Diffuse brain damage in normal tension glaucoma

Brain changes within and beyond the visual system have been demonstrated in primary open angle glaucoma (POAG), the most common type of glaucoma. These changes have been often interpreted as a neurodegenerative process due, at least partially, to the raised intraocular pressure (IOP). In this context, normal tension glaucoma (NTG), a form of POAG with IOP <21 mm Hg despite the typical glaucomatous findings, represents the most suitable model of glaucoma to test the validity of this hypothesis. We acquired multimodal brain MRI in NTG patients (n = 17) and compared them with demographically matched groups of POAG patients with raised IOP (n = 17) and normal controls (NC, n = 29). Voxelwise statistics was performed with nonparametric permutation testing. Both NTG and POAG patients showed, compared to NC, significantly more gray matter atrophy in both the visual system and in nonvisual brain regions and altered diffusion tensor imaging-derived anatomical connectivity (AC; lower fractional anisotropy and/or higher diffusivities). Compared with NTG, POAG had both more atrophic visual cortex and higher axial diffusivity in nonvisual regions. Functional connectivity (FC) with respect to NC was altered in NTG at short-range level [visual network (VN), ventral attention network] and in POAG at long-range level (between secondary VN and limbic network). FC of POAG was higher than NTG in both VN and executive network. This study provides further evidence that diffuse structural and functional abnormalities across glaucoma brain may be, at least partially, independent of raised IOP and the consequent retinal degeneration. This further defines glaucoma as a condition with neurodegeneration spreading. Hum Brain Mapp 39:532-541, 2018. © 2017 Wiley Periodicals, Inc.