LAUSR

Purpose To seek the threshold value of Bruch’s membrane opening-minimum rim width (BMO-MRW) where visual field (VF) damage occurs in open-angle glaucoma (OAG) and explore whether there are structural differences between primary open-angle glaucoma (POAG) and normal-tension glaucoma (NTG). Methods We recruited 83 healthy and 106 glaucoma (49 with POAG and 57 with NTG) subjects for this study. All subjects underwent optical coherence tomography (OCT), BMO-MRW scans, and Humphrey visual field (VF) analyzer examination. Global and sectoral BMO-MRW was correlated with the corresponding VF according to the Garway-Heath map. Using a broken-stick statistical model, the structure–function relationship of VF values and BMO-MRW, the tipping point where VF defects were associated with a reduction in BMO-MRW and the slopes above and below the tipping point were determined and compared between POAG and NTG. Results The tipping point of global BMO-MRW for VF impairment was 234.38 μm, 228.09 μm, and 249.68 μm in the OAG, POAG, and NTG groups, respectively. The slope below the tipping point was significantly steeper than the slope above it in all quadrants of each group ( p  < 0.001). The tipping point in NTG in the inferotemporal and nasal quadrants was smaller than that of POAG, especially in the inferotemporal quadrant. Conclusion In OAG, BMO-MRW loss seems to occur before the onset of perimetric impairment. Compared with POAG, NTG appears to have more severe rim damage, especially in the inferotemporal quadrant at the onset of detectable VF defects.