History
The first patent for a PAL was British Patent 15,735, granted to Owen 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 world's first commercially available PAL (Ultrifo) sold by "Gowlland of Montreal". This was based on an arrangement of aspherical surfaces.
Irving Rips at Younger Optics developed the first commercially viable blended lens in 1955 called the Younger Seamless Bifocal.
The Varilux & Carl zeiss lenses were the first PAL of modern design. It was developed by Bernard Maitenaz, patented in 1953, and introduced by the Société des Lunetiers (which later became part of Essilor) in 1959.
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 progressive addition lenses may be designed with distance to intermediate or intermediate to near prescriptions specifically for use as an occupational lens, or to offer enlarged near and intermediate view areas. Since the 1980s, 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 metrologic 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. This is why there is a difference in price.In short,the price is based on the technology used and the year the lens came to market.
Read more about this topic: Progressive Lens
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