Attentional Factors Underlying Binocular Vision Loss in Amblyopia

Abstract

Amblyopia is a neurodevelopmental disorder of vision that results from abnormal visual experience during early development. In addition to significant vision loss in one eye, individuals with amblyopia experience binocular dysfunction, difficulty with visuomotor coordination and attentional deficits. A key component of the vision loss associated with amblyopia is strong, chronic suppression of the amblyopic eye. Clinically, suppression remains challenging to treat, and is a key obstacle to rehabilitating visual function in amblyopia. This thesis examines whether suppressed visual information from the amblyopic eye remains available for processing within the brain and whether higher-order attentional processing is affected in amblyopia. Emerging evidence suggests that attentional mechanisms may contribute to interocular suppression and vision loss in amblyopia. Across four experiments, the findings from this thesis provide several major insights about amblyopia. Visual information seen only by a suppressed amblyopic eye retains a presence within the brain that may subsequently be used for attentional processing. Attentional mechanisms in amblyopia were found to be intact to some extent and thus can be engaged. Orienting visual attention was effective for targets seen by a partially suppressed amblyopic eye and even for complex face cues. Selective attentional tracking by the amblyopic eye was intact in anisometropic amblyopia but was impaired for strabismic amblyopia. Additionally, the process of attentional disengagement and re-engagement may be impaired during amblyopic eye viewing. Overall, these results demonstrate that the amblyopic eye continues to influence visual perception despite being suppressed under normal viewing conditions. As a result, appropriate refractive correction of the amblyopic eye should be clinically prescribed to optimize image quality for binocular combination. Furthermore, amblyopia may affect how visual attention is allocated between the eyes, providing a therapeutic target to guide future rehabilitative efforts.