Which type of lens usually has manufacturer-engraved identification markings?

Progressive addition lenses typically have manufacturer-engraved identification markings because these markings provide essential information about the lens design and prescription. These engravings often indicate specific details such as the optical center, add power, and provide a reference for the lens curvature or design characteristics. This information is crucial for correct fitting and adjustment, as well as for ensuring that the lenses perform as intended with the progressive addition feature that allows for multiple focal points within the same lens.

In contrast, other types of lenses, while they may have some form of identification, do not generally require such detailed markings to the same extent as progressive lenses. For instance, single vision lenses primarily correct for one field of vision and may have less need for complex identification markings. Iseikonic lenses, designed for patients requiring binocular visual correction that is specific to certain conditions, may also have identifiers but not as universally as progressive lenses. Trifocal lenses, which incorporate two additional focal points alongside the single vision component, may also have identifiers, but the complexity seen in progressive lenses, which blend multiple focal areas seamlessly, leads to a greater need for engraved information to assist in precise fitting.