MRI-Based Texture Analysis of the Extraocular Optic Nerve in Idiopathic Parkinson's Disease

Objective: To evaluate microstructural and morphological alterations of the extraocular optic nerve in patients with idiopathic Parkinson's disease (IPD) using MRI-based texture analysis and to compare these findings with those of healthy controls. Methods: This retrospective study included 74 participants (37 IPD patients and 37 age- and sex-matched controls). IPD diagnosis was established according to the UK Parkinson's Disease Society Brain Bank criteria. Coronal T2-weighted images obtained from a 1.5-T MRI system were retrospectively analyzed. A round region of interest was placed on the intraorbital extraocular segment of the optic nerve for histogram-based and radiomic texture analyses. Optic nerve sheath diameter (ONSD) was also measured. As no significant differences were observed between right and left eyes, the mean value of both eyes was used for statistical analyses. Statistical analyses included independent samples t-test, Mann-Whitney U test, and chi-square test. Results: No significant differences were observed between groups regarding age or sex (p > 0.05). ONSD was significantly greater in the IPD group than in healthy controls (5.2 ± 0.8 mm vs. 3.2 ± 0.5 mm, p < 0.05). Histogram analysis demonstrated significantly lower entropy values in patients with IPD (p < 0.05). In GLRLM analysis, short-run emphasis and high gray-level run emphasis were significantly lower, whereas long-run emphasis and low gray-level run emphasis were significantly higher in the IPD group (p < 0.05). GLSZM analysis revealed increased small zone emphasis and decreased large zone emphasis parameters in patients with IPD compared with controls (p < 0.05). Conclusions: MRI-based texture analysis reveals significant structural and microstructural alterations in the extraocular optic nerve in IPD, supporting its potential role as a non-invasive imaging biomarker for subclinical visual pathway involvement.