Purpose: To develop and validate the Functional Reading Independence (FRI) Index, a new patient-reported outcome measure assessing reading activities in individuals with geographic atrophy (GA) due to age-related macular degeneration.
Methods: The Index was developed through expert consultation and qualitative patient interviews. Reliability, validity, and responsiveness were tested with data from the Mahalo study (NCT01229215) of lampalizumab in patients with GA.
Results: Qualitative interviews (n = 40) yielded a 10-item FRI Index, which was refined to seven items in quantitative testing (n = 100). Strong internal consistency (marginal reliability = 0.90) and reproducibility (intraclass correlation coefficient = 0.86) were shown. Known-group validity testing for baseline mean FRI Index scores showed differences (mean [SD]) between patients with Minnesota Low-Vision Reading test reading speed ≥80 vs. <80 words per minute (3.0 [0.7] vs. 1.9 [0.7]; P < 0.001), and between patients above vs. below median values on the National Eye Institute Visual Function Questionnaire-25 (NEI-VFQ-25) score (2.9 [0.7] vs. 2.1 [0.8]; P < 0.001). Convergent validity with binocular measures was strong (Spearman's correlation = 0.72 for reading speed, 0.66 for NEI-VFQ-25). Analysis of sensitivity to change revealed mean FRI Index score changes for patients with GA lesion size growth ≥2.5 mm2/18 months of -0.41 (0.70) vs. -0.13 (0.61) for patients with lesion growth <2.5 mm2/18 months (P = 0.07).
Conclusions: The FRI Index demonstrated good reliability and validity in patients with GA. Further study in a broader GA population is warranted to confirm responsiveness.