Dose-Related, Layer-Specific Alterations in Macular Microcirculation Following Horizontal Rectus Muscle Surgery: A Three-Dimensional OCT Angiography Study

Purpose: To investigate dose-related, layer-specific, and regional changes in macular microcirculation after horizontal rectus muscle surgery using three-dimensional optical coherence tomography angiography (3D-OCTA). Methods: This prospective observational study included 40 eyes from 30 patients. Eyes were grouped by cumulative surgical dose (supranormal ≥14 mm, n=15; conventional <14 mm, n=25). Macular 6×6-mm OCTA was obtained preoperatively and at postoperative day 1, week 2, and week 6. Three-dimensional vessel volume density (VVD), vessel skeleton density (VSD), and vessel diameter index (VDI) were quantified in the superficial vascular plexus (SVP), intermediate capillary plexus (ICP), and deep capillary plexus (DCP) across ETDRS subfields and a whole-scan region. Longitudinal changes were assessed using generalized estimating equations with Holm-adjusted contrasts versus baseline, and dose–response relationships using Spearman correlation. Results: Supranormal-dose eyes showed early reductions in VVD and VSD of the DCP on day 1, most evident in outer-ring sectors and the whole-scan region. Increases in both the SVP and ICP emerged at week 2, while residual deep-layer abnormalities persisted in selected sectors at week 6. Conventional-dose eyes showed no early decline but demonstrated compensatory increases at week 2 and sustained DCP dilation through week 6. Higher dose correlated with smaller ΔVVD and ΔVSD responses in nasal and superior sectors and greater temporal deep-layer ΔVDI. Conclusions: Horizontal rectus muscle surgery induces dose-sensitive macular microvascular alterations, with higher doses preferentially affecting the DCP and showing slower recovery in selected regions. 3D-OCTA enables sensitive detection of these changes and may assist in surgical planning and postoperative monitoring.