Altered Fixation-Related Eye-Movement Dynamics in Cervical Dystonia

Cervical dystonia (CD) is characterized by involuntary contractions of the cervical muscles, leading to abnormal head, neck, or shoulder postures. While eye-tracking studies have shown saccadic abnormalities in CD, eye-movement dynamics during fixation remain understudied.

We examined fixation-related eye-movement dynamics during pro- and antisaccade tasks in 35 CD patients and 17 healthy controls, focusing on the 500-1500 ms interval during central fixation. Primary outcomes were maximal binocular angular speed, maximum 30-ms angular-speed variance, and maximal absolute left-right angular-speed difference.

Primary clustered Wilcoxon analyses showed greater peak eye movement speed in CD (p = 0.002), greater short-term variability in speed (p=0.002), and a higher left-right angular-speed difference (p=0.02). These effects remained significant after medication-exclusion sensitivity analysis (p=0.002, p=0.002, and p=0.01, respectively).

Our preliminary findings indicate altered fixation-related eye-movement dynamics in CD and suggest that oculomotor abnormalities in CD may extend beyond saccadic control.