title: Psychometric performance of the national eye institute 25-item visual function questionnaire: in Turkish diabetic retinopathy patients.
abstract: OBJECTIVE
  To assess the psychometric performance of the National Eye Institute 25-item Visual Function Questionnaire (NEI VFQ-25) in Turkish diabetic retinopathy patients.Reliability of the Turkish version of the NEI VFQ-25 was tested by internal consistency and test-retest reliability. Convergent validity was assessed by examining the correlation between total scores of the Turkish version of the NEI VFQ-25 and the SF-36. Principal component analysis was used to determine the best loading of items in the Turkish version of the NEI VFQ-25.
  
  
  METHODS
  Health-related quality of life was measured in a sample of 60 patients with diabetic retinopathy using both a Turkish version of the NEI VFQ-25 and the SF-36 instrument. The Turkish version of the NEI VFQ-25 was developed by following established cross-cultural adaptation and validation guidelines. After pilot testing, an interview administrator's scale for the newly translated NEI VFQ-25 was administered to 60 diabetic retinopathy patients at Haydarpasa Numune Research and Training Hospital in Istanbul, Turkey.Reliability of the Turkish version of the NEI VFQ-25 was tested by internal consistency and test-retest reliability. Convergent validity was assessed by examining the correlation between total scores of the Turkish version of the NEI VFQ-25 and the SF-36. Principal component analysis was used to determine the best loading of items in the Turkish version of the NEI VFQ-25.
  
  
  RESULTS
  The internal consistency within the domains of the NEI VFQ-25 was high, with a Cronbach's α coefficient of 0.88 for the NEI VFQ-25 scale. Reliability of the NEI VFQ-25 was also high, with a test-retest intra-class correlation value of 0.85. Significant correlations were observed between the total scores of the NEI VFQ-25 and the SF-36.
  
  
  CONCLUSIONS
  Overall, the results indicated that the psychometric performance of the NEI VFQ-25 in the study sample was very strong, and the instrument was found to be valid and reliable. The instrument is likely to be suitable for use in clinical studies of chronic eye diseases in Turkey.
authors.affiliation: 1 Department of Health Policy and Administration, Washington State University, Spokane, Washington, USA 2 The Section of the Basic Health Sciences, Marmara University Health Education Faculty, Cevizli, Kartal, Istanbul, Turkey.
authors.forename: Akinci
authors.initials: A
authors.lastname: Fevzi
authors.forename: Yildirim
authors.initials: Y
authors.lastname: Aysegul