Progressive lenses made their commercial debut in the middle of the last century. Also known as progressive addition lenses (PAL), the lenses enable eyeglass wearers to transition from distance to near vision without the image jumping when the eyes shift from one distance zone to another. They also have a cosmetic benefit: there is no line as there is with bifocals.
In the past, producing these lenses was no easy feat. The traditional process required a semi-finished lens with a standard front. The prescription would be ground onto the back surface with a generator. Calculating the geometry to impart on the lens involves complicated mathematics. “You can imagine doing this without Excel spreadsheets to do all of your calculations,” says Dennis Fong, OD, clinical instructor at the UC Berkeley School of Optometery. “Everything was originally done by hand and then you see pictures of these old generators that made forms and then you use the forms to create the complex curvature.”
