Differences in Smooth Pursuit and Associated Saccades in Children With Two Common Types of Strabismus

The main characteristics of smooth pursuit are well-described, but few studies have analyzed performance in strabismic patients, especially regarding differences between types of strabismus. In this study, we analyzed smooth pursuit eye movements of children with intermittent exotropia (IXT) or accommodative esotropia (AET), compared with age-matched controls.

We included 58 children, aged between 4 and 13 years old (AET n = 24, IXT n = 18, and controls n = 16). After ophthalmological evaluation, eye movements were recorded using a Tobii Pro X3 eye tracker (120 Hz). Smooth pursuit was elicited by a single image moving sinusoidally at the horizontal axis of the screen, with a velocity of 11°/s. Smooth pursuit gain, latency, and frequency of saccades during pursuit, were analyzed.

Smooth pursuit showed different characteristics in the three groups. Gain was significantly lower in IXT, compared with the control group (0.66 vs 0.69; P < 0.01). In contrast, AET patients showed a significantly greater number of anticipatory saccades during pursuit (1.84 [1.46/2.23] vs 0.76 [0.57/0.94]; P = 0.028) compared with controls. No differences were found in latency between the three groups, although we observed faster responses when a saccade occurred (259.2 vs 282.81 ms). A laterality analysis showed better performance for rightward than leftward movements and small differences between nasal and temporal pursuit directions.

Smooth pursuit is affected by strabismus, but performance differs between clinical subtypes. We hypothesized that the smooth pursuit system is primarily affected in IXT, whereas the saccade system might be more affected in AET.