I recently did a ride in light-moderate rain, and I used a Gore-Tex helmet cover. I wore it on a helmet with a visor, and it covered the whole thing. I found that the rain just dripped off the front, far enough from my face to keep the water out of my eyes.

I don't know how well it would work in heavy rain. I hope it's a long time before I find out, since I'm not a big fan of riding in those conditions.