Abstract
Abstract: :
Objective: To compare horizontal saccade dynamics in patients with unilateral peripheral and central sixth nerve palsies. Methods: Fifteen patients with sixth nerve palsy caused by idiopathic, presumed ischemic, peripheral damage (5 acute, 10 chronic), five patients with central fascicular sixth nerve palsy caused by brainstem lesions (2 acute, 3 chronic), and ten normal subjects were studied using magnetic scleral search coils. Subjects made saccades to a target that stepped from center to 10° right or left position. Serial recordings were made in seven patients with acute palsy (5 peripheral, 2 central). Saccadic velocities were analyzed by amplitude bins. Results: All patients had an incomitant esodeviation with unilateral abduction deficit. Mean abduction deficit was 80% of normal (range = 95 – 60%) in peripheral and 75% of normal (range = 90 – 70%) in central palsy. Acutely, abducting saccades in the paretic eye were slow in both central and peripheral palsies, as anticipated from weakness of the lateral rectus muscle. In chronic state, abducting saccadic velocities in the paretic eye remained reduced in central palsy, but they increased to normal in peripheral palsy for the tested range of excursion. Adducting saccades in the non–paretic eye (field of action of the contralateral yoked medial rectus muscle) were normal in amplitude and velocity in both central and peripheral palsy, acute or chronic. Conclusions: In chronic peripheral palsy, abducting saccadic velocities in the paretic eye become normal, despite persisting, unchanged limited abduction in the five patients tested serially. Adducting saccades are normal in the non–paretic eye. These findings may be due to partial recovery of the peripheral nerve. This allows both eyes to reach a target in the paretic hemifield of motion rapidly and simultaneously. Abducting saccadic velocities are reduced in acute and chronic central palsy, indicating that recovery or adaptation occurs predominantly in patients with peripheral nerve damage.
Keywords: eye movements: saccades and pursuits • strabismus • ocular motor control