Conjugacy of horizontal saccades: application of binocular phase planes.

The goal of this study was to evaluate the ability of binocular phase planes to detect disconjugacy of horizontal saccades. We recorded horizontal saccades in 22 patients with disease affecting the brainstem reticular formation, medial longitudinal fasciculus (INO), abducens nerve, neuromuscular junction and extraocular muscles, and in 10 age-matched controls. We found that patients with disorders of the brainstem, including INO, or the cranial nerves, showed significant velocity disconjugacy in the first 10% of the displacement. Patients with myasthenia gravis did not show early disconjugacy, but might do so later in the course of the saccade. We conclude that binocular phase planes supplement conventional measures of saccades, such as peak velocity, and are useful to differentiate INO and cranial nerve palsies from myasthenia.