The purpose of the study was to develop a questionnaire that could quantify the quality of life (QOL) of people with refractive correction by spectacles, contact lenses, and refractive surgery in the prepresbyopic age group.
The questionnaire was developed and validated using traditional methods and Rasch analysis. A 90-item pilot questionnaire was developed through extensive literature search and use of professional and lay focus groups. Pilot study data were obtained from 306 subjects for item reduction to produce the 20-item Quality of Life Impact of Refractive Correction (QIRC) questionnaire. Validity and reliability studies (test-retest reliability with intraclass correlation coefficient and Bland-Altman limits of agreement, and internal consistency with Rasch fit statistics, factor analysis, and Cronbach’s α) were performed from data of an additional 312 subjects.
Rasch analysis demonstrated QIRC has good precision, reliability, and internal consistency (person separation, 2.03; reliability, 0.80; root-mean-square measurement error, 3.25; mean square ± SD infit, 0.99 ± 0.38; outfit, 1.00 ± 0.39; item infit range, 0.70 to 1.24; and item outfit range, 0.78 to 1.32). The items (mean score, 50.3 ± 7.3) were well targeted to the subjects (mean score, 47.8 ± 5.5) with a mean difference of 2.45 (scale range, 0 to 100) units. Test-retest reliability (intraclass correlation coefficient, 0.88; coefficient of repeatability, ±6.85 units), factor loading range (0.40 to 0.76), and Cronbach’s α (0.78) also indicated the reliability and validity of QIRC.
The 20-item QIRC questionnaire, which quantifies the QOL of people with refractive correction by spectacles, contact lenses, and refractive surgery in the prepresbyopic age group, was developed using Rasch analysis and shown to be valid and reliable. The use of Rasch scaling allows scores to be treated as a valid continuous variable. QIRC has broad applicability for cross-sectional and outcomes research.
Department of Optometry, University of Bradford, Bradford, West Yorkshire, United Kingdom
Supported by a grant from Johnson & Johnson Vision Care Europe. NHMRC Sir Neil Hamilton Fairley Fellowship 007161 supports K. Pesudovs. Ultralase provided access to refractive surgery subjects.
Received February 10, 2004; accepted June 16, 2004.