Theoretical fitting characteristics of typical soft contact lens designs

Sulley, Anna; Lorenz, Kathrine Osborn; Wolffsohn, James S.; Young, Graeme P.

doi:10.1016/j.clae.2017.04.001

Cited by 8 publications

(6 citation statements)

References 17 publications

(25 reference statements)

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“…Kollbaum [9] has suggested that further investigation of supplemental power change may be essential to achieve predictable and optimised lens design performance. This corroborates well with the recent work of Sulley et al demonstrating the wide variation in theoretical fitting success rates of soft contact lenses (61% - 90%) despite a narrow range of parameters varying between commercial designs (Base curve radius 8.4 mm to 9.0 mm, and D from 13.8 mm to 14.3 mm) [10]. Historically, changes to optical power from corneal conformance have been estimated roughly.…”

Section: Introductionsupporting

confidence: 88%

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Simulated optical performance of soft contact lenses on the eye

et al. 2019

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Purpose To evaluate the impact of soft contact lens eye-fit on optical power by computational modelling and to produce correction maps for reversing this impact during the design process. Methods Finite element models of spherical and toric hydrogel contact lenses at varying nominal powers of -20 D to +20 D, base curves radii (R 1b ) of 8.2, 8.5, 8.8 mm, and overall diameters (d 3 ) of 14.5, 15.0, 15.5 mm were generated. Lenses were fitted to computational eye models generated with human eyes’ topography data. Combined eye-lens simulations were run under the boundary conditions of the tears’ surface tension between the contact lens and the eye in addition to the eyelid blink pressure. Lens optical zone power changes were calculated through computational light-ray tracing methods following each simulation. Results Effective power changes (EPC) were affected negatively for all toric simulated lenses with power varying from -20 D to +20 D. Spherical lenses demonstrated similar behaviour, however with some positive EPC over the power range from -20 D to -10 D for spherical power (SPH) lenses. EPC assessment was between +0.25 D and -0.5 D for most lenses, however, lenses with prescriptions from +10 D to +20 D incurred EPC outside this range. The spherical lenses showed a maximum effective power change of +1.046 ± 0.338 D (Average Eye), and a minimum of -3.278 ± 0.731 D (Steep Eye). Similarly, the toric lenses showed a maximum of +1.501 ± 0.338 D (Average Eye), and a minimum of -3.514 ± 0.731 D (Steep Eye). EPC trends, along with minimum and maximum power, generally increased negatively as nominal lens prescription increased positively. Contact lens base curve selection affected the assessed effective power change for both spherical and toric lenses. The effect from lens total diameter for spherical lenses was less substantial than that for toric lenses. Conclusions This study considered the impact of soft contact lens design parameters on effective optical power changes (EPC) after eye-fit. Spherical lenses experienced more EPC of clinical significance (>0.25 D) than toric lenses. Both types of lenses, spherical and toric (simple astigmatism), demonstrated similar trends in EPC on fitting from -20 D to +20 D, with lenses in the extremely positive and the extremely negative prescriptions demonstrating the highest EPCs. The lens base curve impacted the extent of EPC observed, with flatter base curves experiencing less power change. Diameter proved to impact toric lenses more than spherical ones, however generally the diameter has less effect on power change than base curve selection.

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Section: Introductionsupporting

confidence: 88%

“…al. [10], it was identified that the biggest opportunity for achieving a soft contact lens fitting success was to increase the lens diameter, hence improving corneal coverage. Lenses tested in Sulley et.…”

Section: Methodsmentioning

confidence: 99%

Simulated optical performance of soft contact lenses on the eye

et al. 2019

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“…More recently, an ellipto-conical corneal modelling of soft lens fit showed closer concordance with actual measurements than an elliptical model and estimated an edge strain of 2.7% for a standard 8.6 mm base curve, 14.2 mm diameter lens on an average eye, with edge strain <0% being too loose and >6% being too tight [326,349]. This modelling showed that theoretical success rates for one base curve would be 61-90% with not much improvement from a second base curve [350]. Increasing lens diameter to >2 mm more than the HVID does not negatively impact the eye if the base curve is adjusted to keep the sag the same [327].…”

Section: Modelling Of Lens Movementmentioning

confidence: 53%

BCLA CLEAR - Evidence-based contact lens practice

Wolffsohn

Dumbleton

Huntjens

et al. 2021

Contact Lens and Anterior Eye

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“…In soft contact lens design, the peripheral zone is a specific region connecting the optic zone to the edge profile. This zone is substantial in contact lens fitting; it has been shown that the peripheral corneal shape has a more significant role in successful contact lens wear than the central radius of curvature of the cornea [3,4]. Also when a soft contact lens is fitted to a cornea, it is the peripheral zone that flexes and deforms most [5] which may then influence the optic zone, to which it is connected.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2020

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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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Theoretical fitting characteristics of typical soft contact lens designs

Abstract: Mathematical modelling is a useful method for testing SCL design combinations. The results suggest that judicious choice of additional fittings can expand the range of fitting success.

Cited by 8 publications

References 17 publications

Simulated optical performance of soft contact lenses on the eye

Simulated optical performance of soft contact lenses on the eye

BCLA CLEAR - Evidence-based contact lens practice

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

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