I don't know about PD and OC, but where I go they measure all sorts of ways and I do know they measure from bottom of frame up to some point on the eye. Would that be OC?Where I went wrong was using LensCrafters for my glasses when I first started wearing them. They measure PD of course, but they also center your eyes in the lenses using OC. I don't remember what the acronym stands for, but it's the vertical measurement of your pupil in the lens. PD is the horizontal measurement.
It's been my experience that no one, even other companies under the LensCrafters umbrella, use this.
My eyes are used to this type of lens so it's a big hassle buying glasses. Like I said before, the last 2 times I bought glasses they each had to be remade 3 or 4 times. Anyone else had this issue?