Dichoptic De-Masking Learning in Adults With Amblyopia and Its Mechanisms

Abstract

Citation: Liu X-Y, Zhang J-Y. Dichoptic de-masking learning in adults with amblyopia and its mechanisms. Invest Ophthalmol Vis Sci. 2019;60:2968-2977. https://doi.org/10.1167 PURPOSE. Recently, we reported that dichoptic de-masking training can further boost stereoacuity, but not visual acuity, in adults with amblyopia after extensive monocular perceptual training. Here, we investigated whether this dichoptic training targets on interocular suppression directly, or improves vision through high-level brain mechanisms.METHODS. Eleven adults with amblyopia first used amblyopic eyes (AEs) to perform contrast (n ¼ 6) or orientation (n ¼ 5) discrimination training, while resisting dichoptic noise masking from fellow eyes (FEs). Learning was indicated by increased maximal tolerable noise contrast (TNC) for AE contrast/orientation discrimination. After dichoptic training, six observers continued to use AEs to perform monocular training for nine sessions. RESULTS.(1) Training of dichoptic de-masking doubled maximal TNC, but learning did not transfer much to the same task at an orthogonal orientation or a different task, showing orientation/task specificities. (2) Following a training-plus-exposure (TPE) protocol, AEs then received exposure of the orthogonal orientation by performing the other orientation/contrast discrimination task at the orthogonal orientation. After this TPE training, dichoptic learning with the original discrimination task transferred to the orthogonal orientation. (3) Dichoptic training improved AE's acuity (1.2 lines), stereoacuity (60.2%), and contrast sensitivity (mainly at higher spatial frequencies). (4) Additional monocular training did not produce further acuity and stereoacuity gains.CONCLUSIONS. The initial orientation/task specificities exclude the possibility that dichoptic training reduces physiological interocular suppression. The later transfer of learning to an orthogonal orientation with TPE training suggests improvement in high-level brain processing. Dichoptic training may strengthen top-down attention to AEs to counter the impacts of attentional bias to FEs and/or physiological interocular suppression and improve stereoacuity.

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

“…Our results about TNC training differed from those of Zhang et al in terms of improvement in stereoacuity, who found a significant (410.9 ± 70.7 to 152.7 ± 35.9 ) improvement in stereoacuity (Liu and Zhang, 2019). Although both studies exploited a similar strategy, the intensity of training was different, with more sessions of training (17 sessions) performed in Zhang et al, likely leading to larger visual improvements (Li R.W.…”

“…On the other hand, there was no significant correlation between all improvements in binocular and monocular vision after HNC training, similar to a previous study (Jia et al, 2018). Zhang et al found that monocular training further reduced the contrast threshold of the amblyopic eye of patients with dichoptic TNC training experience (Liu and Zhang, 2019). Taken together, these results suggested that dichoptic and monocular training have (at least partially) different mechanisms of improving amblyopic vision.…”

“…Second, we performed a retest on five patients 12 months post-training and found robust retention of the training effects (e.g., visual acuity and monocular unmasked CSF) following HNC training. On the contrary, our results suggested that dichoptic and monocular training may involve different mechanisms (e.g., bias the top-down attention toward the amblyopic eye) (Liu and Zhang, 2019). Another limitation for this study is the lack of a reversed crossover, i.e., HNC training followed by TNC training, without which we could not determine the exact interaction of the two training strategies.…”

“…Stereopsis was measured using the Random Dot Stereo Acuity Test (Vision Assessment Corp., Elk Grove Village, IL). For patients who were unable to perceive depth at the 500 arcsec, we designated their stereoacuity as 800 arcsec (Liu and Zhang, 2019). All ophthalmologic examination procedures were conducted in the same clinic room under constant lighting conditions.…”

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

“…To manipulate interocular suppression directly, previously we adopted a different dichoptic demasking training paradigm (detailed provided in Methods and Results), in which the observers were trained to discriminate the contrast or orientation of a Gabor stimulus presented to the amblyopic eyes while resisting dichoptic noise masking from the fellow eyes. 28,29 The amblyopic observers were significantly more capable of discounting dichoptic noise masking after training. Moreover, dichoptic training further improved stereoacuity, but not AE visual acuity, in monocularly well-trained adults with amblyopia.…”