It depends on why its blind, but if you move your finger really close to any animals eye, they will not close it if they are blind. They will also not reach for a plant if you put it really close to them. A small chameleons pupils might be too small, but if you hold a bright light up to their eyes and the pupils stay dilated they are blind. I wouldn't suggest holding a bright light next to their eye, but it's a way to tell.