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Doll T, Moore J, Shihab AH, Lopes BT, Eliasy A, Maklad O, Wu R, White L, Jones S, Elsheikh A, Abass A. Which feature influences on-eye power change of soft toric contact lenses: Design or corneal shape? PLoS One 2020; 15:e0242243. [PMID: 33237951 PMCID: PMC7688134 DOI: 10.1371/journal.pone.0242243] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2020] [Accepted: 10/30/2020] [Indexed: 12/25/2022] Open
Abstract
PURPOSE This study investigates how both the peripheral zone design and corneal shape affect the behaviour of soft contact lenses on-eye. METHODS 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. RESULTS 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. CONCLUSIONS 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.
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Affiliation(s)
- Tamsin Doll
- School of Engineering, University of Liverpool, Liverpool, United Kingdom
| | - Joshua Moore
- School of Engineering, University of Liverpool, Liverpool, United Kingdom
- Department of Mathematical Sciences, University of Liverpool, Liverpool, United Kingdom
| | - Ahmad H. Shihab
- School of Engineering, University of Liverpool, Liverpool, United Kingdom
- School of Engineering, University of Hertfordshire, Hatfield, United Kingdom
| | - Bernardo T. Lopes
- School of Engineering, University of Liverpool, Liverpool, United Kingdom
- Department of Ophthalmology, Federal University of Sao Paulo, Sao Paulo, Brazil
| | - Ashkan Eliasy
- School of Engineering, University of Liverpool, Liverpool, United Kingdom
| | - Osama Maklad
- School of Engineering, University of Liverpool, Liverpool, United Kingdom
| | - Richard Wu
- Department of Optometry, Central Taiwan University of Science and Technology, Taichung, Taiwan
- College of Optometry, Pacific University, Forest Grove, Oregon, United States of America
| | - Lynn White
- Ultravision CLPL, Leighton Buzzard, United Kingdom
| | - Steve Jones
- School of Engineering, University of Liverpool, Liverpool, United Kingdom
| | - Ahmed Elsheikh
- School of Engineering, University of Liverpool, Liverpool, United Kingdom
- School of Biological Science and Biomedical Engineering, Beihang University, Beijing, China
- National Institute for Health Research (NIHR) Biomedical Research Centre at Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, London, United Kingdom
| | - Ahmed Abass
- School of Engineering, University of Liverpool, Liverpool, United Kingdom
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