Precise progressive design can involve more than prescription and PD.
Vertex distance, pantoscopic tilt and face-form or wrap angle describe how the lens is positioned relative to the eye.
01 · VERTEX DISTANCE
Vertex distance relates to the lens-to-eye distance
Changing the distance between the spectacle lens and cornea can change effective power, with larger effects at stronger prescriptions.
Back vertex distance describes the separation between the back surface of the spectacle lens and the eye. Changes matter more as prescription power increases, and in personalized designs the value can also contribute to the geometry used to calculate how rays reach the eye.
02 · PANTOSCOPIC TILT
Pantoscopic tilt describes vertical lens inclination
Many frames tilt so the lower lens edge sits closer to the face. This changes the angle at which the wearer’s line of sight passes through the lens.
Pantoscopic tilt describes the vertical inclination of the lens in the worn frame. Once a powered lens is tilted, the line of sight no longer meets it at the same angle, so effective sphere, cylinder and peripheral optics can change more noticeably as power and tilt increase.
03 · FACE FORM ANGLE
Face-form angle describes how the frame wraps around the face
Frames can curve inward toward the temples, especially wrap and sports styles.
Face-form or wrap angle describes how the two lenses curve around the face horizontally. The effect may be small in ordinary frames, but high-wrap sports frames create larger oblique viewing angles and may require more careful optical compensation.
04 · TILT EFFECT
Tilting a powered lens changes the optical conditions along the line of sight
Using a lens at a different angle from the design reference can alter effective sphere/cylinder components and off-axis optical behavior. The magnitude depends on power and angle.
The existence of tilt effects does not mean every frame requires a special personalized correction. Prescription magnitude, actual angles and lens design all matter, and some products use assumed default wearing values. The key question is whether the chosen lens actually uses the measured parameters.
05 · PERSONALIZED DESIGN
Some individualized lenses use these parameters in optimization
Certain freeform or personalized progressives calculate performance in the actual wearing geometry. Not every progressive requires the same inputs.
Some individualized progressives accept vertex distance, pantoscopic tilt and wrap as order inputs and optimize the surface for the worn position. Other progressives do not require those measurements. More input fields should not be treated as a quality grade by themselves.
SOLUTION GUIDE
Solution guide
Check the wearing parameters requested by the design.
Measure in the final fitted position.
Confirm whether wrap is incorporated in the design.
Supply the measurements the product actually uses.
GLANOS LENS CHECK
Finish the frame fitting before measuring position of wear
Vertex distance, pantoscopic tilt and wrap angle are meaningful only in the final intended wearing position.
CAUTION
More measurement inputs do not automatically make a lens better
What matters is how the selected design actually uses those data for optical optimization.
GLANOS EYEWEAR
There is a reason glasses feel uncomfortable.
vertex distance · pantoscopic tilt · wrap angle · progressive lenses · individualized lenses · fitting