Optic nerve integrity as a visuospatial cognitive predictor in Parkinson's disease

Objective To explore the microstructural integrity of the optic nerve and its role as a cognitive predictor in patients with de novo Parkinson's disease (PD) using diffusion tensor image-based magnetic resonance scans. Methods We enrolled 82 patients with de novo PD, 36 patients with drug-induced parkinsonism (DIP), and 36 controls. Fractional anisotropy (FA) and apparent diffusion coefficient (ADC) were measured on the mid-portion of the intraorbital optic nerve. Using a multivariate analysis of variance with repeated measures, longitudinal changes in cognitive subscores of a comprehensive neuropsychological test were evaluated in PD patients according to optic nerve integrity. Results The mean FA value in PD was significantly lower (0.552 ± 0.103, p < 0.001) than that in DIP (0.645 ± 0.099) or the controls (0.689 ± 0.089), whereas the mean ADC value was significantly higher in the PD group compared to the DIP or control group (p < 0.001). Optic nerve integrity was not associated with parkinsonian motor severity, striatal dopamine transporter activity, olfaction, or baseline cognitive performance in PD patents. In a longitudinal assessment of cognition in PD, the lower FA group showed significant decline in the performance of Clock Drawing Test (F = 3.39, p = 0.038), but no significant differences in the other cognitive subsets. Conclusion This study demonstrated that microstructural integrity in the optic nerve was distorted in PD patients, and that this nerve integrity might act as a cognitive predictor of visuospatial dysfunction.