Abstract Details

Vestibular compensatory eye movements provide a mechanism to maintain steady fixation on targets during head movement. The anatomic pathways that mediate a normal horizontal vestibulo-ocular reflex (h-VOR), when lesioned, cause spontaneous nystagmus. While the effect of convergence on spontaneous nystagmus has been reported in various populations, the response to adaptation to near targets in patients with peripheral or central vestibular lesions has not been studied.

We aim to clarify potential vestibular and near-reflex interactions by comparing the near and far h-VOR in normal volunteers to patients with unilateral peripheral and central vestibular lesions.

The study consisted of 20 controls, 6 patients with acute unilateral vestibulopathy, and 1 patient with a vestibular nuclear lesion (VNL) in the pontine tegmentum. We examined eye movements, head impulse tests, and convergence in all subjects. H-VOR gain was measured with fixation at 1m (far) and 15cm (near). A repeated measures ANOVA was used for all statistical analyses.

The h-VOR in normal subjects increased with convergence in both eyes (P = 0.027, P < 0.001). In patients with unilateral vestibulopathy, gain failed to increase in either direction (P = 0.25, P = 0.47). No nystagmus with convergence was noted. In contrast, the patient with the left VNL had right horizontal nystagmus when fixating at 15cm and impaired pursuit, which is unchanged over 7 years.

Patients with acute unilateral vestibulopathy did not increase the gain when fixating on a near target; this did not interfere with horizontal nystagmus suppression and did not lead to nystagmus with convergence. Our patient with the hemorrhagic left VNL had normal nystagmus suppression when looking at a distance but failed when viewing a near target. We hypothesize that these findings may be due to selective loss of t-VOR vestibular neurons in the vestibular nucleus, leading to nystagmus and oscillopsia at near distances.