PD is often thought of as one number describing the distance between the two eyes.
For progressive lenses, the right and left pupil positions are usually more useful when measured separately because faces and eye positions are not perfectly symmetrical.
01 · BINOCULAR PD
One number describes the total inter-pupillary distance
A binocular PD of 64 mm does not guarantee that each side is exactly 32 mm relative to the frame or bridge.
Binocular PD gives the total distance between the pupils but does not tell us the individual distance from the frame center to each eye. When the face is asymmetric, dividing the total exactly in half can place one or both lenses differently from the real monocular positions.
02 · MONOCULAR PD
Each eye position is measured individually
Values can differ, such as 31 mm on one side and 33 mm on the other. What matters is where each pupil lies relative to the worn frame and bridge.
Monocular PD positions each eye horizontally relative to its own lens design. This is especially useful when the frame or bridge does not sit perfectly symmetrically on the face, because optical placement should follow the actual pupils rather than the geometric center of the frame.
03 · PROGRESSIVE DESIGN
Each eye should use the intended progression path
If a lens is decentered horizontally, the eye may move through unintended parts of the progressive design.
Horizontal misplacement in a progressive lens can move the eye away from the intended corridor and toward areas with more peripheral aberration. The effect is not limited to distance centration; the path used through intermediate and near also shifts, which is why monocular PD matters more in this design.
04 · INSET
Near gaze moves inward
During near viewing the eyes converge, and the near zones of progressives are commonly inset accordingly.
Inset is not one fixed number: design, prescription, working distance and wearer conditions can influence it.
Near inset reflects the inward rotation of the eyes when viewing close targets. It is not necessarily a single fixed value: depending on the product, distance monocular PD, working distance, add, prescription and design algorithm may influence where the near zone is placed.
05 · FRAME POSITION
The frame itself may not sit perfectly symmetrically
Nose and ear asymmetry can alter how the frame sits, so monocular measurements represent real wearing geometry better than simply halving binocular PD.
Even an accurate monocular PD loses value if the frame later slides down or shifts to one side. Measurement and frame fitting are therefore part of one process: stabilize the frame on the face, measure from that position and preserve it through ordering and final delivery.
SOLUTION GUIDE
Solution guide
Reflect actual right-left pupil positions.
Position each lens separately.
Improve alignment with the intended corridor.
Avoid assuming that every wearer has the same geometry.
GLANOS LENS CHECK
PD is not just an isolated number
Accurate monocular PD must be considered together with where the chosen frame actually sits on the face.
CAUTION
Do not automatically divide binocular PD by two
Meaningful error can result when right and left pupil positions are asymmetric.
GLANOS EYEWEAR
There is a reason glasses feel uncomfortable.
monocular PD · PD measurement · progressive lenses · pupillary distance · multifocal lenses · eyewear measurement