Effects of Unilateral Ocular Motor Nerve Palsies on Smooth Pursuit Eye Movements in Adult Patients

Abstract

Aim: The aim of this study was to investigate the influence of single ocular muscle weakness on smooth pursuit eye movements. Methods: Infrared video recordings of horizontal and vertical eye movements were obtained from 14 adult patients with either unilateral abducens nerve palsy or trochlear nerve palsy. During the recordings, subsequent series of horizontal, vertical and oblique ramp stimuli of 10°/s constant target velocity and ±10° amplitude were presented under monocular viewing conditions. Results: In both forms of ocular nerve palsies, similar changes of pursuit eye movements were observed in the pulling plane of the paretic muscles. The movements of the covered paretic eye showed the lowest amplitude and gain values as well as the lowest numbers of catch-up saccades. The highest amplitude and gain values were calculated from the movements of the covered sound eye. The highest numbers of saccades, however, were produced by the fixating paretic eye. Conclusions: We conclude that the fixating paretic eye compensates for the paresis by raising the pursuit gain and the number of catch-up saccades. In the covered paretic eye, however, monocular adaptation is connected with a symmetric low pursuit gain and a reduced number of saccades in the pulling plane of the paretic muscle.

KEYWORDS:

• Paralytic strabismus
• single eye muscle palsy
• smooth pursuit
• catch-up saccades
• eye movements
• abducens nerve palsy
• trochlear nerve palsy