About blindness and partial sight
Non-24 is a circadian rhythm disorder. Your circadian rhythms are controlled by your master body clock and tell you when to sleep, when to wake, when to eat, among other things.
In most people, the master body clock runs slightly longer than 24 hours. What this means is that rather than cycle on a 24-hour day, most people's natural rhythms actually cycle a bit longer. Whether the cycle runs two minutes or 30 minutes longer, if you have Non-24 these minutes add up day after day, a few one day adding to a few more the next, eventually causing a noticeable change in the times during the day when your body expects to sleep and expects to be awake.
Though Non-24 may appear to be a sleep disorder, it isn't. It's actually a serious, chronic circadian rhythm disorder very common in people who are totally blind, and it can arise at any age. Currently, there are 1.3 million people who are legally blind in the United States. Of the legally blind, 130,000 have no light perception (i.e., totally blind), and as many as 70% suffer from Non-24.
Non-24 brings about two significant symptoms.
First is a profound inability to sleep or to stay asleep at night, and the second is an overwhelming urge to sleep during the day. Both of these changes occur because the internal body clock is out of sync with the 24-hour day-night cycle, which is due to the internal master clock continuously shifting in and out of alignment with the 24-hour day-night cycle. And when poor sleep happens, sleep deprivation may make it difficult to focus on the task at hand.
Non-24 comes about when the master body clock runs on its own natural rhythm. Hence the name, Non-24, which indicates a master body clock that is not 24 hours long. For unknown reasons, most people's body clock runs a little longer than 24 hours, which means most people could have Non-24 to some degree. The difference is that for sighted people, environmental light cues signal the brain to reset the master body clock every day to 24 hours.
For people who are totally blind, the master body clock runs its natural course. This means that if your body clock runs on a 24.5-hour schedule, today you're 30 minutes behind and tomorrow your body clock will be an hour behind. The next day will be 90 minutes, and so on. Day by day, this time adds up until you're many hours behind, creating a rhythm that's out of sync with the typical day-night cycle. Eventually, your body operates as if night is day and day is night. While you could try to maintain your usual schedule, more often than not you have a hard time sleeping at night and then feel an overwhelming urge to sleep during the day. In time, you once again reach the point when your body clock is in sync with the typical day-night cycle. But then, just as quickly, it moves out of sync again.
The body clock is your natural timing mechanism, and for most people, sighted or blind, it runs a little longer than 24 hours. Thus, it's a non-24-hour clock. For some, it runs just a few minutes longer, and for others it runs much longer. The reason for this is not known.
For example, if your body clock is 24.5 hours, today you're running a half hour behind. Tomorrow you're an hour behind, and so on, until your natural rhythms have you sleeping during the day and awake at night. This continues and eventually your sleep-wake cycle briefly syncs up with the typical day-night cycle. Then it begins to move out of sync again. Some people experience a full circadian cycle as short as one and a half months. For others, it can be several months before their sleep-wake cycle is realigned with the 24-hour day.
The eye has two functions: to allow us to see images and to take in light. This light then signals the time of day to the brain. In people who are sighted, the non-24-hour master body clock is reset every day to 24 hours in the same way that hands on a clock can be reset. This ensures that the circadian rhythms synchronize to the typical day-night cycle.
For people who are totally blind, there are no such light cues. The body clock is left to run its natural course, with extra minutes adding up day by day until your circadian rhythms are essentially upside down from a typical 24-hour day.
Circadian rhythms are your body's tide. They control its natural ebb and flow. They keep its daily activity in sync with the 24-hour day, as well as the timing of sleep and wakefulness. If the circadian rhythms are out of sync, these hormones can be released at the wrong times of day, creating difficulties sleeping at night, and the urge to sleep during the day.
This is how having circadian rhythms that are out of sync with the 24-hour day can impact the natural ebb and flow of the body.
Because its effects are so wide-ranging, Non-24 may hinder the methods you use to get through the day. It may sap your energy. You may suddenly fall asleep at inopportune times, and it may make crucial daily tasks a challenge, such as counting bus stops so you know when to get off.
Living with Non-24 may make you feel as though no one understands what you're going through, and this sense of being alone only makes the effects feel that much worse. The truth is, you're not alone. There are many other people living with Non-24 who are experiencing many of the same challenges you do.
Non-24 is not a sleep disorder. It is a serious, chronic circadian rhythm disorder that can greatly impact your life.
If you have some of the symptoms, whether to a mild or intense degree, you may have Non-24.
A few of the key symptoms are: