A New Dichoptic Training Strategy Leads to Better Cooperation Between the Two Eyes in Amblyopia

Zitian Liu, Zidong Chen, Le Gao, Manli Liu, Yiru Huang, Lei Feng, Junpeng Yuan, Daming Deng, Chang-Bing Huang, Minbin Yu, Zitian Liu, Zidong Chen, Le Gao, Manli Liu, Yiru Huang, Lei Feng, Junpeng Yuan, Daming Deng, Chang-Bing Huang, Minbin Yu

Abstract

Recent clinical trials failed to endorse dichoptic training for amblyopia treatment. Here, we proposed an alternative training strategy that focused on reducing signal threshold contrast in the amblyopic eye under a constant and high noise contrast in the fellow eye (HNC), and compared it to a typical dichoptic strategy that aimed at increasing the tolerable noise contrast in the fellow eye (i.e., TNC strategy). We recruited 16 patients with amblyopia and divided them into two groups. Eight patients in Group 1 received the HNC training, while the other eight patients in Group 2 performed the TNC training first (Phase 1) and then crossed over to the HNC training (Phase 2). We measured contrast sensitivity functions (CSFs) separately in the amblyopic and fellow eyes when the untested eye viewed mean luminance (monocularly unmasked) or noise stimuli (dichoptically masked) before and after training at a particular frequency. The area under the log contrast sensitivity function (AULCSF) of masked and unmasked conditions, and dichoptic gain (the ratio of AULCSF of masked to unmasked condition) were calculated for each eye. We found that both dichoptic training paradigms substantially improved masked CSF, dichoptic gain, and visual acuity in the amblyopic eye. As opposed to the TNC paradigm, the HNC training produced stronger effects on masked CSFs, stereoacuity, dichoptic gain, and visual acuity in the amblyopic eye. Interestingly, the second-phase HNC training in Group 2 also induced further improvement in the masked contrast sensitivity and AULCSF in the amblyopic eye. We concluded that the HNC training strategy was more effective than the TNC training paradigm. Future design for dichoptic training should not only focus on increasing the tolerable noise contrast in the fellow eye but should also "nurture" the amblyopic eye under normal binocular viewing conditions and sustained interocular suppression.

Keywords: amblyopia; contrast sensitivity functions; dichoptic masking; dichoptic training; interocular suppression.

Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Copyright © 2020 Liu, Chen, Gao, Liu, Huang, Feng, Yuan, Deng, Huang and Yu.

Figures

FIGURE 1
FIGURE 1
(A) Two strategies of dichoptic training used in this study. Left: High noise contrast (HNC) protocol; Sinusoidal gratings were presented to one eye, while a mean background luminance (monocular unmasked condition) or a Gaussian white noise mask (dichoptic masked condition) was presented to the untested eye. From top to bottom: the contrast of gratings in an amblyopic eye (AE) was manipulated from high to low, while noise mask in a fellow eye (FE) was fixed at high contrast (σ = 0.33). With training, the contrast of grating was adjusted (usually decreased) to maintain stable performance. Right: tolerable noise contrast (TNC) protocol; grating contrast in AE was fixed while mask contrast in FE was manipulated from low to high to maintain stable performance. (B) Four conditions of CSFs were measured: unmasked fellow eye (FEU), unmasked amblyopic eye (AEU), masked fellow eye (FEM), and masked amblyopic eye (AEM).
FIGURE 2
FIGURE 2
Learning curves for the two different training protocols in amblyopic participants from (A) Group 1 with constant and high noise contrast in the fellow eye (HNC), (B) Group 2 (Phase 1) with progressively elevated noise contrast in the fellow eye (TNC); (C) Group 2 (Phase 2), HNC training.
FIGURE 3
FIGURE 3
(A) Pre- and post-training contrast sensitivity functions (CSFs) under different conditions in Group 1. (B) Dichoptic gains for the two eyes before HNC training (x-axis) are plotted against those after training (y-axis). The diagonal unity line represents unchanged dichoptic gain between pre- and post-training assessment.
FIGURE 4
FIGURE 4
(A) CSFs under different conditions in Group 2 before (Pre, circle) and after (Post, triangle) the TNC training (Phase 1). (B) CSFs under different conditions in Group 2 after the TNC training (Post, triangle) and after crossed over to the HNC training (Cross, square) (Phase 2). (C) Dichoptic gains for the two eyes in Group 2 before training (x-axis) is plotted against those after training (y-axis) for the two phases. The diagonal unity line represents unchanged dichoptic gain between pre- and post-training assessment.
FIGURE 5
FIGURE 5
Improvements in visual function after HNC vs. TNC training. Error bars represent SEM. *p < 0.05; **p < 0.01; ***p < 0.001.
FIGURE 6
FIGURE 6
Summary of training effects. Groups were represented by different colors: black (Group 1), dark gray (Group 2, Phase 1), and light gray (Group 2, Phase 2). Error bars represent SEM. *p < 0.05.

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