Free form spectacle lenses: A new technical report

Ronald Rabbetts describes and a new report from the British Standards Institute that clarifies the terminology surrounding free form lenses

BSI has published a technical report on free form lenses: PD ISO/TR 18476: 2017 Ophthalmic optics and instruments – Free form technology –Spectacle lenses and measurement. This 30-page document is divided into five main sections: a short technical introduction, manufacture, the potential benefits of free form lens calculation and measurement and quality control.

Although single-vision free form lenses are used in, for example, sports spectacles that have significant as-worn face form (wrap) and pantoscopic angles, the text relates to progressive-power lenses since these are the most common free form ones.

Annex A shows a flow diagram of spectacle lens dispensing; this compares the process for standard lenses, free form lenses that have been specifically designed to take account of just the spectacle frame parameters, and free form personalised lenses. Annex B goes into greater detail on the measurement and quality control while Annex C is a glossary of terms.

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