I just asked my doctor to prescribe these lenses for me simply due to the fact that on occasion I have been known to fall asleep while reading. (I run a business and am a student) I was trying for the highest oxygen permeability just in case. If I were to fall asleep with them on, I would definitely stick to glasses the next day to make up for lost oxygen.

What I have now are monthly disposables rated up to 7 days continuous. Even though I do realize that occassional overnight wear would not be the end of the world, I would prefer to use something at the highest rating for optimum safety.