Short communicationOptical quality of rotationally symmetrical contact lenses derived from their power profiles
Introduction
Simultaneous image contact lenses (CLs) are the most popular CLs for presbyopia compensation [1], [2]. These lenses are based on the principle of simultaneous vision [1], where two or more images are formed simultaneously at the subject’s retina. For this principle to work, the visual system must select the best focused image and supress the rest.
Currently, there is a fair amount of different simultaneous image CLs designs available in the market (e.g. center-near, center-distance designs) with different addition powers [1], [2] and different number of zones or rings; thus knowing their power distribution is essential. In the last years, several studies have evaluated the power distribution of simultaneous image CLs based on their power profiles [3], [4], [5], [6], [7]. A power profile shows how the refractive power provided by a lens varies with the radial distance. Typically, the power profiles analysed are from rotationally symmetric CLs, since in this case a single power profile represents the refractive power distribution of the whole lens. If a CL does not present rotational symmetry (e.g. toric CL, angular patterns), then one power profile is not enough to know the refractive power distribution of the whole lens.
Power profiles, when interpreted correctly, offer useful information about the work distances that simultaneous image CLs can cover and about the effect of pupil size upon the power distribution [5], [7]. However, power profiles cannot offer a thorough analysis regarding the optical quality of these lenses. For this reason, a methodology based on the vergence maps described by Nam et al. [8], [9] was proposed. This methodology allows the assessment of the optical quality of rotationally symmetrical simultaneous image CLs by calculating the lens wavefront from a sole power profile.
Section snippets
Contact lenses designs
Three simulated power profiles were considered in this study. All the power profiles corresponded to CLs that had a nominal power of 0 D and a spherical aberration of −0.075 D/mm2. A negative value of spherical aberration is typically found in some CLs. The first power profile simulated a monofocal CL, the second a two-zone center-near [1], [2] bifocal design with an addition power of 2 D, and the third a four-zone center-distance [1], [2] bifocal design, also with an addition power of 2 D. The
Results
The VSOTF values for each design, with respect to the vergence and the pupil diameter can be seen in Fig. 2. The white solid curves demarcate the zones where the VSOTF was equal or greater than 0.12. The upper panel corresponds to the VSOTF values obtained for the monofocal design, which presents only optimal VSOTF values at one vergence or working distance, in this case far. The peak got displaced to the right as the pupil diameter increased as a consequence of the negative spherical
Discussion
A methodology that allows for a rapid and thorough assessment of the optical quality of rotationally symmetrical CLs, based just on a power profile, has been presented. It can be particularly useful in optical quality evaluation of simultaneous image CLs [1], [2] since the effect of the pupil size on these elements is paramount [21]. This methodology presents a series of advantages with regards to the direct evaluation of power profiles, since further information, other than power distribution,
Financial disclosure
The authors have no proprietary interest in any of the products or devices mentioned in this article.
Acknowledgements
This work was supported by the University of Valencia (Atracció de talent program) [UV-INV-PREDOC14-179135]; the Ministerio de Educación, Cultura y Deporte [FPU13/05332], and the Marie Curie Initial Training Network [FP7-PEOPLE-2013-ITN] AGEYE project [608049], granted by the European Commission, Brussels, Belgium, [608049];
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