Examining the relationship between a simulated glaucoma impairment and postural threat on quiet stance

BACKGROUND: Vision provides a crucial source of sensory feedback for balance control. Peripheral visual field deficits developed through glaucoma contribute to balance deficits and a fear of falling. Currently, there is no work that examines the direct effect of fear on balance control among glaucoma patients. Therefore, this study aimed to examine the impact of height-induced fear on balance control among healthy individuals exposed to a simulated glaucoma impairment. METHODS: 31 healthy participants stood quietly on a force plate while wearing a virtual reality head-mounted display (HTC Vive) to collect center of pressure (COP) and head displacement (HD) data. Electrodermal activity (EDA) was recorded from the right palm and surface electromyography (EMG) was collected from the right tibialis anterior (TA), medial gastrocnemius (MGast), and soleus (Sol). Trials were 60s, with two at ground level and two at 7 virtual metres above ground, each exposing participants to normal vision and a simulated glaucoma impairment. After each trial, questionnaires were completed to assess balance confidence, fear of falling, perceived stability, and state anxiety. RESULTS: At height, EDA, fear, and anxiety significantly increased, while perceived stability decreased. Anteroposterior (AP) COP sample entropy (SE) and mean power frequency were significantly greater at height with normal vision, while root mean square amplitude increased at height with the glaucoma simulation. AP HD SE was significantly greater at height with normal vision only. Mediolateral COP SE was significantly greater at height for both visual conditions. Lastly, TA activity and TA/SOL co-contraction was greater with normal vision. CONCLUSIONS: Overall, while experiencing height-induced fear with normal vision, participants developed a tighter control of upright stance (increased MPF, SE, TA/Sol activation); however, this was not observed for the simulated glaucoma conditions. Therefore, balance deficits among glaucoma patients may be mediated by fear of falling contributing to a potentially maladaptive strategy.