Psychometric properties of the WHO-VFQ-20 questionnaire for assessing vision-related quality of life in Brazilian urban populations with different vision status.

This study aimed to analyze the psychometric properties of the 20-item WHO-Visual Functioning Questionnaire (WHO-VFQ-20). Ordinal data and Rasch analysis were performed to determine instrument precision (internal consistency and reliability) and validity (fit statistics and dimensionality). The WHO-VFQ-20 was administered to 606 adult participants with different ocular conditions and visual acuity levels, stratified by age, sex, and socioeconomic status, from three Brazilian urban populations-a public hospital and two non-governmental institutions located in the outskirts of Sao Paulo city. Ordinal data analysis showed a mean global score of 59.6 ± 25.0 s.d., which consistently reduced with decreasing visual acuity. Higher scores were significantly associated with better overall health, higher education, and being married/cohabitating. Cronbach's alpha coefficient of 0.94 indicated excellent internal consistency. Rasch analysis demonstrated good measurement precision with reliability coefficients of 0.99 and 0.85 for items and persons, respectively. Three items related to ocular pain and mental well-being were identified as misfitting. The variance explained by the measures suggested multidimensionality. Analyzing the instrument as two components (visual functioning and psychosocial functioning) yielded improvement on model fit, indicating acceptable precision and validity of the WHO-VFQ-20 for assessing vision-related quality of life in adults from urban areas of a middle-income country.