Accurate lens measurement starts before any number is recorded. The selected frame needs to sit in the position in which it will actually be worn, otherwise the coordinates measured on that frame can shift later.
Fitting height and position-of-wear values can change when a frame slides a few millimetres, tilts or rotates. PD describes the wearer’s eye position, but the way that eye position is transferred into a particular frame still depends on how the frame sits.
Pre-adjustment is therefore not the same as the final delivery fitting. Its purpose is to create a stable, repeatable wearing position before optical measurements are taken.
01 · PRE-ADJUSTMENT
Create a stable reference position before measuring
A new frame can already be twisted or uneven from display, shipping or handling. Measuring it immediately makes it harder to separate frame distortion from the wearer’s natural facial asymmetry.
Check the frame front, bridge or nose-pad contact, overall width and temple support so that the frame settles naturally and does not immediately slide, rotate or lift when the wearer moves.
02 · HORIZONTAL DATA
PD belongs to the wearer, but lens placement belongs to the wearer and frame together
Distance PD or monocular PD does not change simply because the frame is moved a little higher or lower. It describes the horizontal position of the eyes.
However, lens centration is calculated inside the selected frame using its bridge and lens geometry together with each eye position. In an asymmetric fit, separate monocular values provide more useful information than simply halving one binocular PD.
03 · VERTICAL DATA
Fitting height changes directly when the frame position changes
Fitting height records where a pupil or manufacturer-defined fitting point falls vertically inside the lens shape. If the frame is measured while it is sitting several millimetres lower than its normal position, the recorded height will represent the wrong condition.
This matters especially for progressive lenses, where the fitting cross is tied to the intended viewing zones. Some individualized or high-power single-vision designs also use vertical eye-position data.
04 · POSITION OF WEAR
Measure vertex distance, pantoscopic tilt and wrap when the lens design requires them
Some individualized single-vision, progressive and high-wrap lenses use back vertex distance, pantoscopic tilt and face-form or wrap data as design inputs. These values change when the frame adjustment changes.
Not every conventional single-vision lens requires all three values. The correct approach is to identify which measurements the specific lens and ordering system require and then record them consistently in the actual wearing position.
05 · AFTER MEASUREMENT
Large fitting changes after measurement require a recheck
If nose-pad height, temple bend or frame tilt is changed substantially after measurement, the original fitting height and position-of-wear values may no longer describe the finished glasses.
Small comfort adjustments are normal at delivery, but when the optical position changes noticeably, the relevant measurements should be checked again instead of assuming the earlier numbers still apply.
06 · LENS TYPE
The same fitting principle is used differently by different lens designs
For a conventional single-vision lens, prescription and horizontal centration are often the main optical inputs. Progressive lenses commonly require monocular distance PD and fitting height, while individualized designs may add position-of-wear data.
The principle of stabilizing the frame first remains the same, but the number and precision of measurements depend on prescription, frame geometry and lens design.
SOLUTION GUIDE
GLANOS measurement and fitting check
Remove obvious twist before measuring.
Establish where the frame naturally rests on the nose.
Reduce sideways movement and slipping.
Record PD, fitting height and any required wear parameters.
Repeat relevant measurements after a major fitting change.
GLANOS LENS CHECK
Measurements are coordinates created by the wearer, frame and lens together
A precise number loses value if it was measured in one frame position and the finished eyewear is worn in another. Pre-adjustment keeps those two conditions as close as possible.
CAUTION
Do not force a frame into an arbitrary angle just to hit a target number
A manufacturer recommendation may define a design range, not a universal fitting rule. Eyelash or cheek contact, bridge support, stability and comfort still need to be respected.
GLANOS EYEWEAR
Eyewear discomfort has a reason.
eyeglass fitting · lens measurement · PD · fitting height · vertex distance · personalized lenses