Mapping And Measuring Differences Between Free-Form Progressive Lenses.

Background: This experimental study aims to test the repeatability of the fabrication of
identical free form progressive lens orders between five optical laboratories.
Methods: Five identical orders of free form progressive lenses were placed to five separate optical laboratories. The right and left lenses of each order were then mapped by the Rotlex Class Plus lens analyzer. The Class Plus supervisor mode software was then used to create a comparison map between all right and left lenses to one another. Results: Small differences were found between sphere and cylinder power measurements from comparison maps. The largest variance in measurements was found in comparing addition power between lenses. These values had the highest standard deviation and variance.
Conclusion: Possible explanations for larger inconsistencies in addition power
measurement include incorrect identification of near zone power secondary to user
misalignment during measurement, and environmental or mechanical differences in lens production between optical laboratories. A small contribution of inaccuracy may be
attributed to variation in base curve and central thickness measurement.