Abstract
OBJECTIVE: To investigate the relationship between baseline subfoveal choroidal thickness (SFChT) and both visual outcomes and geographic atrophy (GA) growth rate, and to assess whether SFChT mediates the treatment effect of oral metformin on GA progression. DESIGN: Secondary analysis of a randomized controlled trial. PARTICIPANTS: Seventy eyes (34 metformin; 36 observation) from 44 participants (21 metformin; 23 observation) with GA and ≥6 months of follow-up in the METformin for the MINimization of Geographic Atrophy Progression study. METHODS: Subfoveal choroidal thickness was measured from baseline OCT. We calculated GA area growth rate by subtracting the GA area at the first visit from the GA area at the last visit and dividing the result by the time interval. Geographic atrophy perimeter-adjusted growth rate was calculated by dividing GA area growth rate by the mean GA perimeter between the first and last visit. MAIN OUTCOME MEASURES: Longitudinal changes in GA area and visual acuity. RESULTS: Baseline SFChT was not significantly associated with baseline GA area (P = 0.51), baseline best-corrected visual acuity (BCVA) (P = 0.49), baseline low-luminance visual acuity (LLVA) (P = 0.85), or rim area focal hyperautofluorescence signals (P = 0.29). Baseline SFChT was not significantly associated with GA perimeter-adjusted growth rate (P = 0.74), the decline rate of BCVA (P = 0.14), and the decline rate of LLVA (P = 0.71). However, sensitivity analyses in GA subgroups found that baseline SFChT was associated with decreased rate of BCVA decline in patients with foveal-involving GA (Spearman ρ = 0.03, P = 0.03). Baseline SFChT did not significantly influence the effect of oral metformin on GA perimeter-adjusted growth rate (P = 0.78). CONCLUSIONS: Greater baseline SFChT was significantly associated with slower BCVA decline in eyes with foveal-involving GA, suggesting a possible localized role of choroidal thickness in preserving central vision. However, SFChT was not associated with GA growth rate, LLVA decline, or baseline anatomical and functional measures. It also did not mediate the effect of oral metformin. While SFChT lacks prognostic value for GA progression overall, it may hold limited relevance for central vision outcomes in foveal-involving GA. FINANCIAL DISCLOSURES: Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.