A prescription job starts with a semi-finished blank chosen by material, base curve and design. In the laboratory the blank is blocked, cut on a generator (free-form CNC for digital designs), polished, cleaned, hard-coated and AR-coated, then edged to the frame shape on a tracer-guided edger and mounted. Large labs do this for thousands of jobs a day on automated lines from Satisloh, Schneider, OptoTech and Nidek.
Free-form surfacing allows the whole design to be cut on the back surface, so any progressive design can be produced from a plain semi-finished blank. It moved value from blank makers to lens designers and labs.
Every job is checked on a lensmeter against the prescription within ISO 21987 tolerances, and inspected for coating defects, cosmetic marks and correct edging. Remote edging — the lab edges and ships a finished lens for a store or online retailer to mount — is now standard.