From Wikipedia, the free encyclopedia
The first patent for a PAL was British Patent 15,735, granted to Own Aves with a 1907 priority date. Aves' patent included the progressive lens design and the manufacturing process. However this was unlike modern PALs. It consisted of a conical back surface and a cylindrical front with opposing axes in order to create a power progression. This design was never commercialized.
While there were several intermediate steps (H. Newbold appears to have designed a similar lens to Aves around 1913), there is evidence
to suggest that Duke Elder in 1922 developed the worlds first commercially available PAL (Ultrifo) sold by "Gowlland of Montreal". This was based on an arrangement of aspherical surfaces.
The Varilux lens was the first PAL of modern design. It was developed by Bernard Maitenaz, patented in 1953, and introduced by the Société des Lunetiers (now called Essilo) in 1959. VAR is currently the most widely sold progressive lens brand worldwide.
Early progressive lenses were relatively crude designs but modern sophisticated progressive lenses have gained greater patient acceptance and include special designs to cater to many separate types of wearer application: for example lenses may be customized for use with computers, or to offer enlarged near and intermediate view areas. Over the 1980s through today, manufacturers have been able to minimize unwanted aberrations by:
- Improvements in mathematical modeling of surfaces, allowing greater design control.
- Extensive wearer trials.
- Improved manufacturing and lens metrology technology.
Today the complex surfaces of a progressive lens can be cut and polished on computer-controlled machines, allowing 'freeform surfacing', as opposed to the earlier casting process.