The vergence-mediated gain increase: Physiology and clinical relevance

BACKGROUND: During near-viewing, the vestibulo-ocular reflex (VOR) response/gain increases to compensate for the relatively larger translation of the eyes with respect to the target.

OBJECTIVE: To review vergence-mediated gain increase (VMGI) testing methods stimuli and responses (latency and amplitude), peripheral/central pathways and clinical relevance.

METHODS: The authors discuss publications listed in PUBMED since 1980 in the light of their own studies.

RESULTS: The VMGI can be measured during rotational, linear and combined head accelerations. It has short-latency, non-compensatory amplitude, and relies on irregularly discharging peripheral afferents and their pathways. It is driven by a combination of perception, visual-context and internal modelling.

CONCLUSIONS: Currently, there are technical barriers that hinder VMGI measurement in the clinic. However, the VMGI may have diagnostic value, especially with regards to measuring otolith function. The VMGI also may have potential value in rehabilitation by providing insight about a patient's lesion and how to best tailor a rehabilitation program for them, that potentially includes VOR adaptation training during near-viewing.