Structure–Function Relationships in Retinitis Pigmentosa: Three-Year Changes in Visual Function and Outer Retinal Layers

PURPOSE: To characterize longitudinal changes in outer retinal layers in retinitis pigmentosa (RP) and to determine how these structural alterations relate to functional decline, including visual field parameters and visual acuity. METHODS: In this retrospective cohort study, 57 eyes with RP were evaluated over a fixed 3-year follow-up. Annual measurements of ellipsoid zone width (EZW), outer nuclear layer (ONL) thickness, and outer segment (OS) thickness were obtained from horizontal foveal OCT scans. Functional assessments included best-corrected visual acuity (BCVA) and visual field index (VFI), mean deviation (MD), and pattern standard deviation (PSD). Linear mixed-effects models were used to estimate longitudinal rates of change and structure-function associations. RESULTS: All visual field parameters significantly declined over time (VFI: -2.06%/year; MD and PSD both P < 0.050). Structural parameters also demonstrated progressive deterioration (EZW: -2.7%/year, P < 0.001; ONL: -1.82 µm/year, P = 0.038; OS: -1.25 µm/year, P = 0.006). Among structural measures, EZW demonstrated the strongest association with VFI (P < 0.001), while OS thickness showed the closest relationship with BCVA (P = 0.002). ONL thinning was significant but showed limited functional correlation. CONCLUSIONS: Distinct outer retinal biomarkers were differentially associated with functional measures in RP. Repeated EZW measurements were most strongly associated with VFI, whereas repeated OS thickness measurements were most closely associated with BCVA. ONL shows measurable structural loss but limited functional relevance. Multilayer structural assessment provides complementary information on RP progression and may help refine future clinical evaluation strategies.