The "optical centre" of a lens element is a difficult concept. Real lenses of real thickness have two principal planes each defined by an array of principal points. The two principal points/planes exist because light can be sent through a lens from either direction. One could think that the intersection of the optical axis and a principal plane is an "optical centre" but then there are two "optical centres". This esoteric stuff is irrelevant for a lens focussed by adjustment.