I suppose that it is in the description of the optical viewfinder. You can set a compensatory lens so you won't require your glasses (if you wear them). The setting does in no way affect your photo. I just helps your eye to see sharp without the strain of focussing.
I believe that the diopter adjustment is just for the view finder. It basically acts like the focus adjustment on a pair of binoculars and adjust the focus for your eye. It will not affect the picture focus in any way since the camera does not use the view finder to calculate focus. If you set the camera for manual focus you must use the LCD display to set focus. Just adjust the diopter so when you look through the view finder everything look in focus.
