Lens Design Techniques to Improve Satisfaction in Free-Form Progressive Addition Lens Users

Abstract

Purpose: The goal of this study is to analyze the impact of different techniques for designing Free-Form progressive addition lenses in the overall satisfaction of users. Personalization of Free-Form lenses according to personalization parameters, variations in the characteristics of the base curve and differences in mean power in the lateral areas of the progressive lens were analyzed. Material and Methods: A comparative study comprised of 3 phases was done to determine differences between 3 pairs of Free-Form progressive lenses: Lens 1A-Basic (non-personalized) & Lens 1B-DRP (personalized), Lens 2A-Spherical (spherical base curve) & Lens 2B-Camber (variable base curve) and Lens 3A-Standard (positive mean power in lateral areas) & Lens 3B-Steady (null mean power in lateral areas). In each phase, a theoretical analysis was carried out of the power distribution maps of the progressive addition lenses based on a model of the lens-eye system to calculating the exact ray tracing for the real positions of wear. Also, a double-blind wearer trial was done in which a group of subjects tested each design for 7 days and rated their general comfort and preference while performing their daily activities. Results: Theoretical analysis for lenses 1A-Basic and Lens 1B-DRP showed some differences in the values of unwanted astigmatism in the lateral areas of the lenses. When subjects compared the lenses, a clear preference for Lens 1B-DRP was observed: 63% of the users selected the lens 1B-DRP compared to 20% who selected Lens 1A-Basic (p=0.0001). For lenses 2A-Spherical and lenses 2B-Camber, power distribution maps showed identical power distribution maps. However, subjects significantly preferred lens 2B-Camber: 62% preferred the lens 2B-Camber against the 33% who selected the lens 2A-Spherical (p=0.03). Lenses 3A-Standard and 3B-Steady presented similar Sheedy contours for spherical and cylindrical power but vary in mean power in the lateral areas of the lens. Wearer trial results showed that 53% of users preferred Lenses 3B-Steady against 33% of user who preferred Lenses 3A-Standard. Conclusions: Personalization of Free-Form lenses according to personalization parameters, the use of a variable base curve that increases in curvature from the top to the bottom of the lens and control of mean power in the lateral areas of the progressive lens are good and valid techniques to improve general satisfaction of Free-Form progressive addition lenses users.