The psychometric validity of the NEI VFQ-25 for use in a low-vision population

Purpose. To determine the psychometric validity of the National Eye Institute-Visual Function Questionnaire (NEI VFQ- 25) and its subscale structure for use in people with low vision. Methods. Two hundred thirty-two participants completed the NEI VFQ-25. Rasch analysis was used to test the psychometric performance of the questionnaire and each subscale. Factor models were hypothesized and tested with confirmatory factor analysis (CFA) and subsequently validated with Rasch analysis. Results. For the overall scale, two rating scales had to be dichotomized and three misfitting items removed to improve fit to the Rasch model. There was evidence of multidimensionality, indicating that the scale would benefit from scale splitting. For the NEI VFQ-25 subscale structure, six of the original 12 subscales could not fit the Rasch model because of item insufficiency (fewer than two items) and the remaining six displayed poor item fit characteristics indicating that the NEI VFQ-25 does not have a viable subscale structure. CFA supported a two-factor model with visual functioning (10 items) and socioemotional (9 items) scales. Most goodness-of-fit statistics were within the recommended range of values. The factor loadings of items on their respective scales were statistically significant (P_0.001) and ranged between 0.59 and 0.84. The two scales individually fitted the Rasch model and were found to be unidimensional with adequate psychometric characteristics. Conclusions. The native NEI VFQ-25 is a better performing instrument when split into visual functioning and socioemotional scales. These scales possess valid parameters for assessment of the impact of low vision in this population.