ZEISS progressive lenses are high-tech products. Mathematical functions are used for lens design and manufacturing – just as they are used to approximate the aerodynamic properties of an aircraft wing. To make a lens, ZEISS applies findings from its Space Technology department, which developed high-precision mirrors for the X-ray telescope on board the ROSAT satellite survey mission.
Mastering the complications involved in asymmetrical designs and leading-edge optical surfaces – this is just a way of life in the production of progressive lenses at ZEISS Vision Care. Every lens is unique and must be exactly calculated on the basis of the data measured by your optician. The goal is to provide your constantly moving eyes with the optimum correction to ensure maximum visual comfort: in the near, intermediate and distance viewing zones.
12,000 individualised progressive surfaces are currently produced every day at the ZEISS production facility in Aalen, Germany, and each and every one is tailored to the personal needs of the wearer. This requires a vast amount of computation. Thanks to the expertise of the company's employees – which include many mathematicians and physicists – software tools specially developed by ZEISS and powerful computer technology are used to calculate individualised lenses exactly and precisely in a matter of seconds. In the early 1980s, an entire night was needed to design a freeform lens surface.
Progressive lenses are true masterpieces of optical technology. The upper part of the progressive lens is used for distance vision, and the lower part for near. The area between these two zones – is called the transition zone or the progression corridor – and ensures you enjoy clear vision in the complete viewing range from distance to near. The laws of physics inevitably lead to slight blurring in the periphery of this zone. The extent of this blurring depends on the quality of the progressive lens and on the degree of individualisation. The general rule is: the better the lens is tailored to the personal needs of each individual wearer, the less the peripheral blurring becomes. This decisively improves visual quality and wearer tolerance - and delivers the most natural vision possible.
ZEISS launched one of the first individually tailored lenses with the name Gradal® Individual on the market in 2000. This was a milestone in the history of optics. Then as today, the calculation and production of the lens incorporate not only the prescribed powers for the various ranges of vision, but also the personal parameters of the wearer such as the distance between the pupils, the fit of the frame on the face, the reading distance and other wearer parameters. This method of mathematical design and production has been constantly optimised over the years. These technological advances have been aided not only by faster and better methods of computation and production, but also by ongoing advanced research and development work at ZEISS. Only in this way has it been possible to produce a progressive lens surface with micrometre precision.
Every progressive lens surface is what is known as a freeform surface. This is made up of tiny surface elements that are locally variable but together create a smooth progressive surface. These elements are then mathematically adapted to the measured personal data of the wearer. This allows optimum matching of the vision zones to each wearer's personal needs, therefore simultaneously enhancing wearer tolerance to the lenses.
You can't tell whether a spectacle lens is individualised or "off-the-shelf" by just looking at it. So where does the difference lie? Which spectacle wearers have the most to gain from individually optimised lenses?