OBJECTIVES: Visual acuity does not fully capture the effect of geographic atrophy (GA), secondary to age-related macular degeneration, on visual function. The Functional Reading Independence (FRI) Index is a 7-item patient-reported measure developed for use in GA trials. This study examined the sensitivity of the FRI Index to change in GA lesion size.   METHODS: Post hoc analyses were conducted with data from MAHALO, a phase 2 study of lampalizumab, a complement factor monoclonal antibody fragment, for treatment of GA. For each reading activity performed in the past 7 days (e.g., writing checks or reading medicine labels), patients were asked the extent to which they required vision aids, adjustments in the activity, or help from another person. The FRI Index yields continuous mean scores (range 1-4) and ordinal level scores (from Level 1=Unable to do to Level 4=Totally Independent). Analysis of covariance compared mean changes in FRI Index scores stratified by more (≥0.94mm/yr) vs less (<0.94mm/yr) GA lesion growth. RESULTS: At 18 months, the mean change in FRI Index score (SD) from baseline for patients with more lesion size growth was -0.3 (0.5; n=13) vs -0.1 (0.7; n=62) for patients with less growth (P=0.02). For patients with more growth, 36% declined ≥1 FRI Level vs 15% for less growth. Excluding patients at FRI Level 1 at baseline, 41% of patients with more growth (N=54) declined > 1 FRI Level vs 18% with less growth (N=11). CONCLUSIONS: In MAHALO, the change in mean FRI Index score of 0.2 differentiated patients with more vs less growth of GA lesion size.  FRI level scores were also sensitive to GA lesion growth. These results provide evidence that patient-reported functional reading independence as measured by the FRI Index is linked to GA lesion growth, an objective clinical measure of disease progression.