Simulation of the Effect of Material Properties on Soft Contact Lens On-Eye Power

Abstract

Purpose: To evaluate the variation in the optical power achieved following soft contact lens eye fitting for spherical and cylindrical lenses with differing hydrogel material properties. Methods: Uniaxial tensile tests were performed on four hydrogel materials 77% water-content (w-c) hydrogel, 74% w-c blue silicone hydrogel, 74% w-c clear silicone hydrogel, and 64% w-c clear hydrogel (shortly referred to as H77p0, SiH74p5-blue, SiH74p5-clear, and H64p0-clear), under loading conditions that would be expected in vivo. Finite element models of the cornea and contact lens interaction were generated using spherical and cylindrical lenses with powers varying from −10 to +20 D; overall diameters of either 13.5, 14.0, or 14.5 mm; and with material properties matching those determined through experimental testing. Results: The moduli of elasticity for each of the tested hydrogel materials were 0.195 ± 0.027 MPa, 0.277 ± 0.019 MPa, 0.279 ± 0.01 MPa, and 0.457 ± 0.013 MPa for H77p0, SiH74p5-blue, SiH74p5-clear, and H64p0 respectively. The calculated values of effective power change (EPC) showed strong negative correlations with lens power. This was particularly apparent in the higher end of the lens power spectrum (over +5 D), where each of the materials demonstrated a highly linear reduction in EPC with increased lens power. Conclusions: Soft contact lenses composed of a stiffer hydrogel are far more resilient to changes in EPC across the lower end of the lens power spectrum (−10 to +5 D). Beyond this range, the material choice does not have a significant effect on the EPC.

Which feature influences on-eye power change of soft toric contact lenses: Design or corneal shape?

“…This study investigates the effect of employing three different peripheral zone stabilisation designs on the EPC then determines which feature influences on-eye EPC, the eye shape or the contact lens design. Although the authors' previous studies have been conducted on the effect of contact lens power on EPC [5,30], this work introduces a new and more relevant approach, where the eye is not considered as a rigid solid body. In terms of design, the lenses considered in this study are designed using three peripheral zone designs, whereas the previous studies [5,30] only considered a single peripheral zone.…”

“…Although the authors' previous studies have been conducted on the effect of contact lens power on EPC [5,30], this work introduces a new and more relevant approach, where the eye is not considered as a rigid solid body. In terms of design, the lenses considered in this study are designed using three peripheral zone designs, whereas the previous studies [5,30] only considered a single peripheral zone. Previous studies [5,30] employed lenses that, https://doi.org/10.1371/journal.pone.0242243.g002…”

“…In terms of design, the lenses considered in this study are designed using three peripheral zone designs, whereas the previous studies [5,30] only considered a single peripheral zone. Previous studies [5,30] employed lenses that, https://doi.org/10.1371/journal.pone.0242243.g002…”

“…A custom-built MATLAB script was written to generate the geometrical shape of the lenses based on the type of balance zone design, the design parameters and the optical power values. Although the design process has been covered in previous studies [5,30], for completeness, details of the lens design are presented in Appendix B. In addition to the details dealt with in previous work, the fillet design and new peripheral zone design techniques are also outlined (see S1 File).…”

Finite Element Analysis of Cornea and Lid Wiper During Blink, With and Without Contact Lens

“…Different soft CL geometries have been explored, in the previous research [64][65][66] . Complete speci cs of the exact contact lens geometries were not available in the literature.…”