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

Doll, Tamsin, Moore, Joshua ORCID: 0000-0003-2233-2527, Shihab, Ahmad H, Lopes, Bernardo T, Eliasy, Ashkan ORCID: 0000-0002-4473-1900, Maklad, Osama ORCID: 0000-0001-6893-2654, Wu, Richard, White, Lynn, Jones, Steve ORCID: 0000-0002-8977-8403, Elsheikh, Ahmed ORCID: 0000-0001-7456-1749
et al (show 1 more authors) (2020) Which feature influences on-eye power change of soft toric contact lenses: Design or corneal shape? PLOS ONE, 15 (11). e0242243-.

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<h4>Purpose</h4>This study investigates how both the peripheral zone design and corneal shape affect the behaviour of soft contact lenses on-eye.<h4>Methods</h4>In this study, soft contact lenses of varying nominal cylindrical powers and peripheral zone designs-a single-prism gravity-based stabilised lens (G1P), two-prism blink-based stabilised lens (B2P) and four-prism blink-based stabilised lens (B4P)-were generated as finite element models. The on-eye simulation results were analysed to identify the impact of each peripheral zone design (Each with different volume ratios) on the effective power change (EPC) when worn by a subject. Topographies of three eyes of varying average simulated anterior corneal curvature (flat, average & steep) were used in this study.<h4>Results</h4>The volume of the lens's peripheral zone as a ratio of the total lens volume (Vp) recorded very weak correlations with the effective power change (EPC) among the three investigated designs when they were fitted to the flat eye (R = -0.19, -0.15 & -0.22 respectively), moderate correlations with the average eye (R = 0.42, 0.43 & 0.43 respectively) and strong correlations with the steep eye (R = 0.91, 0.9 & 0.9 respectively). No significant differences were noticed among the three investigated designs and none of the cylindrical lenses designed with axis 90° recorded EPC values outside the acceptance criteria range (ACR) of ±0.25 D. No significant differences in EPC were recorded among the three designs G1P, B2P and B4P (p>0.6) when they were designed with three axes at 90°, 45° and 0°. Moving the toric lens axis away from 90° dragged the EPC to the negative side and most of the investigated lenses with axes at 45° and 0° recorded EPCs outside the ±0.25D range.<h4>Conclusions</h4>In all cases, the shape of the cornea had a more dominant effect on EPC when compared to the peripheral zone design. Corneal shape influences the soft toric contact lens's on-eye power change more than the lens design.

Item Type: Article
Uncontrolled Keywords: Cornea, Humans, Corneal Topography, Equipment Design, Contact Lenses, Hydrophilic, Finite Element Analysis, Adult, Female, Male, Young Adult
Depositing User: Symplectic Admin
Date Deposited: 02 Nov 2020 09:10
Last Modified: 03 Feb 2023 13:08
DOI: 10.1371/journal.pone.0242243
Related URLs:
URI: https://livrepository.liverpool.ac.uk/id/eprint/3105741