Optical coherence tomography in idiopathic REM sleep behavior disorder (RBD)

Objectives: Optical coherence tomography (OCT) is a noninvasive technique that allows imaging of the retinal nerve fi ber layer (RNFL). A reduction of the RNFL thickness has been found in several neurological disorders, including Parkinson Disease (PD). Aim of this study was to investigate RNFL thickness in patients with idiopathic REM sleep behavior (iRBD), a key symptom of the premotor stage of PD. Methods: Fifteen videopolysomnography-con fi rmed iRBD patients (14 males, 69.4 7 years) underwent OCT, 123I-FP-CIT-SPECT to assess Dopamine Transported (DAT) levels, and color testing. We measured RNFL thickness of temporal and nasal regions in both eyes and computed an asymmetry index in nasal and temporal regions (mean of the upper and lower quadrants), respectively. Thirteen healthy volunteers (seven males, 65.6 4 years) served as control group for OCT data. Correlation was searched for between RNFL asymmetry index and i) DAT striatal binding ratios (SBR) and asymmetries; ii) quantitative parameters of REM sleep without atonia (RWA). Results: Compared to controls, iRBD patients showed a signi fi cantly (P = 0.02) higher asymmetric RNFL index in the nasal regions only. No signi fi cant correlation was found between OCT data and either DAT SBR or RWA parameters. Conclusions: This very preliminary data shows that OCT RNFL asymmetry might be an early sign of neurodegeneration in iRBD patients, possibly unrelated to striatal DAT levels or RWA severity. Neurodegenerative disorders often manifest with an asymmetric pattern at the very beginning; the present data needs to be explored in a larger series.