How Do You Calculate Decentration?

The total decentration can be calculated by subtracting the patient's PD from the frame PD. This measurement assumes that the patient's face is perfectly symmetrical. Monocular decentrations can be calculated by taking monocular PD measurements and subtracting from half the frame PD.

What is Decentration of a lens?

Lens decentration equals the difference of the distance between the optical center and pupil distance. Though this could lead into various visual problems, it had not been taken into consideration since measurement on pupil-distance rarely conducted while producing spectacles.

How much Decentration is too much?

A good rule is to limit decentration to 1 to 3 millimeters whenever you can. In high minus powers, excessive decentration thickens the lateral edge of the lens. In plus, excessive decentration thickens the nasal edge of the lens and makes the magnification of the patient's eyes greater.