Evaluation of Saccadic and Smooth Pursuit Eye Movements at an Early Stage of Essential Tremor
Objectives: Though still unclear cerebellar involvement is accepted as the underlying pathophysiological mechanism of at least advanced stages of essential tremor (ET). Eye movement abnormalities supporting this hypothesis have been reported. We tried to investigate saccadic and pursuit eye movements in ET patients at an early stage of the disease (mean disease duration 20.35 ± 10.51 months).
Materials and Methods: Binocular horizontal saccadic and pursuit eye movements were recorded by using a video-based eye tracker in 25 patients with ET and 16 age matched controls. For the saccades peak saccadic velocity, latency and accuracy and for pursuit eye movements gain at three different target velocities (0.1, 0.2 and 0.4 Hz) was taken into consideration.
Results: Peak saccadic latency, velocity and accuracy values recorded from the patients during saccadic eye movements were compared with the values gathered from the healthy controls revealing no significant difference (p>0.05). The same was true for pursuit eye movements. Pursuit gain at three different target velocities recorded from ET patients were not statistically different from the healthy controls (p>0.05).
Conclusion: Normal eye movements at the early stage of the disease may indicate cerebellar dysfunction to be a late feature of ET. The other explanation can be the heterogeneous nature of the disease, those with abnormal eye findings representing a specific pathological subset.