Blind people know when they wake up mainly through non-visual cues such as sound, touch, sense of gravity, and changes in their environment, like temperature or the feeling of bed covers. They may also use alarms or other devices to help signal the time to wake up. Additionally, many blind people have functioning retinal ganglion cells that detect ambient light for regulating circadian rhythms, so those with some light perception can align their sleep-wake cycle to day and night even without seeing images. However, totally blind individuals without light perception may experience circadian rhythm disorders that can impact their sleep patterns. They typically rely more on behavioral cues and devices to regulate waking time.
