Well, maybe some people think blind people sleep with their eyes open. But on the other hand, according to some researches, blind people sleep with their eyes closed because eyelids are controlled by muscles which relax and close when you sleep. And it is just like the normal person. So that is not kind of weird.
Sleeping with the eyes open is the habit. Some blind people still open their eyes when they sleep, while others will not. I have met such person before who scares me a lot. Then I hear the nasal sound and know he is sleeping. Actually a lot of people who are not blind still open their eyes to sleep. They have some kinds of problems at the eyes.
The majority of the blind sleep with their eyes closed. A little number of them sleep with eyes open. It varies from individual to individual. Some blinds get illness in their corneas and lens. So the function of blinking and moisture is unsound. Some blinds just have sight impairment and the other nerves of their eyes just as normal as the healthy man. And i have never met a blind who sleep with eyes open.
However, some healthy people sleep with eyes half-closed. What's more it's genetic not a sick. Such as Zhang Fei, a person in a Chinese film classic the Romance of Three Kingdom. There are also some other reasons for half-closed eye. First, acute facial neuritis. Second, deformed orbicularis oculi. Third, eyes with severe proptosis due to some diseases such as intraorbital tumors and hyperthyroidism. Though these people sleep with eyes half-closed, their eyeballs are covered by their eyelids and just a part of the white one are visible. So their eyes are not undeveloped film to light and it can not affect sleep heavily.
Even blind people can not sleep with their eyes open. If the eyelids do not close when people are sleeping, the bacteria will get into the eyeballs and corrode them, and then the corrosion will be transmitted to the nerves of the eyes, thus damaging the eyes. However, in some cases, some people will half open their eyes when they are asleep. There are mainly two reasons for it. First of all, these people have insufficiency of the spleen caused by disorder of diet, disorder of working and resting, or long time of disease. The other people who sleep with half open eyes may be born to sleep in this way. In this case, people should make sure that their sleeping environments are dar enough, and the darker, the better. Becuase the darkness can do less damage to the eyes when people are asleep. The function of eye opening and closing are completed by the extraocular muscles and mimetic muscles, especially through the shrinkage and relaxation of the levator palpabrae muscles and the orbicularis oculi muscle. If the nerves have very weak control to the muscles when people are sleeping, or if the orbicularis oculi muscles have low tension, or if the levator palpabrae muscles have weak contraction, it can be hard for the eyes to be closed completely. Some diseases can also lead to incomplete close of eyes, such as acute facial neuritis. If so, people should go to the doctor's as soon as possible in can that the conditions get worse.