Prior studies indicate visual impairment negatively impacts sleep while others found sleep disorders to play a role in occurrence of certain eye diseases that impair visual function, for example, sleep apnea and glaucoma.  Photo: Bruce Mars/Unsplash.

It has been well-documented that individuals with low vision perceive marked impairment in quality of life categories concerning mood and daily activities. Indeed, many studies have found links between sleep and vision, but research is scarce when specifically looking at the impact of functional vision on sleep disorders. In one recent study, researchers looked at the impact of vision-related functional burden, rather than visual acuity, on sleep disorders.

The sample used from the National Health and Nutrition Examination Survey (NHANES) from 2005 to 2008 was nationally representative of the US and included 9,384 participants aged 20 years or older; all subjects had complete functional vision and sleep disorder data. Sleep disorders and vision-related functional burden were both measured by the NHANES questionnaire sleep disorder and vision sections.

It should be noted that the study authors defined functional vision differently than typical use, as follows: visual task-related ability in daily life under real-world scenarios based on data from the NHANES. This contrasts with the more widely used definition of the performance of visual system components.

Of all participants, mean age was 47.8 years and weighted sleep disorder prevalence among those with vision-related functional burden was 20.3%; this burden remained significantly associated with sleep disorders even after adjustment for factors of age, sex, race, smoking status, drinking frequency, general health condition, hypertension, diabetes, coronary heart disease and depression. To demonstrate functional burden, those reporting difficulty seeing steps or curbs in dim light or finding objects on a crowded shelf were more likely to experience sleep disorders.

The relationship between vision-related functional burden and sleep disorder prevalence echoes that of previous studies. One found a U-shaped relationship between visual impairment and sleep duration while another saw short (≤5h/night) and long (≥9h/night) sleep durations in Korean adults to relate to increased visual impairment. Among elderly with visual impairments, poor sleep, frequent awakenings and difficulty falling asleep were more common. Those who are blind were found in on study to have more difficulty with irregular sleep-wake patterns or waking up at the desired time.

There are a few reasons this relationship may exist. One possibility is related to depression, as mental and psychological factors have closely been related to sleep disorders and depression in particular. Loss of vision can lead to challenges engaging in basic activities independently, and if this is continued over a longer duration, this may result in self-esteem, self-efficacy and mental and psychological well-being changes that contribute to depression development, thus hindering proper sleep. As well, less time outdoors would result in lesser effects seen with natural sunlight to increase dopamine secretion, inducing positive mood changes. What’s more, dopaminergic pathways in the suprachiasmatic nucleus of the hypothalamus are involved in regulating sleep and wake. In this study, there was a significant difference in depression between those with vs. without sleep disorders, furthering this already documented correlation.

Completely blind participants made up a small proportion of the total included in this study. They may have their sleeping be affected by vision-related functional burden through interference with natural circadian rhythm. One study surveyed that those with little to no light perception more likely experienced sleep disorders than those with some degree of light perception. The suprachiasmatic nucleus has been shown to adjust the circadian cycle due to alterations of light-dark exposure caused by blindness, resulting in sleep-wake cycle synchronization issues.

For clinical application, the authors convey that, “although the causal relationship remains unclear, the possibility of sleep disorders among patients with vision-related functional burden should also be considered.”