Optical coherence tomography-based cross-sectional measurement of the fovea–Bruch’s membrane opening angle after intraocular pressure-lowering surgery

Background/Aims To introduce a novel cross-sectional optical coherence tomography (OCT) parameter describing the relative position of the optic nerve head (ONH) from a fovea-based perspective and investigate its change after intraocular pressure (IOP)-lowering glaucoma surgery. Methods 39 eyes of 38 patients who underwent glaucoma filtration surgery were included. Spectral-domain OCT images were obtained along the ONH–fovea axis before and after surgery. The fovea–Bruch’s membrane opening (BMO) angle was defined as the angle at the temporal BMO point between the line connecting the nasal and temporal BMO points and the line connecting the temporal BMO to the fovea. Preoperative and postoperative fovea–BMO angles were compared, and factors associated with angle change were evaluated using linear regression analysis. Results The average IOP reduction after surgery was 11.9±8.7 mm Hg, and the postoperative IOP was 12.9±5.2 mm Hg. The fovea–BMO angle decreased from 174.9°±2.8° to 173.6°±3.0° (p<0.001), indicating a small but statistically significant change in the temporal peripapillary area with IOP reduction. The fovea–BMO angle change was associated with the amount of IOP reduction (p=0.040) and axial length (p=0.014). Conclusion IOP-lowering surgery was associated with a mild but significant decrease in the fovea–BMO angle, suggesting steepening of the temporal peripapillary contour. Further investigations into the clinical significance of this new finding may be beneficial to comprehensively understand the biomechanical aspects of the temporal peripapillary area in glaucoma surgery.