Disparity vergence responses before versus after repetitive vergence therapy in binocularly normal controls

Abstract

This study sought to determine whether significant changes would be observed between vergence eye movements before and after 12 hr of repetitive vergence therapy (1 hr per day on different days) in subjects with normal binocular vision compared to controls. Disparity vergence responses from 23 subjects were studied. An assessment protocol that minimized the influence of the near dissociated phoria on the disparity vergence system was designed. The following parameters were quantified for the responses: latency, time to peak velocity, settling time, peak velocity, and accuracy (difference between the response and stimulus amplitudes). The following outcomes were observed when comparing the results after vergence therapy to the baseline measurements: (a) near point of convergence and near dissociated phoria did not significantly change (p > 0.15); (b) latency, time to peak velocity, and settling time significantly decreased (p ≤ 0.01); and (c) accuracy significantly improved (p < 0.01). Results support that vergence peak velocity is dependent on the subject's near dissociated phoria. The accuracy and temporal properties of vergence eye movement responses from subjects with normal binocular vision can be improved after vergence therapy. These methods can be utilized within future studies to quantitatively assess vergence therapy techniques for patients with binocular dysfunction.

Figure 1

Experimental setup of haploscope with components labeled (A) and each of the four types of visual stimulus steps (B). “P” denotes the near dissociated phoria level of the subject as assessed using the flashed Maddox rod technique.

Figure 2

Experimental design showing the two main effects of group (control subjects who did not participate in therapy and the subjects who did participate in vergence therapy) and time (baseline and postassessment). Both assessments had test and retest sessions to assess reliability.

Figure 3

(A) Data analysis graphs of convergence position and velocity as a function of time traces. (B) Phase plane plot (i.e., velocity as a function of position).

Figure 4

Group-level analysis of 12 subjects who participated in vergence therapy (blue triangles) and the 11 subjects who were controls and did not participate in vergence therapy (red circles). The means of the latency, time to peak velocity, settling time, and accuracy are plotted.

Figure 5

Average position (solid) and velocity (dotted) vergence eye movement responses before (blue) and after (red) vergence therapy that depicts different responses to the vergence therapy. (A) Average response that was approximately critically damped and did not substantially change after vergence therapy. (B) Average response that was underdamped before vergence therapy and became, on average, more critically damped after vergence therapy. (C) Average response that was overdamped before vergence therapy and then, on average, became more critically damped after vergence therapy. (D) Average response that was overdamped and did not exhibit substantial change after vergence therapy.

Figure 6

Typical average vergence eye movements that show an underdamped (red), an overdamped (blue), and an approximately critically damped (green) vergence response. (A) Position (degrees) as a function of time (seconds) data. (B) Velocity (degrees per second) as a function of position (degrees) also called the phase plane.

Figure 7

Group-level analysis of the response to stimulus target amplitude ratio for the 12 subjects who participated in vergence therapy (A) and the 11 control subjects who did not participate in vergence therapy (B). Histograms represent the average of the four types of the vergence eye movements measured at baseline (blue) and during postassessment (red). An ideal ratio is when the response amplitude equals the visual stimulus or a ratio equal to one.

Figure 8

Linear regression analysis of settling time as a function of accuracy defined as the error between the response amplitude and stimulus amplitude.

Figure 9

Average plus and minus one standard deviation of peak velocities (degrees per second) for the following types of eye movements: convergence from phoria (blue), convergence to phoria (green), divergence from phoria (red), and divergence to phoria (purple).