Introduction
Numerous studies have categorized the causes of falling in older adults into two groups: External (e.g. slippery and frictionless surfaces, inadequate lighting in homes and public spaces, inappropriate footwear, and narrow stairs without handrails) and internal (e.g. weakness of the lower limb muscles, slow motor response, weakened vision, and imbalance). Accordingly, impaired balance is one of the primary factors contributing to falls in the elderly. Inadequate ambient lighting also leads to a decrease in functional independence and an increased risk of balance disturbance and falls in the elderly. In addition to physical and physiological factors, psychological factors such as fear of falling are also effective. The fear of falling can lead to motor impairment, reduced daily living activities, and decreased quality of life.
Due to age-related changes in the vestibular and proprioceptive systems, reliance on visual information for maintaining balance and postural control increases with age. However, the impact of aging on the decline in the function of visual and proprioceptive systems is not is not the same; its impact on the visual system is more pronounced. Therefore, considering the important role of vision in maintaining balance in the elderly, one of the effective ways to reduce problems caused by impaired balance in the elderly is the sports vision training (SVT). Since ambient lighting affects individuals’ ability to acquire information from their environment, and considering that age-related changes in the visual system can affect the acquisition of visual information, the use of SVT can play a crucial role in maintaining balance in the elderly by enhancing their visual perception in environments with normal lighting (daylight) and low lighting (nightlight). The present study aims to assess the effect of SVT on the balance and fear of falling in older adults in two environmental conditions with low and normal lighting. 

Methods and Materials
This is a quasi-experimental study with a pre-test/posttest design conducted on 39 older adults aged 65-75 years, who were recruited using a convenience sampling method. The inclusion criteria were a score higher than 24 on the mini-mental state examination (MMSE) which indicated the absence of cognitive impairments, ability to understand verbal instructions, no uncorrected vision, bone fracture, history of diseases such as Parkinson’s disease, multiple sclerosis, and cardiovascular diseases, having a healthy auditory system, no consumption of special drugs, and no need to assistive devices such as walker and cane. They were also asked not to engage in any physically or cognitively demanding activities while participating in this study. The exclusion criteria were unwillingness to continue participation in the study or incidence of any special event hindering them from participation. They were divided into three groups of low light exercise (LLE), normal light exercise (NLE), and control.
After pretest assessments, each experimental group (LLE, NLE) participated at 24 sessions of SVT under different lighting condition, while the control group continued their usual activity during this period. In pre and posttest phases, the berg balance scale test for static balance, timed up & go (TUG) test for functional balance, and the falls efficacy scale-international (FES-I) were used. Statistical analysis was carried out using mixed-method analysis of variance (ANOVA). Pairwise comparisons were performed using the least significant difference (LSD) test, and the effect size was calculated. The significant level was set at 0.05.

Results
The results of repeated measures ANOVA on the static balance (Berg test) under normal lighting condition showed that the main effect of group (F(2, 37)=2.90, P=0.07, η2=0.14) was not significant, but the main effects of time (F(1, 37)=417.39, P<0.001, η2=0.93) and the interaction effect of group and time (F(2, 37)=96.32, P<0.001, η2=0.84) were significant. The results of the paired t-test indicated that the SVT under normal light in both LLE and NLE groups improved the static balance of the elderly, but the percentage of improvement was higher in the NLE  group (29%) compared to the LLE group (18%). 
The results of repeated measures ANOVA on the static balance (Berg test) under low lighting condition showed that the main effect of group (F(2, 37)=2.20, P=0.01, η2=0.10) was not significant, but the main effect of time (F(1, 37)=330.75, P<0.001, η2=0.90) and the interaction effect of group and time (F(2, 37)=78.25, P<0.001, η2=0.81) were significant. The results of the paired t-test indicated that, under low lighting condition, the SVT in both LLE and NLE groups improved static balance in the elderly, but the percentage of improvement was higher in the LLE group (27%) compared to the NLE group (17%). 
The results of repeated measures ANOVA on the functional balance (TUG test) under normal lighting condition showed that the main effect of group (F(2, 37)=0.56, P=0.57, η2=0.03) was not significant, but the main effect of time (F(1, 37)=97.45, P<0.001, η2=0.84) and the interaction effect of group and time (F(2, 37)=97.45, P<0.001, η2=0.84) were significant. The results of the paired t-test indicated that in normal lighting condition, the SVT in both LLE and NLE groups improved the functional balance, but the percentage of improvement was higher in the NLE group (14.5%) compared to the LLE group (4.4%). 
The results of repeated measures ANOVA on the functional balance (TUG) test under low lighting condition showed that the main effect of group (F(2, 37)=0.15, P=0.85, η2=0.73) was not significant, but the main effect of time (F(1, 37)=100.68, P<0.001, η2=0.73) and the interaction effect of group and time (F(2, 37)=18.57, P<0.001, η2=0.50) were significant. The results of the paired t-test indicated that under low lighting condition, the SVT in both LLE and NLE groups improved functional balance, but the percentage of improvement was higher in the LLE group (8.1%) compared to the NLE group (4%). 
The results of repeated measures ANOVA on the fear of falling showed that the main effect of group (F(2, 37) =3.28 P=0.04, η2=0.15), time (F(1, 37)=206.22, P<0.001, η2=0.85) and group×time (F(2, 37)=77.47, P<0.001, η2=0.81) were significant. The results of the paired t-test indicated that the SVT in both LLE and NLE groups reduced the fear of falling in the elderly, but the percentage of reduction was higher in the NLE group (31%) compared to the LLE group (9%). 

Conclusion
The SVT in both LLE and NLE groups can improve the static and functional balance of the elderly. However, its effect in the LLE group is higher than in the NLE group when the balance tests are performed under low lighting condition. Under normal lighting condition, the NLE group show better balance after SVT compared to the LLE  group. Moreover, the SVT can reduce the fear of falling in both LLE and NLE groups, but its effect in the NLE group is greater than in the LLE group. Therefore, to maintain or improve the balance of the elderly, it is recommended that the SVT for older adults be conducted in low-light environments, in addition to considering normal-light conditions. One of the main limitations of this study was the lack of precise measurement of the contribution of each proprioception, vestibular, and visual system. A tool that can measure multisensory integration can be useful for assessing the contribution of these systems to balance control in older adults. 

Ethical Considerations

Compliance with ethical guidelines
This study was approved by the Ethics Committee of Shahid Beheshti University, Tehran, Iran (Code: IR.SBU.REC.1401.097). Informed consent was obtained from all participants. 

Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Authors' contributions
All authors contributed equally to the conception and design of the study, data collection and analysis, interpretation of the results, and drafting of the manuscript. Each author approved the final version of the manuscript for submission.

Conflicts of interest
The authors declare no conflict of interest.

Acknowledgements
The authors would like to thank all participants in this study for their cooperation.



 

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