White Matter Alterations of Visual Pathway in Thyroid Eye Disease: A Fixel‐Based Analysis

Background Thyroid eye disease (TED), particularly its sight‐threatening complication, dysthyroid optic neuropathy (DON), profoundly impacts patients' visual health. The pathological changes in the white matter (WM) fibers within the intracranial visual pathway in TED have been infrequently studied. Understanding these changes holds crucial importance for exploring the pathogenesis and prognosis of TED. Purpose To utilize fixel‐based analysis (FBA) to clarify the type of microstructural damage occurring in the visual pathway in TED. Study Type Prospective. Subjects 28 TED with DON patients (11 males and 17 females), 28 TED without DON (non‐DON) patients (12 males and 16 females), and 28 healthy controls (HCs) (12 males and 16 females). Field Strength/Sequence 3 T; multishell diffusion MRI using echo planar imaging. Assessment Fiber density (FD) and fiber‐bundle cross‐section (FC) were calculated to characterize WM microstructural alteration in TED visual pathway. The correlations between FBA metrics and visual field index and mean deviation were examined. Statistical Tests One‐way analysis of variance, Kruskal–Wallis, t ‐tests, Mann–Whitney U, Chi‐square, and Pearson correlation, were conducted with false discovery rate and family wise error corrections. Significance was set at P < 0.05. Results Both DON and non‐DON groups showed significant FD loss in the right optic tract compared with HCs, with DON patients experiencing more severe FD loss. Only DON patients had FD loss in the right optic radiation (OR) compared with the non‐DON patients and HCs, with no FC difference across groups. FD in DON patients' ORs significantly correlated with visual field index ( r = 0.857) and mean deviation ( r = 0.751). Data Conclusion Both DON and non‐DON affect the WM microstructure of the visual pathway to varying extents. Visual field metrics can reflect the severity of FD damage to the OR in the visual pathway of DON patients. Evidence Level 2. Technical Efficacy Stage 3.