Istradefylline Improves Impaired Smooth Pursuit Eye Movements in Parkinson's Disease

INTRODUCTION

Patients with Parkinson's disease (PD) exhibit alterations in eye movement control, primarily diverse oculomotor deficits which include hypometric saccade and impaired smooth pursuit with reduced pursuit-gain necessitating catch-up saccades. The effects of dopaminergic treatment of PD on eye movements are controversial. Previous studies suggest that smooth pursuit eye movements (SPEMs) are not directly influenced by the dopaminergic system. The nondopaminergic drug istradefylline, a selective adenosine A2A receptor antagonist, reduces the OFF time and improves somatomotor function in levodopa-treated PD. Here, we investigated whether istradefylline improves SPEMs in PD, and determined whether oculomotor performance is associated with somatomotor performance.

METHODS

Using an infrared video eye tracking system, we quantified horizontal SPEMs in six patients with PD before and 4-8 weeks after initiation of istradefylline administration. A further five patients with PD were tested before and after a 4-week interval without istradefylline to control for practice effects. We evaluated smooth pursuit gain (eye velocity/target velocity), accuracy of smooth pursuit velocity, and saccade rate during pursuit before and after istradefylline administration during the ON state.

RESULTS

Patients received istradefylline by single daily oral administration at 20 to 40 mg. Eye tracking data were obtained 4-8 weeks after initiation of istradefylline administration. Istradefylline increased smooth pursuit gain and the accuracy of smooth pursuit velocity, and tended to decrease saccade rates during pursuit.

CONCLUSIONS

Istradefylline ameliorated the oculomotor deficit in SPEM of patients with PD, although differences in somatomotor performance before and after istradefylline treatment were not significant during ON periods. The discrepancy observed between the oculomotor and somatomotor responses to istradefylline supports previous findings that SPEM is at least partially under nondopaminergic control.

Bedside video-oculographic evaluation of eye movements in acute supratentorial stroke patients: A potential biomarker for hemispatial neglect

BACKGROUND AND PURPOSE

The presence of hemispatial neglect adversely affects functional outcomes in stroke patients; consequently, it warrants early targeted rehabilitative intervention. Nevertheless, hemispatial neglect in the acute phase of stroke has often been underdiagnosed. In this study, we aimed to detect hemispatial neglect at the bedside in acute stroke patients by measuring eye movements using video-oculography (VOG).

METHODS

Forty-seven patients with acute unilateral supratentorial stroke were enrolled. We quantitatively measured horizontal saccade (latency, velocity, and amplitude) and smooth pursuit (gain) at the bedside using VOG and compared these variables with scores on the Behavioral Inattention Test (BIT), a screening battery to assess hemispatial neglect.

RESULTS

Contralesional saccade latency, velocity, and amplitude, and ipsilesional smooth pursuit gain were suppressed compared with those in the opposite directions (p = 0.08, 0.02, 0.04, and 0.02, respectively). These directional ocular hypokinesia values correlated with the total BIT score (correlation coefficients -0.53, 0.48, 0.51, and 0.39, respectively). The association was significant even after adjusting for age and stroke severity.

CONCLUSIONS

Eye movement measurements performed using VOG significantly correlated with the tendency for hemispatial neglect in acute supratentorial stroke patients. Bedside VOG measurement may be a simple biomarker for detecting hemispatial neglect even in patients in the supine position during the acute phase of stroke.

Properties of smooth pursuit adaptation induced by theta motion

Current study attempted to determine whether repeated smooth pursuit trials using theta motion, in which the directions of retinal image-motion and object-motion are opposed, yield pursuit adaptation. Adaptation trials consisted of 350 step-ramp trials using theta motion, and pre- and post-trials using first-order motion were conducted. As a result, initial acceleration in post-adaptation increased significantly than pre-adaptation trials. This was the case even though there was no adaptive change throughout adaptation (350 trials) using theta motion. Our results suggest that smooth pursuit could adapt to theta motion even with challenges associated with opposite retinal slip.

Motion direction representation in multivariate electroencephalography activity for smooth pursuit eye movements

Visually-guided smooth pursuit eye movements are composed of initial open-loop and later steady-state periods. Feedforward sensory information dominates the motor behavior during the open-loop pursuit, and a more complex feedback loop regulates the steady-state pursuit. To understand the neural representations of motion direction during open-loop and steady-state smooth pursuits, we recorded electroencephalography (EEG) responses from human observers while they tracked random-dot kinematograms as pursuit targets. We estimated population direction tuning curves from multivariate EEG activity using an inverted encoding model. We found significant direction tuning curves as early as about 60 ms from stimulus onset. Direction tuning responses were generalized to later times during the open-loop smooth pursuit, but they became more dynamic during the later steady-state pursuit. The encoding quality of retinal motion direction information estimated from the early direction tuning curves was predictive of trial-by-trial variation in initial pursuit directions. These results suggest that the movement directions of open-loop smooth pursuit are guided by the representation of the retinal motion present in the multivariate EEG activity.