be (as) blind as a bat
1. slang To be unable to see at all. After neglecting his vision for years, my grandfather became blind as a bat, unable to even see shadows.
2. slang To have poor vision. I've worn glasses for 20 years, so I'm as blind as a bat now. That's not a cat, it's a trashcan! Geez, you really are blind as a bat!
3. slang To be oblivious to something. Are you blind as a bat? Those two have been flirting all afternoon!