This study examined the association between sleep duration and VI in a nationally representative sample of older adults in China. Using large-scale population-based data, this study reached several findings. First, self-reported VI was highly prevalent among middle-aged and elderly adults in China. Second, short (≤ 6 h/night) and long (> 8 h/night) sleep durations were significantly associated with VI risks after adjusting for internal and external factors. In addition, we found a stronger association between VI and self-reported short and long sleep durations in middle age (≥ 45 and ≤ 58 years) respondents than the elderly. Our findings suggest that both short and long sleep durations could be a predictor of VI.
The prevalence of VI in China was demonstrated to be higher than that in the US or Asia [23]. The rapidly aging Chinese population may account for it. Chen et al.[24] reported that cataracts were the leading cause of bilateral or monocular VI among adults 50 years and older in the Binhu District of Wuxi City, China, followed by high myopic macular degeneration, age-related macular degeneration, and eye loss/atrophy. Bourne et al.[25] reported that leading causes worldwide were cataracts for blindness and uncorrected refractive error for moderate and severe VI. Moreover, more women were blind or having moderate and severe VI than men due to cataracts and macular degeneration worldwide and in all regions [25]. Our results revealed that the prevalence of VI in women was higher than that in men in the elderly (> 58 years), which was consistent with prior studies to some extent. Still, there was no significant difference in the middle-aged (≥ 45 and ≤ 58 years) group. Therefore, sociodemographic disparities exist in the prevalence of VI, and more targeted efforts are required for preventing and treating low vision and blindness in high-risk groups.
The mechanism of sleep duration has not been fully explained. Short sleep duration may be attributed to difficulty falling asleep, sleep fragmentation, and early awakenings. Long sleep duration may be due to poor circadian entrainment, compensation for fragmented sleep, and lower sleep efficiency [10, 26]. Sleep deterioration and related VI may result from several diseases [27]. In turn, VI may further increase mood disturbance and even worse sleep disorders. Further, respondents with VI tend to exhibit a shortened photoperiod and reduced circadian entrainment [8]. The decline or loss of light perception leads to circadian misalignment, further contributing to abnormal sleep duration. Therefore, ophthalmologists must recognize the possibility of sleep disturbance in subjects with VI and participate in effective management accordingly.
In particular, long sleep duration had more significant potential for VI than short sleep duration in multilevel logistic regression models. The result was similar in subset analyses of middle-aged respondents. However, this association was not significant in subset analyses of elderly respondents. It suggests that those who sleep for a long duration may require greater amounts of sleep, reflecting worse sleep conditions, and have a greater risk of VI, especially in the middle-aged group. Additional studies examining the causal relationship between sleep durations and VI are needed.
To our knowledge, this study is the first large-scale population-based study to explore the associations between self-reported sleep duration and VI among Chinese. Self-reported sleep duration and the prevalence of VI are known to reflect ethnic differences [28, 29]. Therefore, it is essential to investigate the association between VI and sleep duration among older adults in China. Such research would be more convincing if adjusted for sociodemographic characteristics, health behavior, and medical history. All may affect the relationship between self-reported sleep duration and VI.
However, this study is not without limitations.
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Due to the cross-sectional nature of the study, causality could not be established.
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Sleep duration and visual function were subjectively assessed through self-reported questionnaires. Details outlining the severity of VI through visual acuity were not recorded. Moreover, an objective assessment of sleep quality using polysomnography or actigraphy was not conducted. However, according to previous studies [30], self-reported sleep duration is sufficiently consistent with objective methods such as actigraphy. In large-scale studies, the evaluation of sleep duration through self-reported questionnaires is a fast, simple, and widely accepted method [31].
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The correlation between the severity of VI and the severity of sleep difficulties was not explained.
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Though the study was adjusted for sociodemographic characteristics, health behavior, and medical history, it was not adjusted for mood, medication, and exposure to artificial light at night, affecting sleep duration [32, 33].