Oculomotor Disturbances in Patients with Chronic Nonspecific Spinal Pain

There is increasing evidence that the cerebellum has a role in pain processing. The present study investigates whether chronic pain patients, who are likely to have altered pain processing, exhibit signs of subtle cerebellar dysfunction. We used oculomotor tasks to assess dysfunction of the associated neuronal networks, including the cerebellum.

Thirty patients with chronic nonspecific spinal pain and 30 age- and sex-matched controls were enrolled. Using a head-mounted eye tracker (EyeSeeCam), eye movements were quantified during predictable and unpredictable saccade and smooth pursuit tasks in the horizontal plane.

The initial latency and the velocity variability of smooth pursuit were significantly increased in the chronic spinal pain patients compared with controls (initial latency: 198 ± 20 vs 185 ± 11 ms, P < 0.01; slow phase velocity standard deviation: 3.31 ± 1.02 vs 2.70 ± 0.83°/s, P < 0.05). Moreover, the latency of predictable saccades was prolonged in patients (rightward: 161 ± 20 vs 152 ± 12 ms, P < 0.05; leftward: 164 ± 22 vs 153 ± 18 ms, P = 0.05).

Our results show that chronic spinal pain patients display subtle but significant oculomotor changes as compared with healthy controls. Considering the networks involved in the generation of saccades and smooth pursuit, the results would be consistent with a dysfunction of cerebellar regions, especially parts of the cerebellar hemispheres. Alternatively, they could also point toward a dysfunction in the frontal eye field and/or pontine oculomotor nuclei.