Clinical research
Progressive addition lenses—measurements and ratings

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Abstract

Background

This study is a followup to a previous study in which the optics of several progressive addition lens (PALs) designs were measured and analyzed. The objective was to provide information about various PAL designs to enable eye care practitioners to select designs based on the particular viewing requirements of the patient.

Methods

The optical properties of 12 lenses of the same power for each of 23 different PAL designs were measured with a Rotlex Class Plus lens analyzer. Lenses were ordered through optical laboratories and specified to be plano with a +2.00 diopters add. Measurements were normalized to plano at the manufacturer-assigned location for the distance power to eliminate laboratory tolerance errors. The magnitude of unwanted astigmatism and the widths and areas of the distance, intermediate, and near viewing zones were calculated from the measured data according to the same criteria used in a previous study.

Results

The optical characteristics of the different PAL designs were significantly different from one another. The differences were significant in terms of the sizes and widths of the viewing zones, the amount of unwanted astigmatism, and the minimum fitting height. Ratings of the distance, intermediate, and near viewing areas were calculated for each PAL design based on the widths and sizes of those zones. Ratings for unwanted astigmatism and recommended minimum fitting heights were also determined. Ratings based on combinations of viewing zone ratings are also reported.

Conclusions

The ratings are intended to be used to select a PAL design that matches the particular visual needs of the patient and to evaluate the success and performance of currently worn PALs. Reasoning and task analyses suggest that these differences can be used to select a PAL design to meet the individual visual needs of the patient; clinical trials studies are required to test this hypothesis.

Section snippets

Measurement method

The lens measurement method was identical to that previously reported.3 All lenses were measured using the Rotlex Class Plus lens analyzer to provide sphere, cylinder, and axis values across the surface of the lens. The lenses were measured by aligning the prism reference line markings appropriately in the instrument. All of the measurements were made using the Rotlex “DST” mode; hence, all measurements were normalized to an assigned power of plano at the location recommended by the

Results

The criteria for measuring and reporting the zone width, zone area, astigmatism measurements, and ratings are identical to those used in the previous study.3 The rationale for selecting the particular criteria are reported in the previous publication and are not repeated here. Likewise, the validity of the measured widths and areas insofar as they are related to the performance of everyday tasks was discussed in the previous publication and is not presented here.

Discussion

The measurements and analyses of the PALs in this study are performed with the goal of providing clinicians with information that will assist them in providing appropriate treatment options for their patients. There are tradeoffs in the design of a PAL5; therefore, no single design can be optimized for all characteristics. The measurements in this study show that the balance of tradeoffs can vary widely for the various PAL designs in the market. Previous analyses of common visual tasks show

Conclusions

The optical characteristics of the different PAL designs are significantly different from one another. The differences are significant in terms of the sizes and widths of the viewing zones, the amount of unwanted astigmatism, and the minimum fitting height. Reasoning and task analyses3 suggest that these differences can be used to select a PAL design that matches the particular visual needs of the patient; clinical trials studies are required to test this hypothesis.

Acknowledgment

This research is supported by the Center for Ophthalmic Optics Research, a research consortium at Ohio State University. All ophthalmic companies are eligible and invited to join the consortium. The authors do not have any personal, financial, ownership, or consulting relationships with any of the companies in this study.

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