Abstract： Objective To evaluate the brain white matter abnormality in the chronic primary angleclosure glaucoma (PACG) subjects with magnetic resonance diffusion tensor imaging (DTI), and to identify the abnormal regions in white matter based on altered fractional anisotropy (FA). Methods A retrespective study was conducted on the data of patients who underwent brain magnetic resonance imaging (MRI) at Department of Ophthalmology, Tianjin Medical University General Hospital between 2008 and 2009. Twenty-five patients who were proved to have chronic PACG and received brain DTI scan were recruited in the study (chronic PACG group), and were further stratified into the mild chronic PACG group and the severe chronic PACG group according to severity of visual field loss. A contemporary cohort of 25 healthy subjects who also underwent brain DTI scan was recruited as normal controls. FSL and Dtlstudio software were applied to process the raw data and to calculate the FA map which was then entered into the SPM5 software for normalization and grey/white matter segmentation. Then the segmented FA map of white matter was smoothed.Two-sample t test was used to compare the FA map in the chronic PACG group and the normal control group.The comparison was further controlled by family-wise error (FEW). Significantly different regions (as defined by P value less than 0.05) were overlaid on the normalized template, with the display threshold being 10 voxels. The same algorithm was used to compare the FA map between mild and severe chronic PACG groups.Results Each three subjects from the chronic PACG group and the normal control group were excluded due to obvious head motion, so that there were 22 subjects in each group. The chronic PACG group comprised 13 cases of mild and 9 of severe chronic PACG. Compared with the normal controls, the FA value at the root of bilateral optic tracts was significantly reduced among patients with chronic PACG (98 voxels on the left and 56 voxels on the right, P＜0.05, adjusted by FEW). There was no difference in FA value between the mild and severe chronic PACG groups (P＞0.05). Conclusions DTI can be used to investigate the brain white matter changes in chronic PACG. FA value may be a useful indicator for abnormality at the root of bilateral optic tracts.