Abstract
The progressive addition lens (PAL) is a spectacle lens design with progressive refractive power changes across the lens surface to provide sharp vision at different viewing distances for patients with reduced accommodative strength. It has gained in popularity not just for presbyopic patients, but also patients with occupational (office, driving, or digital device) and therapeutic (e.g., myopia control) needs. However, despite the increasing prevalence of astigmatism in adults > 40 years old who rely on PAL correction, no metric is available to reflect the optical variation in PALs with astigmatic prescriptions. Based on recent studies, four novel optical metrics sensitive to variation of refractive power across the lens surface of PALs have been developed. These metrics were used to compare the optical performance of PALs of various prescriptions, designs, and manufacturers. For each lens, the refractive power profile was first measured with a Moire-deflectometry-based instrument.The data was then exported and analyzed using a two-dimensional error map for each of the four metrics. The results revealed significant impacts of astigmatic prescription, providing evidence for the usefulness of these metrics in quantifying the optical performance of PALs for patients with astigmatic prescriptions.
Highlights
progressive addition lens (PAL) are designed to provide continuous, additional converging powers for eyes that need extra refractive powers to see things sharply at different viewing distances
The results indicate that metrics sensitive to astigmatic prescription can quantitatively differentiate the optical performance of PALs
The four optical metrics developed in this study revealed the impacts of prescription and manufacturer on the optical performance of PALs (Tables 2 and 3)
Summary
PALs are designed to provide continuous, additional converging powers for eyes that need extra refractive powers to see things sharply at different viewing distances. The integration of multiple lens curvatures to provide additional powers in PAL inevitably induces unwanted optical blurs, the lower region at both sides of PAL being distorted by varying amounts of astigmatic blur[2] Such optical blurs degrade patient’s foveal and peripheral vision when the eye looks towards the peripheral area of the lens. Given the complex spatial distribution of aberrations across the lens surface of PAL, a comprehensive assessment of optical quality would require a global metric that can reflect the optical quality of the whole lens surface area In this respect, S heedy[17,18] proposed to evaluate the power distribution of PALs by estimating the width of clear “zones” designated for distance, intermediate, and near vision, based on the departure from the target prescription.
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