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This Is What It's Like to Have No Internal Clock

Completely blind people lack light perception, which can mess with their lives in more ways than just abnormal sleep patterns.

Hannah Flynn

Jovo Jovanovic / Stocksy

Try this experiment: Sit down in a quiet place with no distractions, and without looking at a clock or a watch see if you can accurately guess when a minute has passed. You were pretty close right? Now try it blindfolded. You’ll likely find this much harder to do accurately. Now, imagine what it must be like to live like that, and how it’d affect your sense of time.

People who are blind can be affected by something known as non-24-hour sleep-wake disorder, a condition that means their body’s clock is not tuned into the 24-hour day. This happens in people who have no light perception—either the light sensitive cells in their eyes have been destroyed, or the optic nerve damaged—which means light signals don’t reach the brain. This leads to a disorder of the person’s circadian rhythm (the physical, mental, and behavioral changes that follow a daily cycle), and it can make their lives pretty messy.

Though there are actually very few completely blind people with no light perception, the way their brains work in the absence of light has provided some fascinating insight into how our brains and bodies are affected by the circadian cycle. Circadian disturbances were first noted in blind people in the 1940s. The earliest research on the subject noted that some blind people had ‘inverted rhythms’ in their heart rate, blood pressure, temperature and urine output—this means that their bodies were functioning in the opposite way of people who can perceive light. Normally, all these would be expected to drop regularly at night when asleep, when many of our metabolic processes slow down. Yet, in these patients they didn’t.

Researchers also noted that many of them had disrupted sleep cycles, and we now know this is because melatonin isn’t produced when no light is detected by the retina. A sighted person will feel awake when they are exposed to sunlight, but sleepy when it gets dark. People with these disorders simply don’t get these cues.

Mark Threadgold is a blind ex-serviceman whose career in the army ended eighteen years ago when a head injury caused his optic nerves to be severed. He is now completely blind and has non-24-hour sleep-wake disorder. “What I have found in the past is that over the space of about a fortnight, my sleep pattern would basically invert,” he says. “I would sleep all day and be up all night, and over the next fortnight it would wind itself back, and get back on track—but it was an absolute pain,” he says.

His experience is typical of about four or five percent of people who have the disorder and have a cycle that is slightly longer or shorter than the normal 24-hour day, says Steven Lockley, an associate professor of medicine at Harvard Medical School. Lockley add that othher people with the disorder may have no perceptible rhythm to their sleep pattern, and a further 10 percent of people with the disorder may have no clear circadian rhythm, but not experience any sleep problems.


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All of these presentations can have extremely disruptive effects on people’s lives. Being unable to get up in the morning can impact a person’s ability to go to work, or school or engage socially with other people. “You just don’t want to go out if you’re sleeping at the wrong time of day,” Threadgold says. “So fine, you can get up in the morning and do your thing, but if you fall asleep at 11 am and then you get up at four or five in the afternoon what do you do?”

This inability to synchronize with the 24-hour world has a real impact on people’s abilities to keep a job or have a social life, Lockley says. "Some patients have even said it is worse than being blind, which is a pretty stark statement."

Threadgold says he’s managed to get on top of his sleep problems in the past three years by “living by the clock,” and committing to a routine of getting up and eating at the same time every day and paying close attention to his nutrition and exercise routine. Being aware of helps assert even a little control. However, there are some people with the condition who don’t even realize they have it. Some of these people just label themselves ‘insomniacs.’ In fact, it is very often other people around them who notice it, says Renata Gomes, head of research at Blind Veterans UK, who have recently launched study on the condition with the University of Oxford.

“I still have blind veterans who are awake from 4 am if their clocks aren’t working very well, or they forget and they turn up at work at half five or six am when everything is still shut,” Gomes says. “Their neighbors and their family complain that they are building their sheds or doing their gardening so early in the morning. They don’t have any notion of time, as time is associated with the circadian cycle.”

Other factors such as mental health problems, dementia, and diabetes can also disturb sleep, and people with non-24 sleep-wake disorder may not see the specialists who realize the underlying problem, and blame those factors instead.

Lockley was one of the first people to study the impact of the drug tasimelteon (that targets the same receptors as melatonin) in blind people with the disorder, and thinks his findings could be used to develop ways to help people with other circadian disorders, such as delayed sleep phase disorder, jet lag and even shift workers.

“Tasimelteon is the first drug that was approved to regulate the circadian clock, other drugs that were tried for other circadian disorders didn’t affect the clock—they affected the symptoms and the sleepiness,” he says. Though this is the only drug currently available for people with circadian rhythm disorders, more could be developed as we learn how to control the brain “on a molecular level,” he adds.

For Lockley and other researchers—including those who won the 2017 Nobel Prize in Physiology or Medicine for their work on circadian rhythms—there’s a renewed focus on how blind people with non-24 sleep-wake disorder can live more fulfilling lives, as well as a deeper understand of how our circadian rhythms can be manipulated.

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