Vergence deficits in patients with cerebellar lesions

Abstract

The cerebellum is part of the cortico-ponto-cerebellar circuit for conjugate eye movements. Recent animal data suggest an additional role of the cerebellum for the control of binocular alignment and disconjugate, i.e. vergence eye movements. The latter is separated into two different components: fast vergence (to step targets) and slow vergence (to ramp and sinusoidal targets). The aim of this study was to investigate whether circumscribed cerebellar lesions affect these dynamic vergence eye movements. Disconjugate fast and slow vergence, conjugate smooth pursuit and saccades were binocularly recorded by a scleral search coil system in 20 patients with acute cerebellar lesions (all ischemic strokes except for one) and 20 age-matched healthy controls. Patients showed impairment of slow vergence while fast vergence was unaffected. Slow vergence gain to sinusoidal targets was significantly reduced, both in convergence and divergence direction. Divergence but not convergence velocity to ramp targets was reduced. Conjugate smooth pursuit eye movements to sinusoidal and to step-ramp targets were impaired. Patients had saccadic hypometria. All defects were particularly expressed in patients with vermis lesions. In contrast to recent animal data fast vergence was not impaired in any of our patient subgroups. We conclude that (i) the human cerebellum, in particular the vermis, is involved in the processing of dynamic vergence eye movements and (ii) cerebellar lesions elicit dissociable effects on fast and slow vergence.

Vergence in mild traumatic brain injury: A pilot study

“…They may be helped by appropriate therapeutic intervention, namely small steps of disparity stimuli, as well as smooth and continuous disparity ramp stimuli (e.g., vectograph ramp stimuli) per models of the vergence system [22,31]. Furthermore, the present abnormal static findings suggest, and are consistent with, disturbance of slow vergence control [32][33][34] (e.g., ramp stimulus for NPC testing). Thus, both fast and slow vergence control appear to be adversely affected by the brain injury.…”

“…This would have provided important information regarding the precise sites of damage to the brain, especially as related to vision and, more specifically, to vergence control, as mentioned previously. However, since all were mTBI, it would be expected to be relatively comprehensive in nature, thus having multiple sites of injury per the coupcountercoup aspect [23] frequently found in these patients, and not be as more localized damage as suggested by the cerebrovascular accident results in this area [32][33][34]. Third, because of the relatively small sample size, definitive conclusions cannot be made; thus, further related investigations are warranted.…”

Recovery of Upper Limb Function After Cerebellar Stroke

“…1 Few studies examined the motor deficits in the acute stage after a cerebellar stroke. In addition to the classical descriptions of acute symptoms after cerebellar injury, 3,5,6 several recent reports have produced a more detailed account about the effects of acute lesions on oculomotor and speech-motor control, 7,8 language function, 9 and wrist motion. 10 However, to our knowledge, there are no objective biomechanical data available regarding how a cerebellar infarction affects multi-joint upper limb function in the acute stage.…”

The cerebellum in eye movement control: nystagmus, coordinate frames and disconjugacy

“…22,27 Vergence itself may also be affected. 28 Experimental lesions in the dorsal vermis of monkeys produce an esodeviation, but no vertical deviation. 29 The cerebellar flocculus has neurons that discharge with vergence, perhaps related to adjusting vestibular responses for near viewing.…”