The Role of Suppression in Amblyopia: A Literature Review

Abstract

Amblyopia is a developmental vision disorder typically treated by occlusion therapy. Recent research suggests suppression is closely linked to deficits in visual acuity and stereopsis, and considerations regarding treatment should include reducing interocular suppression. The aim of this literature review is to provide an analysis of vision science research published within the past 5 years which investigates the role of suppression in amblyopia and discuss the implications to clinical practice. Recent research suggests binocular cells are present in the visual cortex of amblyopes, but are rendered functionally monocular by the development of a GABA inhibitory network. Suppression, or inhibition, can be quantified in both strabismic and anisometropic amblyopia by reducing contrast to the fixating eye until simultaneous perception occurs. In both strabismic and anisometropic amblyopes, higher levels of suppression are associated with lower visual acuities and absent stereopsis. In addition, the evaluation and treatment of suppression is important for the effective treatment of amblyopia, particularly in patients with deep suppression, as they may not respond as well to occlusion therapy. Variable contrast anti-suppression training improves visual acuity, reduces suppression, and improves stereopsis in both children and adults. No age trends were found, which suggests that significant neuroplasticity exists in the adult brain, and suppression may not need to be treated differently in children and adults. Incorporating variable contrast into anti-suppression therapy techniques may enhance treatment progress and promote the development of stereopsis. Existing optometric vision therapy techniques already used to treat suppression are described. Additionally, some of the computer-based tools possess variable contrast stimuli presentation capabilities. Further research is needed to evaluate the optimal length of treatment and long term stability of gains in visual acuity and stereopsis using this treatment strategy.