The Role of Binocularity in Anisometropic Amblyopia

Abstract

Anisometropic amblyopia is unilateral by definition and current treatment recommendations reflect that characteristic. However, recent research suggests a binocular component that deserves consideration. The aim of this review is to consider the levels of anisometropia deemed amblyogenic, and the cortical changes that occur in the presence of anisometropic amblyopia. Particular attention is given to cortical changes that impact the binocularity of these individuals. Knowledge of binocular deficits in anisometropic amblyopia have implications for current, accepted treatment regimens which are monocular in nature. Therefore, the integrity of binocular function in anisometropic amblyopia and its impact on visual outcome will be evaluated. Given the rise in binocular treatments under clinical trial for amblyopia, this review also aims to evaluate the evidence of potentially enhanced benefits to anisometropic amblyopies from proposed new binocular therapies.

Analyses of eye movement parameters in children with anisometropic amblyopia

“…Regardless of positioning accuracy, repositioning is necessary after saccade correction (through overshoot or undershoot). Previous literature regarding cortical damage in amblyopic children [ 16 ] is consistent with a prolonged conduction time that results in increased saccade latency; poor eyesight affects positioning ability, leading to frequent adjustment of the amblyopic eye and increased saccade amplitude. Additionally, saccade latency was significantly longer in children with severe amblyopia than in the other two groups.…”

“…During sensitive periods of visual development, long-term suppression can lead to loss of retinal input and a decline in regulatory function [ 14 , 15 ]. Additionally, anisometropia disrupts binocular vision with increasing severity as the degree of anisometropia increases [ 16 ]. Recent studies regarding children with anisometropic amblyopia have focused on diagnoses that involve static vision.…”

“…Amblyopia is positively correlated with the degree of fixation instability, but normal contralateral eyes in children with anisometropic amblyopia also exhibit fixation instability compared with control eyes. This phenomenon is regarded as “initial signal abnormalities” in contralateral eyes [ 16 ]. Here, we compared the contralateral eyes of children with anisometropic amblyopia (group B) to control eyes (group C); we found that both latency and amplitude were greater in group B than in group C before and after treatment.…”

“…Thus, only an improvement in saccade positioning ability can lead to a reduced amplitude or smaller fluctuations. The abnormal binocular visual function in anisometropic amblyopia may be related to defects in the visual cortex [ 16 ]. In the present study, we found saccadic amplitudes of some participants fluctuated greatly before and after treatment, but no significant differences.…”

Single Center to Evaluate and Compare Anisometropic Amblyopia in Adults Using Blood Oxygenation Level-Dependent Functional Magnetic Resonance Imaging and Diffusion Kurtosis Imaging

“…This indicates that the microstructure complexity of bilateral visual radiation in patients with anisometropic amblyopia may decrease, which may be related to the changes in the density, direction, myelin sheath, and other aspects of the visual radiation fiber. In previous studies [ 16 , 17 ], it was confirmed that the cells of the lateral geniculate body of amblyopia are shrunken and their function is impaired and that optic radiation is composed of fibers emitted after the lateral geniculate body. Therefore, the optic radiation of patients with amblyopia may have dysplasia and abnormal fiber projection, which reduces its complexity.…”