Abduction saccadic movement slowed to either side without any limitation in the end position occurred in a patient. This ocular motor abnormality constituted a mirror image of the well-known internuclear ophthalmoplegia of adduction, and therefore, the present case is an internuclear ophthalmoplegia of abduction.
Internuclear ophthalmoplegia of either type demonstrates that a lesion between the center for conjugate gaze and the ocular motor nuclei can impair phasic activity of the eye muscles without reducing their tonic function.