Why Is The Vision The First To Go?

I have always heard the vision is the first to go. I never understand what in the world that meant until recently I was standing in a store looking at some directions and no matter how I turned my head I couldn't make the words come in clear. I was getting very frustrated and suddenly this older woman tapped me on the shoulder. Without saying a word she took her glasses from around the little rope on her neck and placed the glasses around her eyes. She then took the bottle from me and began reading the directions. After completing the directions she quietly looked at me and said:" Sweetie dont' you know the eyes are the first to go!"