Non-24 is a disorder most common in people who are blind. Several studies suggest that most people who are totally blind may have Non-24 and the sleep disruptions that go with it due to a lack of light perception. 70% of people who are blind suffer from the effects of Non-24.

The eye has two functions. One is to see, and the other is to take in light, which signals the time of day to the brain. Lack of light perception is a key factor in the onset of Non-24, which can happen at any age, regardless of the cause of blindness. Non-24-Hour Sleep-Wake Disorder (Non-24) is a circadian rhythm disorder characterized by an individual's internal body clock not being aligned with the 24-hour day. 

Circadian rhythm is a roughly 24-hour cycle in a biological or behavioral process in a plant or animal. The term "circadian" comes from the Latin words circa, which means "around", and dies, which means "day", so circadian literally means "about one day". For reasons still not fully understood, natural circadian rhythms operate slightly different than 24-hours. In humans, the circadian clock usually runs slightly longer than 24 hours- 24.2 hours on average. Many studies from the 1940s through the 1960s showed that when healthy volunteers are placed in conditions without light signals, sleep patterns and body temperature rhythms begin to drift- for example, in a person with a 24.5 circadian clock, the circadian rhythms will drift about 30 minutes later each day.

All humans have a master body clock.  The master body clock is in a part of the brain called the suprachiasmatic nuclei (SCN). The SCN is a small area of the brain that sits on top of the spot where the nerves that leave the eyes come together. This location is important because it allows the SCN to receive direct light information from the eyes.

The circadian system even has its own specialized cells in the retina called intrinsically photosensitive Retinal Ganglion Cells (ipRGCs), which were only discovered about 15 years ago. These are not the rods and cones responsible for vision. Their primary role is to send light information directly to the master body clock and provide a small adjustment to keep it aligned with the 24-hour day. The master body clock then relays the message throughout the body to keep many different systems in the body on the 24-hour rhythm, including sleep.

An individual can have problems with the master body clock keeping the correct time, they could have a problem with the clock sending out the wrong signals, or they could have a disorder like Non-24 that is a problem with input to the clock – in other words, a problem where the clock is not getting the right signals.

In the case of Non-24, the master body clock may be functioning normally, however, the lack of input from those special light-sensing cells in the eye keep it from resetting to the 24-hour day. The clock reverts to its own time, which is naturally longer than 24- hours, and as a result, a person becomes misaligned with the 24-hour day.

For persons living with Non-24, their sleep-wake cycle constantly moves, so it shifts in and out of alignment with the 24-hour day. This creates times when they may be awake at night and feel the urge to sleep during the day. People living with Non-24 often find it hard to go to sleep when they want to, are unable to sleep through the night, have difficulty waking up on schedule, and may take frequent naps during the day. The timing of each person's individual clock varies from person to person, so the daily drift can range from a few minutes to an hour or longer every day.

For people with Non-24 symptoms may go through periods of getting better and worse as the master body clock shifts out of and into alignment with the 24-hour day. In the real world, where life interacts with biology, the patterns of when the symptoms become better and worse can be difficult to detect. Some people may be in temporary alignment with the 24-hour day every few weeks; for others, it could be 6-months or longer.

Non-24 is not a sleep disorder. It is a serious, chronic circadian rhythm disorder that can greatly impact your life. Persons living with Non-24 may describe difficulties with their sleep and the impact of Non-24 in their personal and professional lives differently. People generally start experiencing symptoms of Non-24 around the time they lose their light perception. A person may be impacted by Non-24 regardless of the cause of blindness or when blindness occurs.

  • Difficulty falling asleep, staying asleep, waking up in the morning, or staying awake during the day
  • Waking up tired or feeling as if you haven't gotten enough rest
  • An overwhelming urge to sleep during the day or falling asleep unexpectedly
  • Difficulties in managing school or work
  • Problems with concentration


If you think you may have Non-24, it's a good idea to speak with your doctor about it to help you manage Non-24's impact on your life. Awareness of Non-24 is very low among people living with the disorder and among health care professionals.

For some people just having an accurate diagnosis may have benefits. Often a diagnosis will involve a doctor asking questions to better understand a person's sleep history, and maybe asking that person to keep a record of their sleep. Knowing there is a recognized biological basis for the disorder may help people have discussions around symptoms with family, friends and colleagues.