Resumo

The postural control is a complex motor task. Visual, vestibular, and somatosensory inputs are centrally integrated in order to maintain postural stability. The aim of this study was to evaluate how total visual loss affects balance. Our sample was composed by totally blind subjects (n=38; mean±SD; 167.72 ± 13.46 cm; 70.92 ± 14.39 Kg; 28.71 ± 5.47 years) as well as similar age and sex paired sighted subjects (n=32; 168.85 ± 29.61 cm; 77.30 ± 12.49 Kg; 23 ± 5.37 years). To estimate body balance, subjects were asked to stand up on a force platform (AMTI, USA), in a natural position (barefoot, head facing forward and arms along the body), in four different conditions: (1) feet apart and eyes open (AO), (2) feet apart and eyes closed (AC), (3) feet together and eyes open (TO), (4) feet together and eyes closed (TC) during 60 seconds each. All conditions were randomized across trials. Stabilometric signals were sampled at 50 Hz, using an anti-aliasing filter with a cut-off frequency of 5 Hz. The pattern of body sway was determined based in the following stabilometric parameters: area of displacement, standard deviation (SD) and mean frequency (MF) in lateral (ml) and anterior-posterior (ap) directions in each condition. Statistical analysis was performed using ANOVA repeated measures, with groups (blind and sighted) as the between-subjects factor and feet position (apart or together) and visual condition (open or close) as the within-subjects. Planned Comparisons were used when F was significant. ANOVA for SDap and MFap showed a main effect for group (F(1, 68)=7.19; p=0.009 - F(1, 68)=21.76; p=0.00001, respectively), and a significant interaction between feet position x visual condition x group (F(1, 68)=4.15; p=0.04 - F(1, 68)=8.35; p=0.005, respectively). There was no main effect for group for the area of displacement parameter, suggesting a similar global postural outcome in blind and sighted subjects. Planned Comparisons for SDap showed that the sighted group exhibited higher values in AC and TC than the blind group (p<0.03). This difference was absent in AO and TO (p>0.4). These results indicated that the blind group has the same postural behavior than sighted group when it comes to the open eye condition. However, higher values of MFap were found for the blind as compared to the sighted group in AO, AC and TO conditions (p<0.0001), suggesting the use of a different postural strategy between groups in order to maintain stability in the standing position. In conclusion, permanent total visual loss can be compensated by changes in postural strategy.