Voxel Based Analysis of Diffusion Indices in Patients with Primary Open-Angle Glaucoma Using Tract-Based Spatial Statistics

Background and purpose: Diffusion tensor imaging can provide information about microstructural changes of the visual pathway in glaucoma patients. Tract-based spatial statistics (TBSS) has been established for analysis of fractional anisotropy (FA) and has successfully been used for analysis of DTI data of glaucoma patients. However there are certain DTI indices such as mean diffusivity (MD), radial diffusivity (RD), axial diffusivity (AD) and mode of anisotropy (MO), which can also be analyzed using TBSS. Hence, we tested whether TBSS is useful for analysis of non-FA data in glaucoma patients and for identification of microstructural changes in patients with primary openangle glaucoma characterized by these non-FA DTI indices. Material and methods: Our study comprised 46 patients with primary open-angle glaucoma (POAG) and a healthy, age-matched control group of 23 subjects. TBSS was used for analysis of FA as well as MO, MD, RD and AD. Results: For an automated analysis of non-FA diffusion indices we could establish a workflow using TBSS in addition to its primary purpose, the analysis of FA. Our results reveal clusters of voxels with overlapping decreased FA and increased RD and MD in the optic radiation as well as in visual association tracts. Conclusion: TBSS is a useful tool not only for analysis of FA but also of non-FA diffusion indices in glaucoma patients. Overlapping decreased FA and increased MD and RD can be found in POAG patients not only in the optic radiation but also in visual association tracts, suggestive for significant neurodegeneration in POAG.