Interesting subject.
Way back when...I was in the Navy. One of the exercises we did was learning to move about the ship in complete darkness. You would be surprised just how dark it can get inside a metal ship at sea at night. We would do this in case of emergency.
Ever since then, I have made a habit of closing my eyes and making a "mental map" everywhere I go. It sounds strange to do this but it has saved me on more than one occasion over the years.
Vision is one of our most relied upon sences. Because it is always there we take it for granted. Almost everything we do as humans, we do by sight. This is why when a person losses their sight it is so hard for them. With practice, they eventually learn to do just about what ever they want.
Until recently, I didn't lose my balance when my eyes were shut. As my PD has advanced and my balance has become worse I can't close my eyes with out losing my balance.
The human body is sooo wierd.

GregD