Sr. Crayon replied accurately according to my understanding. We have our eyes open during salah and our focus is the point where our forehead touches the ground upon sujud, or prostration. I think it is a matter of following the Sunnah of Muhammad (saaws) and to aid us in concentration and focus during salah.
As a reminder we also place a sutra, or object, before us and don't let a person or animal pass between us and the sutra during salah. The sutra serves as a barrier beyond which people can pass in front of us.