quality-of-Life Questionnaires in Adults with Strabismus

Abstract

To report the test-retest variability of two health-related quality-of-life instruments: the new Adult Strabismus 20 (AS-20) and the National Eye Institute 25-item Visual Function Questionnaire (NEI VFQ-25), in adults with strabismus. Prospective case series. Fifty-five adult patients in a clinical practice with stable strabismus completed the AS-20 and the NEI VFQ-25 at 2 visits, without intervening treatment. Questionnaires were completed the second time either at a subsequent office visit, immediately before surgery, or by mail. Intraclass correlation coefficients were calculated. Ninety-five percent limits of agreement and 95% confidence intervals around the 95% limits of agreement also were calculated. There was excellent agreement of overall questionnaire scores for the AS-20 (intraclass correlation coefficient, 0.92) and NEI VFQ-25 (intraclass correlation coefficient, 0.94). The 95% limits of agreement for overall scores were 14.3 points (95% confidence interval, 10.9 to 17.7) for the AS-20 and 11.1 points (95% confidence interval, 8.5 to 13.8) for the NEI VFQ-25. The lower test-retest variability of the VFQ-25 seemed to be partly the result of ceiling effects with many scores at the normal end of the range. The new AS-20 and the NEI VFQ-25 show excellent test-retest reliability in adults with strabismus. Change exceeding 95% limits of agreement (14 points on the AS-20 and 11 points on the VFQ-25) is indicative of real change in an individual patient. The AS-20 may be more useful than the VFQ-25 because it is less prone to ceiling effects in adults with strabismus.