A lens surface in raking light, revealing two tiny etched circles.

Making and checking a lens

Engraving

Optical glossaryMaking and checking a lens

Permanent laser markings applied at manufacture, readable under angled light. Every stock lens and every progressive lens carries the CLIFF mark — the CLIFF icon, or the letters CLF.

A progressive's permanent marks, found under angled light: two alignment marks that locate the fitting cross, with the CLIFF mark and the addition beside them. Layout is typical, not exact.

Illustrative · the shape of the principle, not measured data

In more depth

Progressive lenses carry small, near-invisible laser marks. Two alignment marks a standard distance apart let an optician find the fitting cross and the lens's orientation again after the temporary ink markings are wiped away; nearby marks identify the design and the addition.

They are best found by holding the lens against a light background and tilting it under a lamp. Every stock lens and every progressive lens carries the CLIFF mark — the CLIFF icon, or the letters CLF — so the lens itself records who made it.

Related terms

Progressive lensA lens whose power changes gradually from distance at the top to reading at the bottom, with no visible line.Fitting heightThe vertical distance from your pupil center to the bottom of the lens in your chosen frame. The most common cause of progressive remakes when wrong.DispensingThe professional work between prescription and finished glasses: frame selection, measurement, fitting, and adjustment. Where most of a lens's real-world performance is decided.

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