Quantitative measurement of interocular suppression in children with amblyopia

Abstract

Previously it has been shown that intensive training aimed at reducing interocular suppression leads to improvement in amblyopic eye acuity as well as binocular vision in adults with strabismic amblyopia (Hess et al., 2010). In the current study we explored the possibility of using this approach to measure interocular suppression in children with amblyopia. We compared children (8–12 years old) with unilateral anisometropic and/or strabismic amblyopia to age-matched control children with normal visual acuity and no ocular pathology. Visual acuity was measured using the Regan high contrast chart; stereopsis was evaluated using the Randot preschool and the Randot circles test. Motion coherence thresholds for left-right direction discrimination were determined using a binocular global motion stimulus presented with virtual reality goggles (eMagin). The proportion of signal dots among noise dots was varied with a staircase procedure. In dichoptic viewing, high contrast signal dots were presented to the amblyopic eye (one eye of control subjects) while low contrast noise dots were presented to the fellow eye (the other eye of control subjects) at the motion coherence threshold. The contrast of the noise dots was increased until performance reached chance levels. Higher contrast thresholds indicated less interocular suppression. Regardless of their stereo acuity, all children in the amblyopic group exhibited some degree of binocular function on the dichoptic motion task. The amount of interocular suppression was high in the strabismic group and low in the anisometropic group indicating that interocular suppression is more potent in strabismic than in anisometropic amblyopia (Harrad and Hess, 1992). We have shown that the Hess et al stimuli can be used to measure both interocular suppression and residual binocular function in children with amblyopia. Interocular suppression is an established mechanism for visual loss in strabismic amblyopia; our results suggest it is less of a problem in anisometropic amblyopia.