Psychometric validation of the national eye institute visual function questionnaire - 25 (NEI VFQ-25) French version - In a population of patients treated for ocular hypertension and glaucoma

Objective: Physicians need reliable, valid and sensitive questionnaires to assess QOL related to glaucoma or ocular hypertension. This article presents the psychometric properties of the French version of the National Eye Institute Visual Function Questionnaire - 25 (NEI VFQ-25). Methods: A mail survey was sent to 20 000 households. The survey identified 581 residents with glaucoma or ocular hypertension. Of these a random sample (n = 204) took part in a telephone survey during which the NEI VFQ-25 was completed by eligible patients (those taking at least one topical treatment for glaucoma or ocular hypertension on the day of the interview). Multi-trait analysis was performed to assess the construct validity of the questionnaire. Internal consistency reliability was assessed using Cronbach's alpha and the average inter-item correlation. Known groups validity was assessed by comparing patients grouped by duration of glaucoma, adjusted for age and gender. Results: One hundred and seventy-three patients participated in the survey. Analysis of convergent validity showed that all of the items in each scale correlated above 0.40 with their own scale except for the 'driving' scale. The success rate of the discriminant validity ranged from 57.1% to 100% except for the 'driving' scale, which was 7.1%. Cronbach's alpha coefficients were all above 0.70 except the 'driving' score. Participants with glaucoma for less than 20 years consistently had better 'global', 'near vision', 'distant vision', 'driving', 'social function' and 'peripheral vision' scores than those with disease of 20+ years duration, indicating better QOL in patients with a shorter disease duration. Conclusion: The NEI VFQ-25 is a validated instrument to measure vision-targeted QOL in French populations with glaucoma.