Because they lack photic input to the circadian time keeping system, people who are totally blind have body rhythms that are not necessarily synchronized to the 24 hour solar and social day. Insomnia is the most common sleep complaint of people who are blind. A free running clock goes by a 24 hour, plus thirty minute cycle daily. It is an additional 30 minutes off with each successive day. Some days the patients have symptoms and other days there is no problem.
Most patients attempt to sleep and arise at conventional social times.
This produces progressively less sleep, with secondary daytime sleepiness interfering with functioning at work or at school. In addition, sleep may be skipped for 24 to 40 hours, followed by sleeping for 14 to 24 hours without awakening. Since body temperature is regulated by body clocks that respond to the day, night cycle, there is a connection between temperature and sleep patterns. If people fall asleep when their body temperature is falling, they will have long bouts of sleep, but if they go to sleep when their body temperature is rising, their sleep will be short. Treatment follows two strategies.