A push-pull treatment for strengthening the ‘lazy eye’ in amblyopia

Abstract

Almost all individuals exhibit sensory eye dominance, one neural basis of which is unequal interocular inhibition. Sensory eye dominance can impair binocular functions that depend on both excitatory and inhibitory mechanisms. We developed a 'push-pull' perceptual learning protocol that simultaneously affects the excitatory and inhibitory networks to reduce sensory eye dominance and improve stereopsis in adults with otherwise normal vision. The push-pull protocol provides a promising clinical paradigm for treating the extreme sensory eye dominance in amblyopia ('lazy eye'). The prevailing standard of care does not directly treat sensory eye dominance; instead, selected excitatory functions in the amblyopic eye are stimulated while the strong eye is patched, on the assumption that recovery of the weak eye's excitatory functions rebalances the eyes. Patching the strong eye does not directly address interocular inhibition; in contrast, the push-pull protocol by design excites the weak eye, while completely inhibiting the strong eye's perception to recalibrate the interocular balance of excitatory and inhibitory interactions. Here, we show that three adult amblyopes who trained on the push-pull protocol gained longstanding improvements in interocular balance and stereopsis. Our findings provide a proof-of-concept and evidence that push-pull learning leads to long-term plasticity.

Perceptual training profoundly alters binocular rivalry through both sensory and attentional enhancements

“…Instead of automatically witnessing frequent switches between rival images, trained observers mostly experienced the task-relevant rival image, with individual percepts occasionally remaining stable for tens of seconds. These drastic changes were largely eye-specific, supporting recent findings indicating that attentional training could be an effective therapy for amblyopia (32). Overall, our results highlight the critical role of early visual mechanisms in resolving binocular rivalry conflict, and show that typically modest effects of attention on binocular rivalry dynamics can be expanded through perceptual training.…”

Learning of monocular information facilitates breakthrough to awareness during interocular suppression

“…When participants perform a discriminative task on the perceived target grating, the results reveal that when this protocol was administered for several days, SED was considerably reduced (Xu et al, 2010), indicating that training modified the strengths of the eye-specific neural representations, as well as their contributions to the binocular view. Interestingly, a recent study has shown that this protocol can be used to reduce amblyopia, an extreme and pathological case of SED (Ooi, Su, Natale, & He, 2013).…”

Stereopsis and amblyopia: A mini-review

“…Ooi, Su, Natale, and He (2013) used a different approach – a sensory dominance “push–pull” task, to achieve the same goal (reducing suppression), in three adults with amblyopia. Their push–pull protocol is designed to “excite the weak eye, while completely inhibiting the strong eye's perception to recalibrate the interocular balance of excitatory and inhibitory interactions.” They report improved contrast thresholds and stereopsis in their three subjects; however only one (S2) met our 2-level/160 arc s criterion.…”

“…A good deal of evidence, both physiological and behavioral, suggests that changing the balance of neural excitation and inhibition by either reducing inhibition or boosting excitation may be crucial in recovery of visual functions (Baroncelli et al, 2011; Bavelier et al, 2010; Morishita & Hensch, 2008). All approaches to retraining the amblyopic eye, whether monocular videogame play (Li et al, 2011), perceptual learning (Levi & Li, 2009), the “push–pull” method (Ooi et al, 2013) or dichoptic training (Hess, Babu, et al, 2014; Hess, Thompson, et al, 2014; Knox et al, 2012; Vedamurthy et al, submitted for publication) seek to achieve this altered balance by increasing signal, reducing noise, or modulating attention in the amblyopic eye.…”