PD describes the horizontal position of the eyes and is not the same thing as frame size, but a larger difference between frame center distance and PD can require more lens decentration and a larger lens blank.
01 · PD
PD describes horizontal eye position
PD is a measurement related to the distance between the pupils and can be recorded as binocular PD or as separate monocular PD values.
Monocular PD is the more direct measurement when centering each lens, and it is especially important when each eye must be positioned precisely, as with progressive lenses.
Near PD can differ from distance PD, so the measurement used should match the viewing task and lens type.
02 · FRAME PD
The frame also has a geometric center distance
In the boxing system, A dimension plus DBL gives the geometric center distance of the frame, often called GCD or frame PD.
This is a geometric property of the frame, not the wearer’s PD.
The difference between frame center distance and wearer PD helps estimate how much horizontal decentration may be needed.
03 · DECENTRATION
Lens reference points are decentered to the required position
If the wearer’s monocular PD lies inward from the frame’s geometric center, the relevant lens reference point is positioned inward accordingly.
In a simple symmetric case, half the difference between frame PD and binocular wearer PD can be used as an approximate horizontal decentration per lens.
Actual ordering should still use monocular PD and account for prism prescriptions, lens design and other individual requirements.
04 · HIGH PRESCRIPTION
Frame size and decentration matter more in stronger prescriptions
If the frame is unnecessarily large or the center-distance mismatch is large, a bigger uncut lens diameter may be required.
In high myopia, larger effective diameter and decentration can increase edge thickness and weight.
In high hyperopia, required blank diameter and lens design can affect center thickness and weight, so plus and minus prescriptions should not be treated as identical.
05 · FRAME CHOICE
PD is not the only frame-selection criterion
A frame must also suit the bridge, face width, lens shape, intended use and style.
PD is an important optical factor, but it does not select a frame by itself.
Choose a frame that fits stably first, then take the lens measurements in that final wearing position.
SOLUTION GUIDE
Solutions at a glance
Compare monocular PD with frame center distance.
Consider required lens diameter together with PD and frame size.
Measure monocular PD and actual fitting height.
Check bridge, width and temple fit before focusing on PD.
GLANOS FITTING CHECK
GLANOS fitting check order
- Frame fitting
Stabilize the frame in the sequence front → bridge/nose pads → width → temple bend. - Monocular PD
Measure the horizontal position of each eye. - Fitting height
Measure in the real wearing position when the lens design requires it. - Lens selection
Consider prescription, required diameter and frame conditions together.
CAUTION
Matching PD does not make every frame suitable
PD describes one aspect of eye position. Face width, nose anatomy, frame construction and lens design can all make different frames appropriate for people with the same PD.
GLANOS EYEWEAR
There is a reason glasses feel uncomfortable.
PD · monocular PD · pupillary distance · frame PD · GCD · decentration · lens center · glasses size · high prescription