Abstract
Purpose The effects of strabismus surgery on eye movement are not known in detail, as few studies have compared saccade velocities before and after strabismus surgery. In this study, horizontal saccades were recorded using an eye-tracker in patients with only exotropia to compare the peak velocities (PVs), before and after undergoing strabismus surgery of the same type (unilateral resection and recession). Methods Horizontal saccades of monocular vision were recorded using an eye-tracking device in 18 patients with exotropia and 20 normal subjects. All patients were examined using the same method after strabismus surgery. Results The PVs of adduction and abduction in the patients were higher than those in the normal subjects (in dominant eye, P=0.032 for adduction and P=0.049 for abduction; in nondominant eye, P=0.016 for adduction and P=0.037 for abduction). Following the surgery, the PVs of abduction of the surgical eye (nondominant eye) decreased to the level of the normal subjects (P=0.016). However, there were no correlations between changes in the PVs and the extent of surgery (resection and recession). Conclusion Strabismus surgery normalized the patient's increased PV in the operated eye for abduction of horizontal saccade. Not only peripheral (extraocular muscle) but also central sensory-motor mechanisms may be involved in the changes in PV of horizontal saccades, both of which could result from the improvement of the primary eye position.
Highlights
Saccadic eye movements are important for rapid gaze shifting to visual targets. e peak velocity (PV) of saccades is an important parameter for saccade evaluation. e peak velocities (PVs) correlates with the amplitude of saccades, and the normal range of the PV has already been determined [1, 2]. e PV of horizontal saccades reportedly reaches adult values by the age of 4.5 [3]
In a study by Niechwiej-Szwedo et al [11], there was no significant difference in the PV of saccades between binocular viewing and monocular viewing in patients with horizontal strabismus without stereopsis, whereas in normal subjects and strabismus patients with stereopsis, the PV was lower during monocular viewing than during binocular viewing
The present study does not provide direct evidence for this speculation, both peripheral and central sensory-motor mechanisms may be involved in the changes in the PV of horizontal saccades, both of which could result from the improvement of the primary eye position
Summary
Saccadic eye movements are important for rapid gaze shifting to visual targets. e peak velocity (PV) of saccades is an important parameter for saccade evaluation. e PV correlates with the amplitude of saccades, and the normal range of the PV has already been determined [1, 2]. e PV of horizontal saccades reportedly reaches adult values by the age of 4.5 [3]. A previous study has reported no difference in the mean velocity of horizontal saccades between patients with horizontal strabismus and normal subjects [4]. Ey suggested that strabismus surgery improved the velocity of convergence and of divergence [4]. These previous studies have tested the effects of correcting the eye position on conjugate eye movements in mixed subject populations, including different types of strabismus and some operative methods. Horizontal saccades were recorded noninvasively, using an eye tracking system, in patients with only exotropia (XT), before and after undergoing strabismus surgery of the same type (unilateral resection and recession), as well as in normal subjects. To differentiate eye movement directions, the PV of horizontal saccades for adduction and abduction was calculated separately in each subject. e data were compared between the 2 groups (normal subjects vs. presurgical patients) and pairwise compared between the patients pre- and postsurgery
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