Negative Fusional Vergence Is Abnormal in Children with Symptomatic Convergence Insufficiency

Abstract

Significance: Deficits of disparity divergence found with objective eye movement recordings may not be apparent with standard clinical measures of negative fusional vergence (NFV) in children with symptomatic convergence insufficiency.

Purpose: This study aimed to determine whether NFV is normal in untreated children with symptomatic convergence insufficiency and whether NFV improves after vergence/accommodative therapy.

Methods: This secondary analysis of NFV measures before and after office-based vergence/accommodative therapy reports changes in (1) objective eye movement recording responses to 4° disparity divergence step stimuli from 12 children with symptomatic convergence insufficiency compared with 10 children with normal binocular vision (NBV) and (2) clinical NFV measures in 580 children successfully treated in three Convergence Insufficiency Treatment Trial studies.

Results: At baseline, the Convergence Insufficiency Treatment Trial cohort's mean NFV break (14.6 ± 4.8Δ) and recovery (10.6 ± 4.2Δ) values were significantly greater (P < .001) than normative values. The post-therapy mean improvements for blur, break, and recovery of 5.2, 7.2, and 1.3Δ, respectively, were statistically significant (P < .0001). Mean pre-therapy responses to 4° disparity divergence step stimuli were worse in the convergence insufficiency group compared with the NBV group for peak velocity (P < .001), time to peak velocity (P = .01), and response amplitude (P < .001). After therapy, the convergence insufficiency group showed statistically significant improvements in mean peak velocity (11.63°/s; 95% confidence interval [CI], 6.6 to 16.62°/s), time to peak velocity (-0.12 seconds; 95% CI, -0.19 to -0.05 seconds), and response amplitude (1.47°; 95% CI, 0.83 to 2.11°), with measures no longer statistically different from the NBV cohort (P > .05).

Conclusions: Despite clinical NFV measurements that seem greater than normal, children with symptomatic convergence insufficiency may have deficient NFV when measured with objective eye movement recordings. Both objective and clinical measures of NFV can be improved with vergence/accommodative therapy.

Figure 1.

Haploscope instrument used to collect objective eye movement recordings.

Figure 2.

Vergence demand (plotted as angular position in degrees) as a function of time (seconds) is depicted by the blue trace, with the latency (orange arrow) and response amplitude (blue bracket) indicated. Vergence velocity (degrees/sec) plotted as a function of time is indicated by the green trace with the peak velocity (green arrow) indicated.

Figure 3.

Distributions of values from the objective measures dataset are summarized in separate boxplots for the participants with normal binocular vision (NBV), the convergence insufficiency participants at baseline (CI - Pre), and the convergence insufficiency participants after office-based vergence/accommodative therapy (CI - Post). (A) displays the data for peak velocity (°/sec), (B) for time to peak velocity (sec), (C) for response amplitude (°), and (D) for latency (sec). In these boxplots, the bottom and top of the box are the first and third quartiles, and the horizontal line within the box is the median. The ‘+’ indicates the mean. Whiskers are drawn to the most extreme data points within the upper or lower edge of the box plus 1.5 times the interquartile range (IQR). Responses outside the range of the whiskers are identified with stars.

Figure 4.

Ensemble of individual disparity divergence eye movements (grey traces) in degrees as a function of time (seconds) for a control participant with normal binocular vision. The average of the divergence responses is shown in red. Deg=degrees; S = seconds.

Figure 5.

Ensemble disparity divergence responses from Participant 1 before (A) and after (B) office-based vergence/accommodative therapy, and from Participant 2 before (C) and after (D) office-based vergence/accommodative therapy. Each gray trace is a single disparity divergence response. The blue trace and the red traces are the mean responses before and after therapy, respectively. Deg=degrees, s = seconds, OBVAT = office-based vergence accommodative therapy.