Aliens don't have eyes. However, an interesting fact to point out is that, if you look at a Drone's skull, it has a human-like front with eye-sockets, nose hole and everything up until the mouth area. It isn't used for anything, obviously, but why they have it is unknown.
It's best seen on Giger Drone busts and Titan's drawings, as he seems to include the human skull-like design not seen anywhere but the Grey, and even then many portrayels of the legendary beast exclude that tiny detail.
It's always bothered me as to why it's there. It could be just another "just 'cause" thing Giger decided to throw on to add to the mysteriousness or just for the hell of it. If I come across a clear picture I'll post it.
EDIT:
Here's a picture of the
Grey's skull.
By
Dan Luvisi, one hell of an artist. He's also done a Jungle Hunter portrait and a marine portrait, both easily found by clicking the links in the description of the Drone.