Poor quality sleep including too much or too little shut-eye, daytime sleepiness and snoring, could be linked to a heightened risk of developing irreversible sight loss, suggests a new large UK Biobank study.
The findings indicate the need for sleep therapy in those at high risk of glaucoma and the importance of regular eye checks for those with chronic sleep disorders to look for early signs of the disease.
Glaucoma – a common eye condition where the optic nerve, which connects the eye to the brain, becomes damaged – is a leading cause of blindness and will likely affect roughly 112 million people worldwide by 2040.
While the condition's causes and contributory factors are still poorly understood, if left untreated, glaucoma can progress to irreversible blindness.
And though screening the whole population may not be cost-effective, targeted checks for high-risk groups might be, suggest the researchers, along with knowledge from previous studies that suggest sleep disorders could be an important risk factor.
But to understand this further, they wanted to find out more about the risk of glaucoma among people with different sleep behaviours including insomnia; sleeping too much or too little; night or morning 'chronotypes' (your body's natural tendency to want to sleep at a certain time) daytime sleepiness, and snoring.
"Our research was motivated by a colleague, who got the feeling that his sleep problems were always followed by the worsening symptoms of glaucoma (diagnosed several years ago). Hence, we come up with the question of whether glaucoma is associated with some specific sleep behaviours," explains Professor of Epidemiology Huan Song of West China Biomedical Big Data Center.
The new results published in the open access journal BMJ Open draw on 409,053 participants in the UK Biobank, all aged between 40 and 69 in 2006-10 when they were recruited, and who had provided details of their sleep behaviours.
Sleep duration was defined as 'normal' (if seven to less than nine hours a day) and as too little or too much, outside either end of this range. 'Chronotype' was defined according to whether the person described themselves more of a 'morning lark' or a 'night owl'.
Insomnia severity – when you regularly have problems sleeping, including drifting off or waking up in the night – was classified as never/sometimes or usually. Meanwhile, subjective daytime sleepiness was categorised as never/rarely, sometimes or frequent.
Background information on potentially influential factors were also gathered from the questionnaires filled out at time of recruitment, including age (average being 57), sex, race/ethnicity, educational attainment, lifestyle, weight (BMI), and residential area level of deprivation.
Researchers used medical records and death registration data to track the health and survival of all the participants until a first diagnosis of glaucoma (hospital admission), death, emigration, or the end of the monitoring period (31 March 2021), depending on which came first.
During an average assessment period of just over 10.5 years, 8,690 cases of glaucoma were identified.
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Those with the disease tended to be older and more likely to be male, an 'ever time' smoker (always been one), and to have high blood pressure or diabetes than those who weren't diagnosed.
With the exception of chronotype, the other four sleep patterns/behaviours were all associated with varying degrees of heightened glaucoma risk.
Specifically, a short or long sleep duration was associated with an 8% increased risk, insomnia 12%, snoring 4% and frequent daytime sleepiness 20%.
Plus, compared to participants with a healthy sleep pattern, snorers and those who experienced daytime sleepiness were 10% more likely to have glaucoma, while insomniacs and people with a short/long sleep duration pattern were 13% more likely to have glaucoma.
The results were also similar when categorised by different types of the disease.
"After the literature review, indeed, we found that several studies have shown a high prevalence of sleep disorders among patients with glaucoma," explains Song. "Also, the fact that peak intraocular pressure [fluid pressure of the eye] occurs during the nocturnal period, probably due to the head and body position during sleep, suggests that sleeping patterns might contribute to the development or progression of glaucoma.
"In addition, another concern about sleep-related research is most of them focus on a single sleep behaviour (e.g. insomnia), whereas sleep adversities tended to co-occur within an individual.
"Therefore, taking advantage of enriched and high-quality data from UK Biobank, we dig into the research question by elucidating the major sleep patterns identified based on individual sleep behaviours, as well as their association with subsequent glaucoma among UK Biobank participants."
As a result, Song emphasises that their research demonstrates that certain sleep adversities, including snoring, daytime sleepiness, insomnia, and short/long duration, might have either individually or jointly contributed to a subsequent risk of glaucoma.
As this is an observational study, it can't establish specific causes. It relied on participants self-reporting rather than objective measurement and reflected one point in time only, the researchers admit. Glaucoma itself might even influence sleep patterns, rather than the other way around, they add.
However, there are potentially plausible biological explanations for the links uncovered between sleep disturbance and glaucoma.
For example, the internal pressure of the eye (as Song mentions above), a key factor in the development of glaucoma, rises when a person is lying down and when sleep hormones are out of kilter, which occurs in insomnia, the researchers explain.
Depression and anxiety, which are often experienced alongside insomnia, may also increase the internal eye pressure, possibly because of dysregulated cortisol (a stress-related hormone) production.
And similar, repetitive or prolonged episodes of low levels of cellular oxygen, caused by sleep apnoea – when your breathing stops and starts while you sleep – might cause direct damage to the optic nerve, it has been suggested.
"These findings underscore the necessity of sleep intervention (e.g. physiotherapy and drug therapy) among individuals with a high risk of glaucoma as well as potential ophthalmologic screening among individuals with chronic sleep problems for glaucoma prevention," concludes Song.
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