Objective: To compare the psychometric performance of Spanish versions of the 25-item National Eye Institute Visual Function Questionnaire (NEI VFQ-25) and the NEI VFQ-39 administered to Latino patients with the psychometric performance of the standard English NEI VFQ-25 and NEI VFQ-39 administered to non-Latino patients.
Design: Clinic-based cross-sectional survey.
Participants: Four hundred three patients (160 Latinos and 243 non-Latinos) recruited from general ophthalmology clinics of an urban public hospital over a 6-month period.
Methods: Structured face-to-face interviews were conducted in Spanish and English to collect data for the NEI VFQ-25 and NEI VFQ-39. We calculated the mean, standard deviation, and percentage of participants having the minimum (floor) and maximum (ceiling) possible score for each item and scale. Internal consistency reliability of the NEI VFQ-25 and NEI VFQ-39 was estimated using the Cronbach alpha and average inter-item correlation. Construct validity for the instruments was assessed by comparing scores for participants classified as having normal versus impaired visual acuity.
Main outcome measures: Instrument scales for general health; general vision; ocular pain; near activities; distance activities; vision-specific social functioning, mental health, role difficulties, and dependency; driving; color vision; and peripheral vision.
Results: Internal consistency reliability was significantly lower in the Spanish version than in the English version for 3 scales of the NEI VFQ-25. More importantly, 3 scales in the Spanish version manifested inadequate reliability (alpha< or =0.70), compared with only 1 inadequately reliable subscale in the English version. Reliability coefficients associated with the Spanish NEI VFQ-39 scales exceeded commonly accepted minimum standards. Comparison of reliability coefficients between Latino and non-Latino subgroups demonstrated statistically significant differences for 4 scales: Ocular Pain, Mental Health, Role Difficulties, and Dependency. In each case, the Latino group had the lower internal consistency reliability. However, only for the Ocular Pain subscale was reliability both significantly lower and inadequate (alpha<0.70).
Conclusion: Overall performance of the NEI VFQ in Latino populations is adequate. However, in the absence of modifications to improve the reliability of specific Spanish version subscales, comparisons between Latino and non-Latino subgroups using the NEI VFQ must be interpreted with appropriate caution.