Well since its near impossible to enter sleep paralysis with your eyes open, it's much better to do it with eyes closed. During SP, its also better to keep your eyes closed, because opening them might break the SP and send you back to square one. And if you are attempting to lucid dream from the SP, eyes closed is the way to go so you can see your dream world visualize and you will end up opening your "dream eyes" once you have successfully transitioned into the dream. Most of the time, you will know when you have entered the dream.