Blind individuals who have had their eyes removed can experience cyclical sleep problems, indicating a disruption in entrainment to the light-dark cycle.

“I hear from a number of blind people, a lot of them have issues with sleep. I think in part because they don't realize that they too need to see light at particular times of day or night in order to match their their schedule.”

“And this is actually one of the things that blind patients often complain about if they've got retinal blindness is insomnia and uh their brain's awake in the middle of the night. Exactly. They're not synchronized.”

“So blind people who can't see light, they get this, their natural rhythm never gets reset. So it's slightly more than 24 hours. So if you were living a slightly more than 24-hour rhythm, you woke up at 6:00 today, you'd wake up at 6:30 tomorrow, you'd wake up at 7 the next day, and then eventually you're waking up at 2:00 in the afternoon. It's miserable. And then it cycle around. It's called It's called non 24-hour circadian rhythm disorder.”