Progressive lenses are high-tech products. The starting point in the development of a progressive lens is the goal to achieve a certain power design – either for allround use or for special visual tasks, e. g. a computer workstation.
To create a new power design, a system of equations with several hundred unknowns and possibly several thousand equations must be solved. Extremely complex spline functions are required to design the power structure of progressive lenses.
However, this computation process alone does not suffice to create a new power design. The optical designer has to adapt the computed surface constantly to the desired surface – a process known as iteration. The extremely intricate mathematical calculations required to create a new progressive surface can only be mastered by the use of state-of-the-art computers.
If mathematicians still had only the same aids at their disposal as were available 50 years ago, it would take them 27 million years to find the solution to a single stage in the iteration process!
In the production of progressive lenses, a special freeform generator transfers the newly computed power design to the semi-finished lenses or casting dies.
Complex production trials are required to manufacture the first usable prototypes: the entire progressive surface is measured using special measuring machines, allowing adjustment of the measured values to the mathematical data of the specified progressive surface. Not until this often difficult adjustment procedure is complete is it possible to obtain the first usable prototypes for wearing trials.
In wearing trials it is possible to test the degree of wearer tolerance for the new progressive. If the tolerance rate for the new lens is low, the design is modified and the development cycle starts from the beginning again.