Objective: To study eye movements by video-oculography (VOG) in ET patients, and to evaluate the possible relationship between oculomotor abnormalities and the hereditary character of ET and age of onset.

Background: Essential tremor (ET) is the most common movement disorder in adults. ET is defined by the MDS Consensus Statement on Tremor as isolated action tremor of bilateral upper limb with or without tremor in other locations and without other neurological signs. However, there is increasing evidence in favor of a variable clinical phenotype. Classically, ET is considered as a manifestation of a deficit of the cerebellum and its connections although pathological patterns observed in ET are not homogenous. ET may be not a single disease but rather a syndrome. Only a few studies reported on oculomotor abnormalities in ET showing conflicting data.

Methods: VOG was performed in consecutive patients with ET. Eye movements were recorded using the Mobile EyeBrain Tracker. We tested for horizontal and vertical reflex saccades and smooth pursuit. ET patients were separated in three groups: hereditary ET with age onset before or after 65 y (group 1), sporadic ET with age onset before 65 y (group 2), and sporadic ET with onset after 65 y (group 3). Fisher exact test was used to compare sporadic early onset (group 2) vs late onset (group 3), hereditary (group 1) vs sporadic (group 2+3), and each group.

Results: Fifty ET patients were enrolled into the study: 30 patients (60%) in group 1, 14 patients (28%) in group 2, and 6 (12%) in group 3. In the three groups the more frequent abnormalities were saccadic intrusions (70% in group 1, 50% in group 2 and 83% in group 3), vertical saccade hypometria (37%, 43%, 83% respectively in the group 1, 2 and 3) and saccadic smooth pursuit (37%, 43% and 50%.) Slow downward vertical saccades were observed in 30%, 28% and 83% and increased latency of horizontal saccades in 13%, 7% and 17%. A significant trend was seen between early and late onset patients: late onset patients showing more frequently slow downward vertical saccades (p=0.04).

Conclusions: Eye movement abnormalities detected by VOG are common in ET. Late onset ET showing more frequently slow downward vertical saccades than early onset ET patients. The other characteristics are not related to clinical phenotype.

References: Deuschl G, Elble R. Essential tremor – neurodegenerative or nondegenerative disease towards a working definition of ET. Mov Disord 2009;24(14):2033–41. Slowed Saccades and Increased Square Wave Jerks in Essential Tremor. George T. Gitchel, Paul A. Wetzel, Mark S. Baron Tremor and Other Hyperkinetic Movements.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/study-of-eye-movements-by-video-oculography-in-essential-tremors/