Visuomotor Behaviour in Amblyopia: Deficits and Compensatory Adaptations

Abstract

Amblyopia is a neurodevelopmental visual disorder arising from decorrelated binocular experience during the critical periods of development. The hallmark of amblyopia is reduced visual acuity and impairment in binocular vision. The consequences of amblyopia on various sensory and perceptual functions have been studied extensively over the past 50 years. Historically, relatively fewer studies examined the impact of amblyopia on visuomotor behaviours; however, research in this area has flourished over the past 10 years. Therefore, the aim of this review paper is to provide a comprehensive review of current knowledge about the effects of amblyopia on eye movements, upper limb reaching and grasping movements, as well as balance and gait. Accumulating evidence indicates that amblyopia is associated with considerable deficits in visuomotor behaviour during amblyopic eye viewing, as well as adaptations in behaviour during binocular and fellow eye viewing in adults and children. Importantly, due to amblyopia heterogeneity, visuomotor development in children and motor skill performance in adults may be significantly influenced by the etiology and clinical features, such as visual acuity and stereoacuity. Studies with larger cohorts of children and adults are needed to disentangle the unique contribution of these clinical characteristics to the development and performance of visuomotor behaviours.

Attention in visually typical and amblyopic children

“…It is also important to note that this pattern is not seen in anisometropic amblyopic adults, who showed no particular elevation of reaction times with the amblyopic eye viewing (Niechwiej-Szwedo et al, 2011), so it is unclear whether in this case the strabismus was the more relevant factor. On the other hand, Hamasaki and Flynn (1981) found a significant interocular difference in reaction time for strabismic amblyopes that was not evident in strabismic nonamblyopes (see also Niechwiej-Szwedo et al, 2019). Our group of children consisted of a greater number of anisometropic than strabismic amblyopes, which may have contributed to the outcome.…”

“…Interestingly, during a covert attention task, visually typical participants tend to make microsaccades (small eye movements) toward the cued location ( Hafed & Clark, 2002 ). The pattern of fixation eye movements in amblyopic and visually typical observers has been found to be different when viewing with the amblyopic eye; mainly, fixation stability is poorer ( Chung et al., 2015 ; Gonzalez et al., 2012 ; see Niechwiej-Szwedo et al., 2019 , for review). But there is no clear consensus from analyses of microsaccades as to the precise pattern of differences between the eyes of amblyopes during simple fixation.…”

Concurrent maturation of visuomotor skills and motion perception in typically‐developing children and adolescents

“…On the other hand, many children with neurodevelopmental disorders also have impairments in motor skill performance (Elliott et al, ); however, it is unclear whether the deficits in motion perception and in motor performance are associated with each other. Additionally, although amblyopia has been shown to disrupt visuomotor skills (reviewed in Grant & Moseley, ; Niechwiej‐Szwedo, Colpa, & Wong, ), and MD form perception (Giaschi, Regan, Kraft, & Hong, ; Wang, Ho, & Giaschi, ) in separate studies, it remains to be established whether it is appropriate to use the latter task as a global index of dorsal stream function. Deficits in MD form perception have been attributed to the dorsal stream (Jakobson, Frisk, & Downie, ), the ventral stream (Guzzetta et al, ) or connections between streams (Regan, Giaschi, Sharpe, & Hong, ).…”

Impact of Amblyopia on the Central Nervous System

“…Some studies have even reported a negative impact on reading. [17][18][19] Effects are not exclusive to the amblyopic eye. The non-amblyopic (fellow) eye actively suppresses input from the amblyopic eye, 20,21 and there are measurable deficits of spatial, position, and motion sensitivity in the fellow eye.…”

“…Delayed saccades, absence of smooth pursuits, and inaccurate vergence movement has been reported in both amblyopic eyes and their non-amblyopic fellow eyes. 17,22 Amblyopic eyes have poor fixation stability, but their fellow nonamblyopic eyes seem to retain this ability. 22,59,60 Accommodation is also less accurate in amblyopic eyes than their fellow eyes.…”