The reason why some babies sleep with their eyes open is still unknown because there is no research established on this phenomenon. However, it can be associated with the fact that babies spend more time in REM sleep and the lasting time of this condition accounts for 50 percent of their overall sleep time. REM is a more active sleep cycle in which eyes will open during sleep. This phenomenon is harmless and does not indicate sleep problem. It is also very common among infants even though it can last until 12 to 18 months. Parents can simply stroke the eyelids closed if this bothers them a lot. If this still lasts when the baby are elder than 18 months or his eyes open for too long at a time, the parents should consult a pediatrician.
It's funny that babies sleep with their eyes open, but if it happens all the time, you should take this seriously. The most essential reason to give rise to this situation is babies eyes are too big or their eyelids are too short. While they are sleeping, the muscles around eyes are absolutely relaxed and their eyes will open naturally. Besides, there are also some diseases that will stem from this problem. The open eyes is quite a normal phenomenon in babies. However, it will get the invisible bacterium easily which will be bad for the eyes. The next day the eyes may get infection and dryness. Therefore, for the sake of your babies health, you'd better ask a professional ophthalmologist for some advice.