Association Between Vision-Related Functional Burden and Sleep Disorders in Adults Aged 20 and Over in the United States

Abstract

Purpose: The impact of functional vision, rather than visual acuity, on sleep disorders is not well understood. This study estimated the relationship between vision-related functional burden and sleep disorders among a nationally representative sample in the United States.

Methods: Data from the National Health and Nutrition Examination Survey (NHANES) 2005–2008 were analyzed, which included a total of 10,914 US adults 20 years and older. Sleep disorders and vision-related functional burden were measured by the NHANES questionnaire sleep disorders section and vision section, respectively. Logistic regression was used to explore the association between vision-related functional burden and sleep disorders.

Results: A total of 9384 NHANES participants had complete functional vision and sleep disorders data. The mean age at baseline was 47.8 years, and the weighted prevalence of sleep disorders among adults with vision-related functional burden was 20.3%. After controlling for age, gender, race, smoking status, drinking frequency, general health condition, hypertension, diabetes, coronary heart disease, and depression, vision-related functional burden remained significantly associated with sleep disorders (adjusted odds ratio, 1.502; 95% confidence interval, 1.210–1.864; P < 0.001), whereas the association between presenting visual acuity and sleep disorders was not statistically significant.

Conclusions: Vision-related functional burden rather than impairment of visual acuity was related to the increased prevalence of sleep disorders in adults 20 years and older in the United States.

Translational Relevance: Our study provides insight into the relationship between functional vision and sleep disorders. It should be noted that individuals who report vision-related functional burden might be at risk of sleep disorders.

Introduction

More than 300 million people worldwide have vision loss.¹ Cataract, glaucoma, ametropia, macular degeneration, diabetic retinopathy, and optic neuropathy are the most common causes of vision loss.^2–4 Individuals with low vision perceived a marked impairment in their functional status and quality of life, including sleeping, moods, and daily activities.^5,6 

Around a third of one's life span is spent sleeping, demonstrating the importance of sleep to human beings. In the United States, it has been reported that one-third of adults are not getting enough sleep and rest every day, and 50 to 70 million have chronic sleep disorders.^7,8 In recent decades, sleep disorders have been shown to be associated with normal physiologic, psychological, social, and emotional functions during daily life.⁹ The most common sleep disorders include sleep apnea, insomnia, restless leg syndrome, narcolepsy, and abnormal circadian rhythms, among others. These disorders have been related to an increased risk of cardiovascular and cerebrovascular diseases, obesity, diabetes, metabolic disorders, and other diseases.^10–12 It is noteworthy that more and more studies have indicated a correlation between sleep and vision. The elderly with impaired vision in Japan and South Africa presented more sleep difficulties than those without visual impairment, including short sleep duration, poor sleep quality, and irregular sleep–wake patterns.^13,14 Another study found that photic input maintains the circadian rhythm through the suprachiasmatic nucleus (SCN) of the hypothalamus, and photic input decrease could negatively affect sleep.¹⁵ For blind people, desynchronized rhythms may lead to sleep disturbances and depression.¹⁶ 

Although many studies have found a link between sleep and vision, there is still a lack of research on the impact of functional vision on sleep disorders. Visual function usually refers to the performance of visual system components; however, in this study, functional vision is defined as visual task–related ability in daily life under real-world scenarios based on data from the National Health and Nutrition Examination Survey (NHANES) 2005–2008. If a person indicated difficulty with any specific vision-related daily life tasks on the NHANES questionnaire, they are considered to have impaired functional vision or a visual burden. The aim of this study is to investigate the impact of impaired functional vision rather than visual acuity on daily life and the potential relationship between vision-related burden and sleep disorders diagnosed by a doctor in adults 20 years and older in the United States. 

Methods

Study Population

The NHANES provides data on the health statistics of Americans. In this study, we used public data from two consecutive NHANES cycles (2005–2006 and 2007–2008). A total of 10,914 persons 20 years and older underwent a series of standardized interviews and examinations, which included demographic data, physical examination information, and socioeconomic and health-related issues. Participants who had complete data on vision-related functional burden and sleep disorders were finally included (Fig.). Given that the NHANES adopts a stratified multistage sampling design, weighted data were required for analysis. The project was approved by the Human Subjects Committee and obtained the written informed consent of all participants. All procedures adhere to the principles in the Declaration of Helsinki. 

Figure.

 

Schematic overview for enrolling study participants.

Evaluation of Sleep Disorders

The primary outcome variable was participants who had sleep disorders as diagnosed by a doctor. Sleep disorders data were acquired from the sleep disorders section (abbreviated “SLQ”), which provided personal interview data on several sleep disorders topics in the NHANES questionnaire data. The same SLQ was used in NHANES from 2005 to 2008. During the interview, participants were asked, “Have you ever been told by a doctor or other health professional that you have a sleep disorder?” The answers were yes, no, refused, and don't know. The sleep disorders included sleep apnea, insomnia, restless legs, and others. 

Evaluation of Functional Vision

The main exposure variable for this study was whether there were any functional difficulties from the vision section (abbreviated “VIQ”), which provided personal interview data on several vision topics in the NHANES questionnaire data. Six questions were asked to evaluate the degree of visual functional difficulties, including (1) reading ordinary newsprint, (2) doing close work or chores, (3) seeing steps or curbs in dim light, (4) noticing objects to the side, (5) finding an object on a crowded shelf, and (6) driving in the daytime in a familiar place. Each question was graded on a 5-point scale: none, little, moderate, extreme, and unable to do due to eyesight. Participants were considered to have difficulty with a particular task if they reported moderate to extreme difficulty or were unable to complete the activity due to vision problems.¹⁷ Participants with vision-related functional burden were defined as those who reported moderate or worse in any of the six questions. 

Covariates

Potential confounders included demographic data: age, gender (male or female), and race (Mexican, other Hispanic, non-Hispanic white, non-Hispanic black, and other race, including multiracial); general health condition; health-related behaviors (smoking status, drinking frequency); systemic disease diseases (diabetes, hypertension, and coronary heart disease); presenting visual acuity; depression; and sleep duration. Information about age, gender, and race was derived from the NHANES demographic data module. The NHANES questionnaire data module provided information on the remaining variables. General health condition: “Would you say your health, in general, is excellent/very good/good/fair/poor/refused/don't know?” Smoking status: “Do you now smoke cigarettes?” Drinking frequency: “How many days do you drink alcohol per week, month, or year?” Hypertension: “Have you ever been told by a health professional that you had hypertension?” Diabetes: “Have you ever been told by a health professional that you have diabetes or sugar diabetes?” Coronary heart disease: “Has a doctor or other health professional ever told you that you had coronary heart disease?” Depression: “Over the last 2 weeks, how often have you been bothered by the following problems: feeling down, depressed, or hopeless?” Sleep duration: “How much sleep do you usually get at night on weekdays or workdays?” Presenting visual acuity for each eye was measured upon usual correction including eyeglasses, contacts, eyeglasses and contacts, or no correction. 

Statistical Analysis

This study performed data analysis using the statistical software packages R version R-4.2.2 (R Foundation for Statistical Computing, Vienna, Austria) and SPSS software, version 25.0 (SPSS, Inc., Chicago, IL, USA). During data processing, first of all, we combined two consecutive NHANES cycles (2005–2006 and 2007–2008) by using the packages “haven,” “readr,” and “dplyr.” Due to missing data in the covariates, we used the package “mice” to perform multiple imputations, including five data sets after interpolation. The sample weights were then calculated as 1/2*wtmec2yr, because 4-year weights should be calculated as half of 2-year weights according to the NHANES Analytic and Reporting Guidelines. Finally, we obtained the final data after weighting the data with the package “survey.” For further analysis, we compared the distribution of baseline characteristics of the study participants, including age, gender, race, general health condition, health-related behaviors, systemic diseases, presenting visual acuity, depression, sleep duration, and sleep disorders using SPSS software. For continuous variables, mean and standard deviation (SD) were used, and for categorical variables, numbers and weighted percentages were used. Then, the t-test and the χ² test were performed for age comparisons and categorical data comparisons. Survey-weighted logistic regression models were used to assess the relationship between vision-related functional burden and risk of sleep disorders. Odds ratio (OR) and 95% confidence intervals (CIs) were calculated. A two-sided P < 0.05 was considered statistically significant. 

Results

Participants’ Characteristics

This analysis included a total of 9384 persons whose mean (standard error [SE]) age was 47.8 (17.8) years, and 673 (7.3%) of these participants had sleep disorders (age, 51.9 [15.7] years; 371 [55.0%] male and 302 [45.0%] female). Of the individuals with sleep disorders, 52.0% slept less than 7 hours per day, and 4.5% felt depressed nearly every day. Overall, 44.0% of respondents were current smokers, 5.7% had a poor general health condition, and many had systemic diseases such as hypertension (46.9%), diabetes (17.2%), and coronary heart disease (7.3%) (Table 1). 

Table 1.

 

Sociodemographic and Clinical Characteristics of Participants by Sleep Disorders Status

 

Association Between Vision-Related Functional Burden and Sleep Disorders

Among US adults 20 years and older with sleep disorders, the weighted prevalence of vision-related functional burden was 20.3%. The weighted prevalence of vision-related difficulty was 10.9% for reading ordinary newsprint, 9.0% for close work or chores, 11.3% for seeing steps or curbs in dim light, 4.8% for noticing objects to the side, 6.7% for finding an object on a crowded shelf, and 2.6% for driving in the daytime in a familiar place. In addition, approximately 36.1% of individuals with sleep disorders had presenting visual acuity of less than 20/30. The vision-related difficulty was more common in those who had sleep disorders (P < 0.001), but there was no significant difference between those with and without sleep disorders in terms of presenting visual acuity (P = 0.519) (Table 2). In contrast, the weighted prevalence of sleep disorders was 14.1% among those with vision-related functional burden and 6.5% among persons without vision-related functional burden. There was a significant difference in sleep disorders between persons with and without vision-related functional burden (P < 0.001) (Table 3). 

Table 2.

 

Functional Vision Characteristics of Participants by Sleep Disorders Status

 

Table 3.

 

Characteristics of Participants by Vision-Related Functional Burden Status

 

Factors Associated With Vision-Related Functional Burden and Sleep Disorders

Table 4 shows the ORs and 95% CIs for the presence of sleep disorders determined by vision-related functional burden. In model 1, the OR of vision-related functional burden was significantly higher in those with sleep disorders than in those without sleep disorders, according to multivariate logistic regression analysis after adjusting for age, gender, and race (OR, 2.241; 95% CI, 1.835–2.738; P < 0.001). After further adjustment for smoking status, drinking frequency, general health condition, hypertension, diabetes, and coronary heart disease in model 2, the OR was 1.635 (1.322–2.021, P < 0.001); in model 3, the OR was 1.502 (1.210–1.864, P < 0.001) after adjusting for age, gender, race, smoking status, drinking frequency, general health condition, hypertension, diabetes, coronary heart disease, depression, and sleep duration. However, there was no statistically significant difference between sleep disorders and presenting visual acuity in any models after controlling for potential confounders (model 1, model 2, and model 3). 

Table 4.

 

Multivariate Logistic Regression Model of the Relationship Between Vision-Related Functional Burden and Sleep Disorders

 

Discussion

This study focused on the association between self-reported vision-related functional burden and sleep disorders in a representative sample of adults in the United States. We found that participants who reported vision-related functional burden were more likely to have sleep disorders. This result is consistent with previous studies. Reportedly, a U-shaped relationship was observed between visual impairment and sleep duration. In Korean adults, both short (≤5 h/night) and long (≥9 h/night) sleep durations were significantly related to increased visual impairment.¹⁸ Among elderly persons with visual impairments, an epidemiologic study indicated that poor sleep, frequent awakenings, and difficulty falling asleep after awakening at night are more common.¹⁹ Tamura et al.¹³ stated that blind individuals had more difficulty with irregular sleep–wake patterns or waking up at the desired time. In the present study, we observed an OR (95% CI) for vision-related functional burden among individuals with sleep disorders of 1.502 (1.210–1.864) after adjusting for demographic factors, health-related behaviors, systemic diseases, and depressed moods. Those who reported difficulty seeing steps or curbs in dim light or finding objects on a crowded shelf were more likely to have sleep disorders. Our findings indicated that vision-related functional burden may be a predictor of sleep disorders. Although the causality remains unclear, there are several possible reasons for this. 

One possible reason may be related to depression. In recent years, mental and psychological factors have been shown to be closely related to sleep disorders, particularly depression.²⁰ In our study, there was a significant difference in depression between people with and without sleep disorders. The interaction of sleep disorders, visual impairment, and depression should also be noticed. Impairment or loss of vision leads to an inability to independently engage in necessary basic activities and perform desired activities of daily living. Continuing this pattern for a long period of time may result in significant changes in self-esteem, self-efficacy, and mental and psychological well-being, which may contribute to the development of depression and adversely affect sleeping such as sleep quality and sleep duration.²¹ In addition, limited outdoor activities lead to fewer exposures to natural sunlight. Sunlight can increase dopamine secretion, which induces positive changes in mood.^22,23 Dopamine pathways in the SCN are also involved in the regulation of wake and sleep.²³ 

On the other hand, those who self-reported vision-related functional burden tend to be exposed to more artificial indoor light, such as short-wavelength light, due to a lack of outdoor activities. Short-wavelength light selectively stimulates the intrinsically photosensitive retinal ganglion cells (ipRGCs), which are another type of photoreceptor cell but differ from cone and rod cells.^24–26 ipRGCs do not rely on form vision; however, they have photosensitive ability and can be influenced by natural light, day and night, as well as artificial light.²⁷ It also has a role in regulating circadian rhythm, melatonin secretion, sleep, and mood.²⁸ 

Furthermore, for completely blind participants, who account for a small proportion of the total, vision-related functional burden may affect sleeping by interfering with the circadian rhythm. Reportedly, individuals with no or limited light perception were more likely to experience sleep disorders than those with some degree of light perception.²⁹ The circadian rhythm system controls sleep by altering efferent signals from the SCN of the hypothalamus to regulate sleep–wake states, promoting night sleep and daytime wakefulness.³⁰ Light stimuli are required for circadian rhythms and are considered the key synchronizer of sleep–wake cycles.³¹ Alterations of light–dark exposure caused by blindness have been shown to impair the ability of the SCN to adjust the circadian cycle, resulting in sleep–wake cycle synchronization problems.³¹ 

As of yet, no causal relationship between functional vision and sleep disorders has been definitively established. The preceding studies indicated that visual impairment has a negative impact on sleep, while some studies found that sleep disorders may play a role in the occurrence of certain eye diseases that impair visual function. Sleep apnea is the most common sleep-disordered breathing condition.³² Some studies have found a link between obstructive sleep apnea (OSA) and glaucoma, with patients with OSA having a higher prevalence of glaucoma and higher intraocular pressure values than patients without OSA.^33,34 In addition, OSA has been associated with nonarteritic anterior ischemic optic neuropathy, which is the most common cause of acute unilateral vision loss related to the optic nerve.³⁵ Yang et al. reported a hazard ratio of 3.8 in patients with newly diagnosed OSA compared to the non-OSA group.³⁶ 

However, there are several limitations to this study. First, the data used are old, since the NHANES only collected functional vision data from 2005 to 2008. We look forward to the release of an updated version of the NHANES questionnaire on functional vision. Second, despite the fact that participants with vision-related functional burden had a higher prevalence of sleep disorders than control subjects, there did not appear to be a statistical difference in visual acuity between those with and without sleep disorders. One possible reason for this difference is that the accuracy of self-reporting to evaluate the degree and nature of visual impairment is questionable. Besides, the detection of functional vision may also require more objective and extensive testing. Another limitation is that we were unable to assess the relationship between vision-related functional burden and specific sleep disorders such as insomnia, apnea, and restless legs due to excessive data loss in the questionnaire. Furthermore, there is a lack of more objective assessments of sleep quality in the questionnaire, because some measures, such as somnography and actigraphy, are not feasible in this large cohort. In light of this, additional longitudinal cohort studies are required to determine causal relationships. 

Conclusions

In conclusion, the present study showed that vision-related functional burden in adults 20 years and older in the United States was related to the increased prevalence of sleep disorders. We found strong associations between sleep disorders and impaired functional vision rather than visual acuity. Although the causal relationship remains unclear, the possibility of sleep disorders among patients with vision-related functional burden should also be considered. 

Acknowledgments

Disclosure: R. Xue, None; G. Wan, None