Benefits from Vergence Rehabilitation: Evidence for Improvement of Reading Saccades and Fixations

Abstract

We hypothesize that binocular coordination of saccades is based on continuous neuroplasticity involving interactions of saccades and vergence. To test this hypothesis we study reading saccades in young students who were diagnosed for vergence disorders before and after vergence rehabilitation. Following orthoptic evaluation and symptomatology screening, 5 weekly sessions of vergence rehabilitation were applied with the REMOBI vergence double step protocole (see Kapoula et al., 2016). Using the Eyeseecam videoculography device we measured vergence as well as saccades and fixations during a reading test four times: at the beginning and at the end of the first and of the fifth vergence rehabilitation session. The results show elimination of symptoms, improvement of clinical orthoptic scores, and importantly increase of measured vergence gain and reduction of inter-trial variability. Improvement of the vergence was associated to a decrease of the disconjugacy of saccades during reading but also to shortening of fixation durations, to reduction of the number of regressive saccades and to a better correction of the intra-saccadic disconjugacy during the following fixation. The results corroborate the hypothesis of neuroplasticity based on saccade vergence interaction in young adults. It validates the clinical validity of the vergence double-step REMOBI method as a means to improve both, vergence and reading performances. It opens a new research approach on the link between fine binocular coordination of saccades, quality of the vergence response, attention, cognition and reading.

Keywords: cognition; fixation; reading saccades; rehabilitation; vergence eye movements.

Figure 1

Testing chronology: positioning of each test during the first and the fifth vergence rehabilitation session.

Figure 2

Testing protocol: the reading test and the vergence test using the REMOBI, accomplished before and after the first and the fifth session of vergence rehabilitation, and the convergence and divergence rehabilitation using the REMOBI and the double step vergence protocol, accomplished at every session of rehabilitation.

Figure 3

(A) Analysis and marking of the reading saccades: determination of the saccade and of the fixation duration. i and p indicate respectively the beginning and the end of each saccade. We studied the post-saccadic drift 80 and 160 ms after the end of the saccade, x and y indicate respectively these two periods of fixation. Lower trace: horizontal conjugate position. Upper trace: horizontal disconjugate position. (B) Evolution of the conjugate and the disconjugate position of the eyes over time when reading an entire line (subject 2). Lower trace: horizontal conjugate position. Upper trace: horizontal disconjugate position.

Figure 4

Vergence test: disconjugate signal (subject 2) during the vergence test before the first session of rehabilitation and before the fifth session of rehabilitation. i and p indicate respectively the onset and the offset of the vergence movement of the sample colored in black, the time point when the eye velocity exceeded or dropped below 5°/s. Superposition of each convergence or divergence trial is shown in gray.

Figure 5

Scatter plot of the mean gain values ((summation of the gain in convergence and divergence)/2) in the first vergence test of the first and the fifth session of rehabilitation as a function of the CISS score. Black plots represent the gain values in the first vergence test of the first session as a function of the CISS score prior to rehabilitation. Gray plots represent the gain values in the first vergence test of the fifth session as a function of the CISS score after the vergence rehabilitation.

Figure 6

Mean amplitude, SD and number of progressive and regressive saccades: in light-gray, the mean value and the standard deviation concerning the amplitude of the progressive reading saccades; in dark-gray, the mean value and the standard deviation concerning the amplitude of the regressive saccades. Numbers on each column indicate the number of saccade in each reading trial next to each bar.

Figure 7

Saccade disconjugacy in progressive and regressive reading saccades: in light-gray, the mean amplitude and standard deviation concerning the positive saccade disconjugacy; in dark-gray, the mean amplitude and standard deviation concerning the negative saccade disconjugacy. Percentage of positive and negative saccade disconjugacy is indicated for each reading trial next to each bar.

Figure 8

Linear regression plot of the amplitude of saccade disconjugacy in degrees (°) as a function of the amplitude of the following post-saccadic disconjugacy drift in degrees (°) measured 80 ms after the end of each progressive reading saccade. The entire sample has been plotted for each reading trial. Spearman r_s correlation coefficient and p-values are indicated.

Figure 9

Linear regression plot of the mean values of the amplitude of saccade disconjugacy in degrees (°, light gray marks) and of the mean values of the fixation duration in milliseconds (ms, black marks) as a function of the global time of reading in seconds (s). The individual mean values have been plotted for each reading trial and trend lines have been added for each variable.