Saccade, Pupil, and Blink Responses in Rapid Eye Movement Sleep Behavior Disorder

Abstract

Background: Parkinson's disease (PD) patients exhibit deficits in saccade performance, pupil function, and blink rate. Isolated REM (rapid eye movement) Sleep Behavior Disorder (RBD) is a harbinger to PD making them candidates to investigate for early oculomotor abnormalities as PD biomarkers.

Objectives: We tested whether saccade, pupillary, and blink responses in RBD were similar to PD.

Methods: RBD (n = 22), PD (n = 22) patients, and healthy controls (CTRL) (n = 74) were studied with video-based eye-tracking.

Results: RBD patients did not have significantly different saccadic behavior compared to CTRL, but PD patients differed from CTRL and RBD. Both patient groups had significantly lower blink rates, dampened pupil constriction, and dilation responses compared to CTRL.

Conclusion: RBD and PD patients had altered pupil and blink behavior compared to CTRL. Because RBD saccade parameters were comparable to CTRL, pupil and blink brain areas may be impacted before saccadic control areas, making them potential prodromal PD biomarkers. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Keywords: Parkinson's disease; biomarker; eye movement; prodromal Parkinson's disease.

FIG. 1

(A) Fixation breaks displayed by group during pro‐ (filled) and anti‐ (empty) saccade task. (B) Percent of express saccades during pro‐saccade trials (saccadic reaction time [SRT] >90 ms <140 ms). (C) Median SRTs during the pro (filled) and anti‐ (empty) saccade task. (D) Median amplitude of primary saccades initiated during correct pro‐saccade trials. (E) Percent of direction errors made during the express latency epoch (SRT >90 ms <140 ms) made across groups, and (F) percent of direction errors made during the regular latency epoch (SRT >140 ms) made across groups. One‐way ANOVA with a post hoc Tukey's honest significant difference (HSD) revealed significance between groups *P ≤ 0.05, **P ≤ 0.01, ***P ≤ 0.001. CTRL, healthy, age‐matched controls; RBD, rapid eye movement sleep behavior disorder; PD, Parkinson's disease. [Color figure can be viewed at wileyonlinelibrary.com]

FIG. 2

Mean pupil traces for each patient group are represented during the pro‐ (A) and anti‐ (B) saccade conditions over time. (C) Constriction size was defined as the pupil size at the greatest constriction after fixation appearance. (D) Dilation magnitude was defined as the pupil size at stimulus onset minus the pupil size at the time of greatest constriction during FI, reflecting the increase of pupil size after constriction. (E) Median blink rate during the inter‐trial interval (ITI). *P ≤ 0.05, **P ≤ 0.01, ***P ≤ 0.001. CTRL, healthy, age‐matched controls; RBD, rapid eye movement sleep behavior disorder; PD, Parkinson's disease. [Color figure can be viewed at wileyonlinelibrary.com]