Binocular coordination of saccades during reading in children with clinically assessed poor vergence capabilities

Prior studies have pointed toward a link between the saccadic and vergence systems, coordinating binocular saccadic movements. Recent studies have shown that vergence deficits in children induce poor binocular coordination during saccades, but none of them have studied ocular motility in children during a daily task such as reading. The present study tests whether vergence deficits in children perturb binocular coordination of saccades and fixation during reading. Our second objective was to explore whether vergence training could improve the quality of binocular coordination. Twelve patients (from 7.3 to 13.4 years old) complaining from vertigo but without vestibular and neurological pathology underwent orthoptic tests and were selected for our study when they presented vergence deficits. Eye movements were recorded during a reading task with a Mobile EyeBrain® Tracker video-oculography system. Data were compared to twelve age-matched controls with normal orthoptic values. While there was no statistically significant difference in saccade amplitudes between the two groups (p=0.29), patients showed higher disconjugacy during and after the saccades compared to controls (p<0.001). After orthoptic training, six patients out of the first 12 examined came back for a second oculomotor test. All showed a significant improvement of their binocular saccade coordination. We suggest that the larger disconjugacy during reading observed in patients before training could be due to poor vergence as initially assessed by orthoptic examination. Such findings support the hypothesis of a tight relationship between the saccadic and vergence systems for controlling the binocular coordination of saccades. The improvement reported after orthoptic training is in line with the hypothesis of an adaptative interaction on a premotor level between the saccadic and vergence system.