ABSTRACT
This chapter focuses on tonic and dynamic aspects of torsional eye movement deficits after mesencephalic lesions in patients and monkeys. Patients with midbrain lesions were examined by three-dimensional eye movements recordings, fundus photography and their estimate of the subjective visual vertical. A similar mechanism might be involved in unilateral lesions of the paramedian pontine reticular formation, the generator for conjugate horizontal eye movements, which produce a horizontal spontaneous nystagmus beating in the same direction as the tonic horizontal deviation of the eyes, i.e. to the contralesional side. Rotation of the upper poles of the eyes to the right, i.e. extorsion of the right eye and intorsion of the left eye is defined as positive torsion. Using tundoscopy, clinical studies have shown contraversive tonic binocular torsion of the eyes up to 25 deg after mesencephalic lesions.
