system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do we have to close our eyes to sleep ?
gpt
Closing our eyes  protects them and stops them from drying out and also we don't need to be able to see when we are asleep. There are however, some people who don't close their eyes when they are asleep (and they are definitely asleep) so it is possible to sleep with your eyes open.