Spatial Selective Choroidal Stromal and Vascular Changes in Intermediate AMD: Insights From High-Density Optical Coherence Tomography Analysis

Purpose: To characterize spatially selective alterations in choroidal angioarchitecture in intermediate AMD (iAMD) using high-density optical coherence tomography (OCT) analysis. Methods: This retrospective study analysed Spectralis OCT macular cube scans (∼61 B-scans) from 83 eyes with iAMD and 83 age-matched controls. A customized Python pipeline derived from 'Choroidalyzer' was developed to compute choroidal thickness (CT), the choroidal vascularity index (CVI), lumen area (LA), and stromal area (SA) across a 60 × 60 section of macula, yielding ∼3600 grid-level metrics. Spatial variations were evaluated using Early Treatment Diabetic Retinopathy Study sectors, and eccentricity-based modelling. Results: There were 83 eyes in each group with no difference in baseline characteristics (P = 0.135-1.00). Global analysis revealed significant reductions for CVI (-1.57%) and LA (-2.43%) in iAMD (both P < 0.0001). Spatial analysis indicated significant distinctions between outer and near-periphery rings of the Early Treatment Diabetic Retinopathy Study template (P = 0.0001-0.0096) and was supported by eccentricity analysis that showed a subfoveal increase (CVI, + 18.21%; LA, +17.77%; P < 0.0001) and parafoveal loss in iAMD eyes (CVI, -13.68 %, LA, -22.82%; P < 0.0001). Spatial analysis of CT showed linear increase with eccentricity (y = 1.16x - 1.79; R2 = 0.19; P < 0.001) with thinning subfoveally. SA demonstrated a similar pattern of loss (y = -2.081x2 + 8.72x - 8.14; R2 = 0.553; P < 0.001). Conclusions: Choroidal metrics in iAMD exhibit spatially selective changes: CT showed central thinning with minimal peripheral alterations, whereas CVI displayed subfoveal increase and parafoveal reduction. SA and LA changes mimicked CT and CVI, suggesting they drive thickness and vascularity changes, respectively. These findings suggest that the parafoveal selectivity observed in early iAMD may be secondary to choroidal vascular deficits and highlight the value of high-density OCT for detecting subtle remodeling.