Development and validation of the global spectacle independence questionnaire: a brief patient-reported outcome measure with U.S. population norms

Abstract Background To develop and provide initial validation evidence for the Global Spectacle Independence Questionnaire (GSIQ), a patient-reported outcome measure of spectacle independence (SI), and to provide U.S. national norms of SI. Methods Instrument development followed U.S. Food and Drug Administration and International Society for Pharmacoeconomics and Outcomes Research guidance. Concept elicitation and cognitive debriefing interviews were conducted in the U.S. ( N = 36). An online survey ( N = 960) representative of the U.S. adult population collected psychometric data to assess reliability and validity relative to the National Eye Institute Refractive Error Quality of Life Instrument-42 (NEI-RQL). The primary endpoint, GSIQ-DC, is a dichotomous classification (DC) of SI defined as responding “None of the time” to all three core items (need for vision correction, wearing vision correction, and straining/squinting without correction) during the past 7 days. Results Qualitative interviews identified concepts of spectacle independence and achieved concept saturation. The final GSIQ consists of three core items (plus one optional digital-device item). Exploratory factor analysis supported unidimensionality (60.7% variance explained). Internal consistency was strong (Cronbach’s α = 0.82); test-retest reliability was excellent (intraclass correlation coefficient = 0.87). Convergent validity with theoretically related NEI-RQL subscales was moderate to strong; known-groups analysis and logistic regression further supported validity. In the weighted U.S. normative sample, 18.8% of adults were classified as fully spectacle independent. Conclusions The GSIQ is a concise, reliable patient-reported outcome measure with evidence of validity. Its dichotomous primary endpoint provides a standardized, patient-centered measure of complete spectacle independence for evaluating vision correction interventions across clinical research settings.