That happens to me too, sometimes. It's the most annoying thing that's ever happened to me during LDs, and I often give up trying to open them, just wandering around the dream until I wake up. Either my eyes are half-closed, only one eye is open, or my eyes are both closed (in that case, I still "know" where everything is but without being able to see them).

I tried this once and it didn't work for me, but maybe it'll work for you: ask the dream for permission to open your eyes. Or, try relaxing and not worrying about your eyes. Create a new dream scenario that will take your mind off your eyes and help you focus more on the scenery around you.