A pair of glasses standing side-on in silhouette, the lens front leaning in at the bottom.

Measuring and fitting

Pantoscopic tilt

Optical glossaryMeasuring and fitting

The forward tilt of a frame relative to the face. Individualized designs account for it; standard designs assume an average.

Three measurements of how a frame sits: vertex distance, the gap from lens to eye; pantoscopic tilt, how far the lens leans in at the bottom; and wrap, how far the frame curves round your face.

Illustrative · the shape of the principle, not measured data

In more depth

Seen from the side, most frames lean the bottom of the lens in toward the cheek. That forward tilt keeps the lens roughly perpendicular to the eye as it drops to read, and puts the reading zone closer to the eye where it is used.

Tilt changes the power the eye receives, adding a little unwanted cylinder and sphere as it grows. Standard designs are calculated for a typical tilt; individualized designs take your measured tilt and recalculate the surface so the power you receive matches the power prescribed.

Related terms

Vertex distanceThe gap between the back of the lens and your eye. At strong powers, a change in this distance changes the effective prescription.Wrap angleHow much a frame curves around the face. High-wrap sports frames need designs compensated for it.Freeform surfacingManufacturing in which a lens surface is cut point by point by a computer-guided tool from a map calculated for one order, rather than molded. On made-to-order CLIFF lenses it is the back surface — the surfacing and the design both — on every made-to-order tier. Versatile, the stock lens, is molded, not freeform.

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