It is well known that sleeping poorly can affect judgment, mood, and ability to learn and hold on to information. New research indicates there's a good reason they call it shut eye— not sleeping well could also lead to blindness.
Insomnia, snoring, daytime sleepiness and even sleeping too much could all increase the risk of glaucoma, a common eye condition that impacts millions of people and can lead to vision loss, according to a decade-long study published Wednesday in the peer-reviewed journal BMJ Open.
The research examined data from more than 400,000 people between the age of 40-69 who participated in a UK Biobank study, the world’s first large prospective cohort study to look comprehensively at sleep patterns leading to glaucoma, which is the leading cause of blindness and estimated to affect 112 million people worldwide by 2040. The disease is characterized by progressive loss of light sensitive cells in the eye and optic nerve damage.
To explore the connection between sleep and glaucoma, the researchers analyzed risk among people with various sleep behaviors: insomnia; too much or too little sleep; night or morning chronotypes (‘owls’ or ‘larks’); daytime sleepiness; and snoring.
"Normal" sleep duration was defined as seven to nine hours per night. Anything outside this range was characterized as too little or too much. Chronotype was defined according to whether the person described themselves as more of a morning lark or night owl.
Insomnia severity—trouble falling asleep at night or frequent waking—was classified as never/sometimes or usually, whereas subjective daytime sleepiness was defined as never/rarely, sometimes, or frequent.
Participants also answered questions about their age, sex, race/ethnicity, educational attainment, lifestyle, and weight (BMI).
Medical records and death registration data were used 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 (March 2021), whichever came first.
During an average monitoring period of just over 10.5 years, 8690 cases of glaucoma were identified.
Those with glaucoma tended to be older and more likely to be male and to have higher blood pressure, diabetes or smoking history than those who weren’t diagnosed with the disease.
With the exception of chronotype, the other four sleep patterns and lifestyles were all associated with varying degrees of heightened glaucoma risk.
Short or long sleep duration was associated with an 8% heightened risk; insomnia 12%; snoring 4%; and frequent daytime sleepiness (20%).
In contrast to those with a healthy sleep pattern, snorers and those who experienced daytime sleepiness were 10% more likely to have glaucoma, while insomniacs and those with a short/long sleep duration pattern were 13% more likely to have it.
What are the possible connections between sleep and glaucoma?
One explanation suggested by scientists is the internal pressure of the eye, a key factor in the development of glaucoma, rises when a person is lying down and when sleep hormones are out of kilter.
Another is that repetitive or prolonged episodes of low levels of cellular oxygen, caused by sleep apnoea (sudden stopping of breathing during sleep), might cause direct damage to the optic nerve.
Furthermore, depression and anxiety, which often are connected with insomnia, may also increase the internal eye pressure, possibly because of dysregulated cortisol production, the team said.
Researchers noted that the study is observational and therefore cannot establish cause. It is possible glaucoma might itself influence sleep patterns, rather than the other way round. Plus, it's important to note the study relied on self-reports. Still, the findings are notable and could encourage people to seek help for sleep issues, researchers say.
The research team said: “As sleep behaviors are modifiable, these findings underscore the necessity of sleep intervention for individuals at high risk of glaucoma and potential ophthalmologic screening among individuals with chronic sleep problems to help prevent glaucoma."