Glymphatic system impairment in normal tension glaucoma evaluated by diffusion tensor image analysis along the perivascular space

Disruption of the glymphatic system plays a vital role in pathogenesis of neurodegeneration in normal tension glaucoma (NTG). We evaluated the impairment of glymphatic system of NTG patients by diffusion tensor image analysis along the perivascular space (DTI-ALPS), and explored the correlation between the ALPS index and dysfunction of visual cortices in resting state. DTI-ALPS was applied to 37 normal controls (NCs) and 37 NTG patients. Multidirectional diffusivity maps and fractional anisotropy (FA) maps were reconstructed to calculate ALPS index. The Amplitude of low-frequency fluctuation (ALFF) in visual cortices (V1-V5) were calculated using resting-state fMRI. Clinical data and ALPS indexes were compared between the groups. Lateralization of ALPS indexes and differences in visual field of two eyes were analyzed. Subsequently, regression analyses between ALPS indexes and mean deviation (MD) values of bilateral eyes and ALFF of visual cortices were performed. The bilateral ALPS indexes of NTG patients decreased significantly. In NCs and NTG patients, ALPS indexes in right hemisphere were lower than that in left hemisphere. The right ALPS indexes of NTG patients were positively correlated with the MD values of the left eyes. In NTG patients, decreased ALFF was detected in right V1 and bilateral V2-5, and the left ALPS indexes were positively correlated with ALFF in bilateral V1, V2, V5, and right V3V area. The ALPS index decreased in NTG patients, correlated with visual defects and ALFF, indicating impairment of the glymphatic system and the potential to be a biomarker in the future.