Power of Bausch and Lomb Soflens™ Contact Lenses

Sarver, Morton D.; Harris, Michael G.; Mandell, Robert B.; Weissman, Barry A.

doi:10.1097/00006324-197303000-00002

Cited by 6 publications

(12 citation statements)

References 0 publications

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“…Our measurement methodology generated similar differences between observed and expected sphere power as some of the earlier studies. Figure 7 plots the difference data from two hydrogel lenses (circles, black line) of the current study and best-fit lines representing data from the previous results of Holden et al, 6 Weissman, 51 the equal percentage change hypothesis, 41 equal change hypothesis, 3 and Plainis and Charman. 5 Based on the hypothesis that the soft contact lens completely conforms to the corneal surface the optical effect of the contact lens on the eye can be determined as the difference between the optics of the eye wearing the contact lens and the eye alone 1, 2 in which case subtracting the off-eye or expected power of the contact lens from this total would yield 0.…”

Section: Discussionmentioning

confidence: 69%

“…Conformation and failure to conform are known to influence the optical effects of SCLs. Indeed, there is a long history of studies attributing unexpected refractive effects of gas permeable 1,12 and soft contact [3][4][5][6][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53] lenses to their failure to conform to the anterior corneal surface and/or lens flexure. Our measurement methodology generated similar differences between observed and expected sphere power as some of the earlier studies.…”

Section: Discussionmentioning

confidence: 99%

“…19,20 (For additional details on the derivation of the exact wet-to-in air conversion equation, see Kollbaum 2008. 11 ) The equation employed to convert wet cell to in air equivalent values for higher order aberration is a simplified version of Equation 1, and is shown in Equation 3, (3) where Z is any given Zernike term or series of terms. 11,20,21 This approximation, which assumes a lens center thickness of zero, ignores the minor effects of wavefront propagation between the two surfaces, which is appropriate given the lens thicknesses of < 0.1 mm and the low levels of higher-order aberrations typically encountered in contact lenses.…”

Section: Methodsmentioning

confidence: 99%

“…lens" between the lens and cornea, as occurs with gas permeable lens fittings. 1,3,4 Second, the lens may change shape and relative thickness while on the eye. 5 This later scenario is often termed "lens flexure", and is thought to be the primary source of under-correction by high plus powered SCLs, 5,6 with increasingly plus powered lenses losing more power (e.g.…”

mentioning

confidence: 99%

“…The term "supplemental power effect" has been used to describe this scenario, where a lens shape and/ or thickness change may occur in combination with an optically powered non-uniform thickness tear layer or "lens". 3,4 In order to confirm that some on-eye interaction effect (e.g. flexure) is responsible for the observed differences between expected and observed refractive effects of SCLs requires that the optical characteristics of SCLs be measured off-eye.…”

mentioning

confidence: 99%

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Comparing the Optical Properties of Soft Contact Lenses On and Off the Eye

Kollbaum¹,

Bradley²,

Thibos³

2013

Optometry and Vision Science

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Purpose-The purpose of the current study was to examine the on-and off-eye optical performance of two types of soft contact lenses (hydrogel and silicone hydrogel).Methods-The monochromatic aberrations (lambda = 850 nm) of contact lenses were measured on-eye using a clinical Shack-Hartmann ocular aberrometer. Additionally, we used an off-eye single-pass contact lens aberrometer (lambda = 540 nm) in which the soft contact lens was placed within a wet cell. Comparison of the lower and higher order aberrations measured with these two methods required compensation for different wavelengths and knowledge of the refractive index of the contact lens materials.Results-The measured on-eye sphere and spherical aberration values were generally similar to those measured off-eye and those specified by the lens manufacturers for both types of soft contact lenses. However, there were notable differences, especially for high plus-powered lenses, which typically exhibited lower sphere power on the eye than expected from the lens specifications and from the off-eye measured powers, both of which were almost identical. Longitudinal spherical aberration varied with lens power in the hydrogel lenses, as expected from geometrical optics theory. Longitudinal spherical aberration measurements on-and off-eye, however, deviated significantly from that expected of a thin lens with spherical surfaces due to surface asphericities. The difference between on-and off-eye optics can be modeled as a tear lens, or as relative lens thickness changes caused by lens flexure. Conclusions-The results of the current study reveal that the major difference between the oneye lens optics and the manufacturers' specifications are not due to lens errors, but due to eye-lens interactions, which could be either lens flexure or a tear lens forming behind the soft contact lens.Keywords contact lens; spherical aberration; aspheric; flexure; supplemental powerThe paraxial power of a thin lens is proportional to the difference in curvature of its front and back surfaces with a constant of proportionality equal to the difference in refractive index between the lens and surrounding material: P=(Δn)/(1/r 1 − 1/r 2 ). Likewise, a thin conforming soft contact lens (SCL) will change the refracting power of an eye by changing the curvature of the air/eye interface by the difference in curvature of its front and back surfaces. Because of this, the power of a thin SCL in air will approximate its refractive effect on the eye. 1, 2 These two values may not be identical, however, for a combination of several reasons. First, a SCL may fail to conform to the cornea creating an effective "tear Corresponding author: Pete Kollbaum, Indiana University, School of Optometry, 800 East Atwater Ave, Bloomington, IN 47405, kollbaum@indiana.edu. The authors have no financial interest in any of the products or instruments used in this study. lens" between the lens and cornea, as occurs with gas permeable lens fittings. 1,3,4 Second, the lens may change shape and relative thickness w...

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