Effect of blindfolding on centre of pressure variables in healthy horses during quiet standing.

In a standing horse the centre of pressure (COP), measured as the resultant vertical ground reaction force (GRF) of all supporting limbs, is adjusted in response to visual, vestibular and proprioceptive information. Stabilographic analysis measures balance by tracking COP movements in the horizontal plane. Loss of visual input affects stability of balance in people and has clinical implications in that instability inherent in some neurological diseases increases with the eyes closed. The objectives of this study were to evaluate the visual contribution to postural stability in horses. The hypothesis was that the magnitude and variability of postural sway variables increases when visual input is removed. Vertical GRFs were measured using two synchronized force plates and COP movements were tracked in 20 horses as they stood without visible movements of the hooves, head or neck. Three trials of 60 s duration were recorded under sighted and blindfolded conditions. Stabilographic variables (craniocaudal and mediolateral COP amplitudes, velocities and mean power frequencies and their within-trial variabilities) were calculated and compared using univariate analysis of variance. Compared with the sighted condition, blindfolding increased the magnitude and the within-trial variability of craniocaudal and mediolateral COP amplitudes and mediolateral COP velocity. The findings indicated that loss of visual input had more effect on the measured COP variables in the time domain (amplitudes, velocities) than in the frequency domain (mean power frequency). The effects of blindfolding on postural stability should be further investigated as part of a diagnostic approach to the evaluation of balance in horses with neurological impairment.