Reliability and Construct Validity of the NEI VFQ-25 in a Subset of Patients With Geographic Atrophy From the Phase 2 Mahalo Study

Abstract

Purpose: Geographic atrophy (GA) is an advanced form of age-related macular degeneration characterized by progressive, irreversible visual function loss. This analysis evaluates the psychometric properties of the 25-Item National Eye Institute Visual Function Questionnaire (NEI VFQ-25) composite, near activity, and distance activity scores in patients with GA.

Design: Reliability and validity study.

Methods: Reliability and validity were tested with NEI VFQ-25 data collected from 100 subjects with GA from United States' sites of the phase 2 Mahalo study of lampalizumab (ClinicalTrials.gov identifier: NCT01229215).

Results: Strong internal consistency and reproducibility were demonstrated for the NEI VFQ-25 composite (Cronbach's α, 0.95; intraclass correlation coefficient [ICC], 0.86), near activity (Cronbach's α, 0.84; ICC, 0.80), and distance activity (Cronbach's α, 0.84; ICC, 0.84) scores. Convergent validity with the binocular measures, Minnesota Low-Vision Reading Test (MNRead) reading speed and Functional Reading Independence (FRI) index score, was demonstrated for baseline NEI VFQ-25 composite (Pearson correlation [r] = 0.61 and 0.69, respectively), near activities (r = 0.69 and 0.73), and distance activities (r = 0.57 and 0.64) scores. Known-group validity testing for baseline mean NEI VFQ-25 scores (composite, near activities, and distance activities) showed differences between patients with mean maximum MNRead reading speed ≥ 80 vs < 80 words per minute, and between mean FRI index score ≥ 2.5 vs < 2.5 (all P < .0001).

Conclusions: Psychometric evidence supports the NEI VFQ-25 as a reliable and valid cross-sectional measure of the impact of GA on patient visual function and vision-related quality of life.