Saccades in internuclear ophthalmoplegia: are abduction disorders related to interocular disconjugacy?

We studied horizontal saccades by direct-current electro-oculography in 18 patients with internuclear ophthalmoplegia (INO), and in 16 healthy, age-matched subjects. The occurrence of abducting signs, i.e. overshoot and dissociated nystagmus, was related to an increase of interocular dissociation (measured by the ratio of abduction and adduction peak velocities). The amplitude of abduction hypermetria was strongly correlated with the intensity of adduction slowing. These findings support the idea of an adaptive mechanism underlying the overshoot and nystagmus of abduction saccades in INO.