Dichoptic Perceptual Training in Children With Amblyopia With or Without Patching History

Xiang-Yun Liu, Yu-Wei Zhang, Feng Gao, Fei Chen, Jun-Yun Zhang, Xiang-Yun Liu, Yu-Wei Zhang, Feng Gao, Fei Chen, Jun-Yun Zhang

Abstract

Purpose: Dichoptic training is becoming a popular tool in amblyopia treatment. Here we investigated the effects of dichoptic demasking training in children with amblyopia who never received patching treatment (NPT group) or were no longer responsive to patching (PT group).

Methods: Fourteen NPT and thirteen PT amblyopes (6-16.5 years; 24 anisometropic, two strabismus, and one mixed) received dichoptic demasking training for 17 to 22 sessions. They used the amblyopic eye (AE) to practice contrast discrimination between a pair of Gabors that were dichoptically masked by a band-filtered noise pattern simultaneously presented in the fellow eye (FE). Dichoptic learning was quantified by the increase of maximal tolerable noise contrast (TNC) for AE contrast discrimination. Computerized visual acuities and contrast sensitivity functions for both eyes and the Randot stereoacuity were measured before and after training.

Results: Training improved maximal TNC by six to eight times in both groups, along with a boost of AE acuities by 0.15 logMAR (P < 0.001) in the NPT group and 0.06 logMAR (P < 0.001) in the PT group. This visual acuity improvement was significantly dependent on the pretraining acuity. Stereoacuity was significantly improved by 41.6% (P = 0.002) in the NPT group and 64.2% (P < 0.001) in the PT group. The stereoacuity gain was correlated to the pretraining interocular acuity difference (r = -0.49, P = 0.010), but not to the interocular acuity difference change (r = -0.28, P = 0.15). Training improved AE contrast sensitivity in the NPT group (P = 0.009) but not the PT group (P = 0.76). Moreover, the learning effects in 12 retested observers were retained for 10 to 24 months.

Conclusions: Dichoptic training can improve, and sometimes even restore, the stereoacuity of amblyopic children, especially those with mild amblyopia (amblyopic VA ≦0.28 logMAR). The dissociation of stereoacuity gain and the interocular acuity difference change suggests that the stereoacuity gain may not result from a reduced interocular suppression in most amblyopes. Rather, the amblyopes may have learned to attend to, or readout, the stimulus information to improve stereopsis.

Conflict of interest statement

Disclosure: X.-Y. Liu, None; Y.-W. Zhang, None; F. Gao, None; F. Chen, None; J.-Y. Zhang, None

Figures

Figure 1.
Figure 1.
(A) A flowchart of the study design. Two groups of observers (NPT and PT) were recruited according to their treatment history. The experiment consisted of pretraining assessment, dichoptic demasking training, and posttraining assessment. (B) Visual function assessment. Top: Single-E and crowded-E acuities test; Middle: A Gabor patch used for contrast sensitivity measurement. Bottom: The Randot Stereo Test. (C) The dichoptic training paradigm of a contrast discrimination task. From top-left to bottom-right: binocular fusion was first achieved with the assistance of two half-crosses. Then a cue was presented for 200 ms to prime AE. A pair of collinear Gabors were then presented to AE for 200 ms, whereas a bandpass noise masker was presented to FE simultaneously. Observers judged which Gabor had higher contrast. AE, amblyopic eye; FE, fellow eye; NPT, never patch-treated; PT, patch-treated.
Figure 2.
Figure 2.
The effects of dichoptic de-masking training on maximal TNC for AE contrast discrimination task. (A) Session by session changes of the mean maximal TNC for AE contrast discrimination in NPT and PT groups. The lines are the best-fitting exponential functions. (B) Comparisons of individual and mean posttraining and pretraining maximal TNCs. The large symbols represent the group means. (C) Mean percent improvement of performance in NPT and PT groups. (D) Dichoptic demasking learning as a function of pretraining maximal TNC. Data are plotted on a logarithmic scale, and a Deming regression line is plotted. (E) Maximal TNC as a function of training sessions for all observers. In each panel, the line is the exponential fit of the data. Error bars = 1 SEM. AE, amblyopic eye; NPT, never patch-treated; PT, patch-treated; TNC, tolerable noise contrast.
Figure 3.
Figure 3.
The impact of dichoptic training on visual acuities. (A) Pretraining and posttraining single-E and crowded E-acuities for NPT AEs and PT AEs. The filled symbols indicate group means. The digits indicate individual observers (see Tables 1 and 2). Because one PT observer (SA13) did not complete the pretraining computerized-E acuity assessment, his/her data were not included here. The mean of the PT group was based on the other 12 observers. (B) Mean acuity improvement of NPT and PT AEs and FEs. We also replotted data from our previous study for comparison. Error bars = 1 SEM. (C) The correlation between AE acuity improvement and pretraining AE acuity. The solid line shows Deming regression for all observers. Three strabismic observers were indicated by the letter “s.” (D) The correlation between the interocular acuity difference reduction and the pretraining interocular acuity difference. The solid line shows Deming regression for all observers. (E) The visual acuity improvement versus dichoptic demasking learning. (F) The visual acuity improvement versus age. AE, amblyopic eye; FE, fellow eye; NPT, never patch-treated; PT, patch-treated.
Figure 4.
Figure 4.
The impact of dichoptic training on stereoacuity. (A) Pretraining and posttraining stereoacuity for NPT and PT groups. The large symbols indicate group means. The digits indicate individual observers (see Tables 1 and 2). The arrows on the y-axis indicate amblyopic observers who failed the Randot Stereo Test (stereoblind). Their stereoacuity was set at 500 arcsec, the lowest score, for data analysis. (B) Mean improvement of stereoacuity. Left: NPT and PT groups in the current study. Right: Replotted NPT and PT data after monocular training in a previous study.Error bars = 1 SEM. (C) The improvement of stereoacuity as a function of the pre-training interocular acuity difference. The line shows a Deming regression fitting. Strabismic observers are indicated by the letter “s.” (D–H) The improvement of stereoacuity against the reduction of interocular acuity difference (D), the improvement of dichoptic demasking training (E), the improvement of visual acuity (F), the pretraining stereoacuity (G), and children age (H). NPT, never patch-treated; PT, patch-treated.
Figure 5.
Figure 5.
The impact of dichoptic training on contrast sensitivity functions. (A, B) The mean contrast sensitivity functions of the AEs and FEs before and after training in NPT (A) and PT (B) groups, along with individual data points. Each curve is the best fitting of a difference-of-Gaussian function. (C) The mean contrast sensitivity functions for AEs and FEs before and after training, with stimulus spatial frequencies normalized by the corresponding cutoff spatial frequencies. (D) The ratios of the pretraining and posttraining normalized contrast sensitivity functions in AEs and FEs. Error bars = 1 SEM. AE, amblyopic eye; FE, fellow eye; NPT, never patch-treated; PT, patch-treated.

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