Standing Balance Stability and the Effects of Light Touch in Adults With Profound Loss of Vision-An Exploratory Study

PURPOSE. We evaluated the postural stability of adults with inherited profound vision loss and examined the effects of touch on their balance control. METHODS. A total of 11 severely-sight impaired patients (mean [SD] age, 51.6 [5.3] years) and 11 control subjects (mean age, 49.7 [5.3] years) participated. Postural stability was measured using a force-balance platform eyes open/ closed on a firm/ foam surface under 3 test conditions: no touch, light touch, and unrestricted touch (UT), where "touch" involved placing their index finger on a rigid table. Average magnitude of center of foot pressure displacement was calculated. A somatosensory ratio (SR) was used to evaluate the somatosensory contribution to balance. A repeated measures ANOVA was used to investigate the effects of touch on standing balance. RESULTS. Patients had a significantly increased SR compared to control subjects (mean [SD] SR controls = 1.2 [0.2], patients = 1.9 [0.5]; P < 0.01). There was a significant effect of touch, vision, and surface on balance control (" touch" F = 68.1, P < 0.01; "vision" F = 20.1, P < 0.01; "surface" F = 200.8, P < 0.01). Light touch attenuated sway in patients and controls. The effects were greater in controls when their vision was removed, and greater in patients when their somatosensory system was disrupted. Light touch was as effective as UT in attenuating sway. CONCLUSIONS. The results of this exploratory study suggest that patients with severe sight impairment show an increased somatosensory contribution to balance control compared to their normally sighted counterparts. Light touch significantly reduces sway amplitude in severely sight impaired adults when standing on the foam surface, that is, when the somatosensory system is perturbed.