The current study was conducted to investigate the dynamic stability of the blind compared to sighted people with their eyes open and closed.

1- Comparing blind and sighted people (while having their eyes open): The highest amount of changes in the parameters related to dynamic stability between the sighted and blind groups were observed in the AP and V axes. In this regard, a significant difference was found among the average factors of speed, range, standard deviation, HR, iHR and RMS in both the AP and V axes, and between sighted and blind people. However, no significant difference was noticed in the ML axis comparing these two groups.

The results of the present study indicated that amongst the investigated variables, the speed of gait in blind people is almost 63% lower than the speed in sighted people. According to the conducted studies, slowing down can be the result of a cautious motor mechanism, which is due to the elimination of the anticipatory mechanism and the lack of environmental input through the visual system [9, 25]. On the other hand, the reduction of gait speed in the absence of vision for maintaining the stability of the body position gives the blind extra time to have a more appropriate and more balanced response, especially through their sense of touch [26]; this can be seen in reducing the standard deviation of the gait pattern of blind people compared to sighted people. In this analysis, the standard deviation of AP and V axes in blind people was 0.10 and 0.12 (g), respectively, and these figures were 0.19 and 0.17 (g) for sighted people.

Based on what is stated in Table 2, the range of accelerometer data in the AP and V axes was 0.82 and 0.77 (g) in the sighted group and 0.45 and 0.56 (g) in the blind group, respectively. Larger values of descriptive data associated with acceleration may reflect a more consistent gait pattern with less range of variation [27]. In this regard, the increase in descriptive parameters related to acceleration in the AP and V axes can indicate an increase in parameters related to balance.

HR and iHR are indices of symmetry, and the reduction of these two indices illustrates the decrease of symmetry and increase of irregularity in steps. The results of the present study showed that in blind people’s group, HR in the AP axis decreased by 0.4% and in the vertical axis by 0.86% compared to sighted people’s group. According to Table 2, the amount of iHR in the AP and V axes was significantly reduced in the group of blind people. The results of this study indicate that the presence of vision results in a more symmetrical performance in steps; according to these findings, irregularity in walking and asymmetry can cause a decrease in dynamic stability and an increase in the probability of falling [4, 5]. In the study conducted by Majlesi et al., the symmetry index was investigated in the parameters of stepping and the comparison of the left and right legs in sighted and blind people, and no significant difference was found between the two groups [10]. The dissimilarity in the results of these two studies may be due to the difference in the indices measured for symmetry.

In this study, the RMS in the AP axis in the sighted and blind groups was calculated as 2.09 and 1.18, and in the V axis, as 1.87 and 1.43. A significant decrease in RMS in blind people can be the result of a decrease in walking speed in these people. Several studies have shown that RMS is affected by walking speed and balance, and has a direct relationship with these factors; and this difference can be seen in all three anatomical axes [10, 28]. In general, the results of this part of the study are in line with the findings of Huijben et al. who worked on a population of elderly people and realized that an increase in walking speed will lead to higher step frequency, higher standard deviation, more symmetrical walking and generally a more stable walking pattern [29].

2- Comparing blind and sighted people (with their eyes closed): A significant difference was seen in the variables of maximum, range, standard deviation and RMS value in the AP axis between the two groups.

The standard deviation of the AP axis was calculated as 0.15 (g) when a sighted person moved with their eyes closed and 0.10 (g) for a blind person. An increase in the standard deviation in the sighted group can indicate a disturbance in the balance and displacement of the body’s center of gravity. Due to having enough time to create a more appropriate response, blind people slow down their walking speed to maintain postural stability and this can be seen in reducing the standard deviation [26].

The maximum variables and the range of accelerometer data in the AP axis were 0.43 and 0.67 (g) in the sighted group while having their eyes closed, and 0.25 and 0.45 (g) in the blind group, respectively. Larger values of descriptive data associated with acceleration could reflect a more consistent walking pattern with less range of variation [27].

Based on the results of this study, no significant difference was found in the walking speed of blind and sighted people with closed eyes. Therefore, the reason for not changing the symmetry may be due to the relative stability of the walking speed.

The root mean square in the AP axis was calculated for sighted people (with their eyes closed) as 1.68, and 1.18 for blind people. This parameter indicates the magnitude of acceleration; and several studies have shown that RMS is affected by walking speed and balance [30]. In this part of the study, RMS showed a meaningful decrease in blind people. In this regard, the authors did not find a study that examines the mentioned variables comparing blind and sighted people with their eyes closed.

3- Comparing the conditions of movement with eyes open and closed in the group of sighted people: Although all the variables decreased while the eyes were closed, a significant difference was found only in the walking speed and the harmonic ratio of the vertical axis.

The walking speed decreased from 1.04 m/s with their eyes open to 0.82 m/s while their eyes were closed. Due to the reliance on visual information, sighted people showed significant changes in movement speed to maintain the walking pattern.

HR in the vertical axis was 2.72% when their eyes were open and 2.15% when their eyes were closed. These results illustrate that in case of deprivation of visual feedback, the symmetry in the vertical axis can be reduced. These changes in sighted people can be due to a lack of adaptation to these conditions. In the study of Iosa et al., only sighted people participated to compare vision effect, and several other parameters such as RMS and HR were utilized to check the stability [4]. The results of this study indicated a decrease in the RMS index in all three axes, and HR only in the AP axis. In Majlesi study, there was no significant difference in speed comparing these two modes [10].

The findings of our study and other studies demonstrate that vision plays a crucial role in the development and maintenance of balance, and balance is reduced because of a lack of vision [31, 32]. Therefore, balance analysis in blind people can help to identify problems related to it, including the state of balance in different axes of the body, to develop strategies to prevent possible events, rehabilitate walking, especially in terms of Orientation and mobility (O&M) training among these people [33].