Free-form lenses have their surfaces digitally manufactured, allowing point-to-point surfacing in which the lens surface curvature can be controlled over thousands of individual points. 

In order to dispense a pair of free-form progressive power lenses (PPL), there are several measurements that need to be included, in addition to what is normally expected for a traditionally manufactured PPL. 

This article covers the manufacturing process of free-form progressive lenses, including the specialist measurements required and the relationships between these measurements. In addition, non-tolerances are discussed and trouble shooting advice is offered to reduce these in practice.

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