Functional acuity score as a surrogate of reading performance in low vision: A Japanese disability evaluation cohort study

This retrospective cross-sectional study examined whether the Functional Acuity Score (FAS), an administrative impairment measure calculated from routine visual acuity data, was associated with reading performance in individuals undergoing formal visual disability evaluation. Thirty-one participants applying for visual disability certification at a tertiary eye hospital in Japan underwent Goldmann perimetry and MNREAD-J testing within 12 months. FAS, the Functional Field Score (FFS), and the Functional Vision Score (FVS) were calculated according to the AMA Guides. Their associations with reading outcomes, including critical print size (CPS) and the reading accessibility index (ACC), were assessed using correlation and multivariable regression analyses. FAS was strongly correlated with better-eye visual acuity (rho = 0.963) and showed the strongest associations with reading performance among the impairment measures. It was associated with CPS (rho = -0.82) and ACC (rho = 0.69) and remained associated with both outcomes in adjusted regression models, with R2 values of up to 0.76 after FAS was included. Field-based measures showed weak or inconsistent associations with reading parameters. The cohort consisted mainly of patients with glaucoma and other non-macular conditions (27/31, 87.1%). In this predominantly non-macular disability-evaluation cohort, FAS may provide an estimate of resolution-dependent reading performance when direct assessment is not available. However, only 4 of 31 participants had macular disease, and whether these findings apply to patients with macular pathology remains unclear.