Table 1
Subject Enrollment
| Essential Tremor (n = 60) | Controls (n = 60) | |
|---|---|---|
| Age (years) | 63.4±12.9 | 65.3±7.4 |
| Duration of symptoms (years) | 11.3±13.7 | – |
| Gender: number of males (%) | n = 48 (80%) | n = 40 (66.6%) |
| Postural tremor score | 1.9±0.9 | – |
| Square wave jerks per minute | 26.9±20.01 | 8.4±8.3 |
| Saccadic latency (ms) | 255.3±80.91 | 220.8±46.4 |
| Q-ratio of saccades (peak/mean velocity) | 2.37±2.651 | 1.81±0.39 |
Figure 1
Frequency of Square Wave Jerks while Fixating.
Essential tremor patients exhibit appreciably more square wave jerks than age matched controls (p<0.0001). Middle bars inside boxes represent sample means, while the edges of boxes indicate first and third quartiles. Bottom and top bars represent minimum and maximum, respectively. Circles denote statistical outliers.
Figure 2
Latency of Reflexive Saccades to Randomly Displaced Targets
Patients with essential tremor have increased saccadic latencies compared with age-matched controls (p<0.01).
Figure 3
Velocity profiles of 10° saccades. Single velocity traces are shown for 18 representative essential tremor (ET) subjects and 18 control subjects.
The velocity profiles were aligned at t = 10 ms at the defined saccadic onset threshold (20°/second). Note the lower peak velocity, velocity plateau, and prolonged duration of saccades in ET subjects. The integral was taken of each individual velocity curve, and no difference was found between each group (p = 0.59). This further supports that despite abnormal velocity behavior during saccadic flight, that subjects with ET maintain accurate saccadic amplitudes, and reach the intended target position.
Figure 4
Saccadic Dynamics along the Main Sequence.
(A) Peak velocity vs. amplitude of saccades. For all movement amplitudes, subjects with essential tremor generally exhibit lower peak velocities than controls (Vmax = 400°/second for essential tremor [ET] subjects vs. 500°/second for controls, C = 19.9 for ET subjects vs. 9.1 for controls). (B) Saccadic duration vs. amplitude. Saccades are generally slower for subjects with ET compared to controls, with the group differences becoming progressively greater with increasing saccadic amplitude (average duration of a one degree saccade (D1) = 28.8 ms for ET subjects vs. 20.6 ms for controls, exponential value (n) for ET subjects = 0.41 vs. 0.39 for controls).