Blind people sleep less

Life according to the internal clock

High level of suffering

"For those affected, a high level of suffering arises from the fact that they have to constantly adapt to their own internal clock in everyday social and professional life," explains Fietze. "Symptoms such as insomnia and excessive daytime sleepiness are the result." Patients are hit hardest in phases when their biological day coincides with the exogenous night. During this time they sleep little and poorly and are accordingly tired, rested and only partially productive during the day.

"In contrast to other sleep disorders, in which those affected mostly cannot sleep during the day, patients with non-24 periodically have to fight against falling asleep every day," says the expert. Doctors also speak of an intermittently pronounced sleep disorder, as this occurs episodically and fluctuates in strength. Patients are often only symptom-free on days when the 24-hour day and their internal circadian rhythm run almost parallel.

The non-24 disorder of many completely blind people is often not even known to sleep doctors. It can therefore be assumed that many of the patients are undiagnosed. In order to determine the disease, a specific questionnaire is used in addition to a careful sleep history. In addition, patients should keep a sleep diary for a few weeks to months. This enables the doctor to recognize the individual sleep-wake pattern.

Another method is actigraphy, in which data about movements and sometimes parameters such as brightness and ambient temperature are recorded in order to determine activity and rest cycles. To do this, the patient wears a measuring device that resembles a wristwatch for a few weeks. In some cases, doctors will perform polysomnography or melatonin tests to differentiate other types of sleep disorders. The epiphyseal hormone melatonin is a marker of the circadian rhythm and is released by the body depending on the internal clock (see box). The highest concentration is found in the biological night, while it is only present in extremely small traces in the hours of the biological day.