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D. A. Leske, S. R. Hatt, J. M. Holmes; Defining Real Change of Health Related Quality of Life Scores in Adults With Strabismus. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1987.
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Treatment for strabismus aims to improve function and health related quality of life (HRQOL), but real change in HRQOL scores has not been rigorously defined using test-retest data. The purpose of this study is to define real change in HRQOL scores in a cohort of strabismus patients using strabismus-specific and general vision-related HRQOL instruments.
12 adult patients with stable strabismus and no intervening treatment completed the NEI VFQ-25 and the new Adult Strabismus 20 (AS-20) HRQOL instruments. Questionnaires were completed a second time at a subsequent office visit. Test-retest differences were compared and 95% limits of agreement (LOA), a threshold value for real change, were calculated for composite scores and subscale scores.
As expected for a test-retest study, no statistically significant changes were seen in composite HRQOL scores or subscale scores for either the AS-20 or VFQ-25 (P = 0.08 to 1.0, signed rank). For the AS-20, the 95% LOA for the composite score was 17.3 points. The 95% LOA was 25.9 for the AS-20 functional subscale and 19.2 for the AS-20 psychosocial subscale. For the VFQ-25 composite score, the 95% LOA was 14.0. 95% LOAs for the VFQ-25 subscales ranged from 0 (no variability due to a ceiling effect) to 56.6 (large variability). Previous studies have identified peripheral vision and vision-specific social functioning, mental health, role difficulties, and dependency subscales as useful for diplopic patients but not non-diplopic patients. These subscales had 95% LOAs of 45.9, 21.2, 28.7, 24.7 and 12.1 respectively.
A change of 17 points or more on the AS-20 is indicative of a real change of HRQOL in patients with strabismus. The VFQ-25 may be less useful for quantifying strabismus-specific HRQOL issues due to ceiling effects, large variability, and large LOA’s on several subscales. These data can now be used for responsiveness studies to further evaluate the usefulness of these instruments in assessing HRQOL of adults with strabismus.
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