Two people can both wear -5.00 D lenses, or an old and new pair can have the same prescription, yet the edge thickness can differ substantially.
One key variable is how far the farthest frame edge lies from the optical center.
01 · EFFECTIVE DIAMETER
The required lens diameter can change
Edging does not depend on frame width alone. The uncut lens must cover the farthest part of the frame from the optical center, so frame shape and eye position change the effective diameter required.
The finished lens must contain enough material to cover the entire frame shape around the intended optical center. That makes the farthest point of the shape from the optical center more important than frame width alone. Two frames with the same A-size can require different blanks and finish at different thicknesses if one has long corners or a deeper shape.
02 · FRAME SIZE
In myopia, retaining farther peripheral lens means more edge thickness
Minus lenses become thicker toward the edge. A smaller frame removes more thick peripheral material; a larger frame keeps more of it.
A minus lens generally becomes thicker as distance from its center increases. Large shapes or distant lower and outer corners therefore retain more of the thick peripheral lens. This is why a smaller, well-centered frame can have a major cosmetic advantage in strong myopia: it removes peripheral material that would otherwise remain in the finished lens.
03 · PD & DECENTRATION
More decentration can require a larger blank
When pupil position differs substantially from frame geometry, the optical center must be shifted, increasing the required diameter and potentially the edge thickness.
When the wearer’s pupil does not line up with the geometric center of the frame, the lens optical center has to be decentered toward the pupil. More decentration can require a larger blank and more peripheral lens on the opposite side. Two people with the same prescription and the same frame can therefore end up with different required diameters and edge thicknesses because their monocular PDs differ.
04 · FRAME SHAPE
Shape matters even when horizontal size is similar
Round and square shapes can place the farthest edge at different distances from the optical center. Corners of a square frame can be particularly far out.
Shape matters beyond horizontal and vertical dimensions. A long square corner, the lower sweep of a Boston shape or the upper extension of a cat-eye can become the farthest point from the optical center. In strong prescriptions, looking at where the pupil sits inside the actual outline is more useful than choosing a frame from nominal size markings alone.
05 · INDEX & DESIGN
Material and design also change the result
Higher-index material and aspheric design may reduce thickness, but their effect works together with frame shape and eye position.
Index, base curve, spherical or aspheric design and minimum-thickness rules continue to affect the result after geometry is set. Higher index can reduce thickness, but a large frame and heavy decentration can give back much of that gain. Thickness control therefore works best when frame geometry and material choice are optimized as one system.
SOLUTION GUIDE
Solution guide
Avoid unnecessary size.
Avoid extreme decentration where possible.
Consider the farthest edge, not width alone.
Choose an appropriate refractive index.
Compare aspheric options when useful.
GLANOS LENS CHECK
The same prescription does not guarantee the same thickness
Finished thickness is the result of prescription → optical center → frame shape → effective diameter → material → design → edging. In this lens series, index, material, design and coating are not treated as independent quality grades; each is evaluated in the context of prescription, frame geometry and actual wearing conditions.
CAUTION
Do not sacrifice frame fit and vision only to reduce thickness
A lens that suits the wearer and prescription comes first. Material chemistry, design rules, minimum thickness and coating architecture vary by manufacturer and product, so a value or feature from one lens should not be generalized to all spectacle lenses.
GLANOS EYEWEAR
There is a reason glasses feel uncomfortable.
lens thickness · effective diameter · high myopia · PD · frame size · high index