Validation of the Utah Photophobia Symptom Impact Scale (version 2) as a headache-specific photophobia assessment tool.

OBJECTIVE: To present an updated version of the Utah Photophobia Symptom Impact Scale version 2 (UPSIS2), providing robust clinical and psychometric validation, to improve headache-specific evaluation of light sensitivity and headache-related photophobia. BACKGROUND: The original UPSIS filled a gap in available tools for assessment of headache-associated light sensitivity by providing patient-reported evaluation of the impact of light sensitivity on activities of daily living (ADLs). We have since revised the original questionnaire to provide a more robust item construct and refined validation approach. METHODS: We conducted a psychometric validation of the UPSIS2 through a primary analysis of an online survey of volunteers with recurrent headaches recruited from the University of Utah clinics and surrounding community. Volunteers completed the original UPSIS and UPSIS2 questionnaire versions in addition to measures of headache impact, disability, and frequency. The UPSIS2 now includes a pre-defined recall period and a 1-4 Likert scale with standardized response anchors to improve clarity. Internal construct validity, external construct validity, and test-retest reliability, were evaluated. RESULTS: Responses were obtained from 163 volunteers, with UPSIS2 scores ranging from 15 to 57 (out of a possible 15-60) with a mean (standard deviation) of 32.4 (8.80). Construct validity was satisfactory, as evidenced by sufficient unidimensionality, monotonicity, and local independence. Reliability was excellent, with Rasch test reliability = 0.90 and Cronbach's alpha = 0.92, and an intraclass correlation of 0.79 (95% confidence interval 0.65-0.88) for participants who took the test twice. UPSIS2 correlates well with other headache measures (Spearman's correlations >0.50), as well as the original UPSIS (Spearman's correlation = 0.87), indicating good convergent validity. UPSIS2 scores differ significantly across International Classification of Headache Disorders (third edition) groups, indicating good known group validity. CONCLUSION: The UPSIS2 provides a well-validated headache-specific outcome measure for the assessment of photophobia impact on ADLs.