Page 63 - Demo

and a relatively high price meant that they never took off in the market. Spherical and aspheric lenses have become a commodity product with little performance distinction among different brands. As a result, the main competitive differentiation has become price; today these lenses are low cost and offer relatively low pro ts for eyecare practices compared to progressive lenses. With virtually no technological breakthroughs to talk about, they more or less became an invisible product.
ENTER FREEFORM MANUFACTURING
The advent of freeform manufacturing for eyeglass lenses opened up new possibilities, revolutionizing single vision lenses just as it has done for progressive lenses.
To understand the difference that freeform manufacturing has made, we need to brie y look at the traditional approach to manufacturing lenses. Traditional single vision lenses are manufactured in one of two ways: Finished, meaning that the lens design and the prescription power were molded into the lens by the manufacturer; and semi- nished, where the lens design (front surface) was molded by the manufacturer, and the prescription was applied to the back surface by the lab, using symmetrical spherical and cylindrical tools. These manufacturing approaches still account for the great majority of single vision lenses.
Freeform manufacturing is a far more exible manufacturing process. In freeform, a computer- driven, single-point diamond cutting tool is used to apply both the design and the prescription to a
spinning plastic “puck” with a front curve only. A freeform generator can apply virtually any curve, no matter how complex, to a puck, allowing it to be free of the restrictions of traditional surfacing.
FREEFORM CUSTOMIZATION
Freeform shifts the main part of the manufacturing effort from the factory to the freeform-enabled lab, where the lens can essentially be created in real-time, after the lens has been ordered. Therein lies the key to the bene ts of freeform: If the lens can be manufactured after the ECP has placed the order (effectively in real-time), the design can also be modi ed based on information speci c to the individual patient. That means that a unique customized lens can be designed and manufactured for the needs of each wearer.
Why does that matter? It’s easy to assume that because there has been so little evolution, traditional single vision lenses must offer the best visual experience possible. However, single vision lenses have suffered from inconsistent performance and visual limitations that are in some ways similar to those experienced with traditional progressives. One limitation comes from the use of standard base curves. Readers familiar with Tscherning’s Ellipse will recall that there is an ideal base curve for every sphere power. However, the limitations of the traditional manufacturing, distribution and inventoryprocessmeantthatonlyafewbasecurves had to cover the entire range of sphere powers. Patients with prescriptions that corresponded closely to a base curve would enjoy the best vision,
63 EYEZONE Issue 91-92 May / August 2020