I wouldnt because of the sand/debris in the water.....
I'm not by the ocean or anything, just curious. Is it safe to open your eyes in seawater?
I do. It stings at first but gets more comfortable as time goes on.
You can, but the salt stings a bit. Just remember that besides sand, our oceans are polluted. There's also bacteria in the water. Most prefer goggles, but people have been opening their eyes without masks for millennia. Your choice. I don't.
I have. Sometimes you need to get your bearings after being knocked underwater by a wave. You need to head towards the light.
Not in long stretches. There are many unpleasant things in ocean water that can possibly damage your eyes.