Progressive lenses are manufactured using a combination of mass-produced semi-finished blanks and computer-controlled precision surfacing to create the custom prescription on the back surface.馃彮
Mass Production:
Creating the Semi-Finished Blank The complex progressive surface (the corridor) is mass-produced on the front of the lens using cast polymerization:路
Mold Assembly: A glass mold with the progressive curve is paired with another mold and held together by a gasket or tape.
Casting: A liquid plastic monomer (like CR-39) is poured into the cavity and cured in an oven .路 Result: This produces a “blank” with a finished front surface but a thick, unfinished back surface .馃捇
Customization: Free-Form Surfacing To fulfill your specific prescription (including cylinder and prism), the back surface is machined:路
Digital Design: Software calculates the exact 3D shape needed to work with the front progressive curve .路
Precision Machining: A CNC generator mills the back surface, followed by fine turning and polishing .路
Prism Thinning: To keep the lens thin, the back surface is often tilted or cut asymmetrically to distribute thickness more evenly .
馃И Alternative Methods路
Glass Lenses: Historically made by heating a glass blank until it sags into a progressive mold using vacuum pressure .路
Injection Molding: Used for some materials like polycarbonate, where hot polymer is injected into a precision mold .
Are you interested in the specific materials used, or how the “corridor” design is digitally calculated?