There are Red Eyes, to signal evil, there are glowing eyes, to signal power, there are even eyes which never open, to signal wisdom or trickery, there are even Blue Eyes, which can signal lots of things depending of who you ask. Then there are characters whose eyes are covered to the point it seems they have none, to signal... that they don't have anything to signal at all. A good way to define a soldier as being "another mook" or "someone who is not important to the plot" is to have the shadow from their helmet cover their eyes, to the point where it seems they don't have eyes at all. This is due the fact eyes are usually the most expressive part of a character, which is why cartoons usually make them bigger than they would be in real life. Taking away this expression, it's easier to convey that the character doesn't have a very significant personality. Of course, there are exceptions. Compare Faceless Goons for when the whole face is covered. See also Blinding Bangs Do We Have This? Seen it millions of times. Also, if someone can make the captions work go ahead.
Hello, Unknown Troper. You'll need to get known to lend a hand here.