Pathological eye-head coordination in roll: tonic ocular tilt reaction in mesencephalic and medullary lesions

The fundamental pattern of coordinated eye-head roll motion is based upon utricular/saccular as well as vertical canal input, and mediated by the graviceptive pathways from the labyrinths via pontomedullary vestibular nuclei to the rostral midbrain tegmentum. The tonic bilateral graviceptive input stabilizes the eyes and head in the normal upright position. A unilateral lesion causes imbalance in vestibular tone in the roll plane which results in a tonic ipsiversive ocular tilt reaction (OTR). OTR, the triad of ipsilateral head tilt, skew deviation and ocular torsion, occurred as a tonic response (nonparoxysmal) persisting over months to years and was presumed to be due to upper brainstem lesions in 3 patients. Precise localization was limited because of the nature of the lesions. A reversible tonic OTR was seen with acute infarction of the dorsolateral medulla oblongata in 4 out of 11 patients. It may be explained by an ipsilateral lesion of the posterior canal pathways. Transient OTR seems not to be rare in acute Wallenberg's syndrome and ocular torsion in these patients is dysconjugate with predominant excyclotropia of the ipsilateral hypotropic eye. A deviation of the subjective visual vertical in the direction of the spontaneous head tilt--a previously undescribed feature of OTR--was present in all 7 patients and indicates a pathological shift of the internal representation of the gravitational vector. With respect to perception (subjective vertical) it is proposed that the manifest ipsiversive OTR represents a motor compensation of an apparent eye-head tilt contraversive to the lesioned side. Despite the resulting postural imbalance and the conflicting true vertical of the visual surround, the eyes, head and body are continuously adjusted to what the central nervous system erroneously computes as being vertical.