Influence of the base curve in the performance of customized and classical progressive lenses.

PURPOSE

The aim of this article is to analyze the effect of the base curve on progressive power lens performance by means of the Sheedy scoring technique. We expect to find strong differences on this effect depending on the definition of lens power and on the lens optimization method.

METHODS

We have used six different back side progressive lens designs. Three of them have been optimized for improving the power perceived by the user in the actual position of use. The other three have been optimized to provide prescription power when measured with a focimeter or a mapper. We have used exact ray tracing to compute both the user power maps and the focimeter power maps. We have applied the Sheedy method to these maps and analyzed the results.

RESULTS

When this scoring technique is run with focimeter power maps, the performance of customized lenses is highly base curve dependent. Instead, classical lens performance is quite stable against base curve changes. On the contrary, if we run the test with user power maps, we find the opposite behavior.

CONCLUSIONS

Progressive lens scoring is highly dependent on how the lens has been designed and how the lens is measured. Besides, customization of progressive lenses by real ray tracing guarantees that prescription and design parameters are preserved at the position of use regardless the base curve selected to make the lens.