Difference in topographic pattern of prelaminar and neuroretinal rim thinning between nonarteritic anterior ischemic optic neuropathy and glaucoma

PURPOSE. To compare the local distribution of prelaminar and neuroretinal rim (NRR) thickness between eyes with nonarteritic anterior ischemic optic neuropathy (NAION) and normal tension glaucoma (NTG) using enhanced depth imaging spectral-domain optical coherence tomography (OCT). METHODS. This cross-sectional study included pairs of NAION and NTG patients, and controls. We measured the central prelaminar thickness; Bruch’s membrane opening (BMO)— horizontal (HRW), minimal (MRW), and vertical rim widths (VRW), and vertical/horizontal thicknesses at knee of curve at rising curvature of the cup wall. HV ratio was calculated as BMO-HRW/BMO-VRW. The six thicknesses and their differences were compared. RESULTS. We had 12 pairs, with comparable visual field loss and retinal nerve fiber layer (RNFL) thickness between NAION and NTG. Within the optic nerve head (ONH), BMO-MRW, BMO-HRW, horizontal width at the knee of curve, and central prelaminar tissue showed significantly larger values in NAION compared to NTG (P < 0.05). The difference of NRR thickness between NAION and NTG increased in a centripetal manner, being maximum at the knee of curve. The mean HV ratio was 1.63 in NAION, 0.83 in NTG, and 1.06 in controls (P < 0.001). OCT showed disproportionately less altered prelaminar tissue in NAION. CONCLUSIONS. NAION and NTG showed significantly different distributions of prelaminar and NRR tissue thicknesses despite similar RNFL thicknesses, with the maximal difference being the horizontal cup wall thickness at the knee of curve. Sparing of prelaminar tissue loss characterized the ONH in NAION. OCT might aid in differential diagnosis based on local variation in thinning patterns.