1 First ideas, first patents
The first patent of a progressive lens was granted to Owen Aves in 1907 (UK 15 735). In this invention the progressive power was the result of the combined effect of a progressive cylindrical front surface with horizontal axis and a conical back surface apex downwards. There were other proposals creating the progression with both surfaces, a concept which had the advantage to use surfaces of revolution easier to manufacture, but the inconvenience that at that time it was difficult to incorporate the prescription in the second surface contributing to the progression.
The history of the beginning of the progressive lenses is analyzed in detail in several publications for example by Sullivan and Fowler , and Maitenaz .
To preserve the second surface exclusively for the correction of the ametropia means to realize the power increase from far vision to near vision on only one surface. Usually the line of the surface corresponding to the path of the converging eye for central vision is called the principal meridian. According to the laws of differential geometry, it is only on the principal meridian where the progression power can be spherical (umbilical line). To both sides of this meridian there is surface astigmatism increasing to the edge of the surface (Minkwitz theorem).
In a remarkable patent (US 1 143 316, application 1911) the French inventors Georges Poullain and Julien Cornet present different progressive lens concepts including a design with an umbilical main meridian, circles as orthogonal sections and stabilized far and near vision zones. In other examples a power increase at the bottom of the lens enables the wearer to see the ground at his feet and also where each of the two surfaces has a progressive main meridian. But there is no discussion of the lateral optical quality and little about the manufacturing process. The patent says about the process of manufacturing:
“In order to obtain the surfaces indicated above, the methods ordinarily employed by opticians for cutting spherical, cylindrical or toric lenses would not be suitable and that it would be necessary to have recourse to special machines”