Purchase this article with an account.
J. Tarrant, C. F. Wildsoet; Interactions Between the Zernike Modes, Spherical Aberration and Defocus, During Accommodation and Effects of Multifocal Soft Contact Lenses. Invest. Ophthalmol. Vis. Sci. 2007;48(13):1510. doi: https://doi.org/.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Previous studies have shown that the Zernike modes, defocus and spherical aberration, interact constructively to enhance retinal image quality. The purpose of this study was to assess the effect on the Zernike defocus mode of adding positive spherical aberration (SA) using multifocal soft contact lenses (MF) during accommodation.
Aberration data were collected from 30 subjects (13 emmetropes and 17 myopes) for each of 6 different target vergence settings, 0, 1.5, 2, 3, 4 and 5 D, and 3 different soft contact lenses, single vision distance lenses (SVD) and 2 multifocal contact lenses (MF15D; +1.50D add and MF2D; +2.00D add). The MF lens design included a center distance prescription zone of 2.3 mm diameter, surrounded by a 5 mm wide zone of progressively increasing power to the full reading addition. A Wavefront Sciences COAS instrument was used in these measurements. Linear regression analyses were used to assess the relationship between the Zernike modes, defocus and SA across the target vergence range, for each lens type and refractive group.
For all vergence setting, all eyes showed relative increases in positive SA with the MF lenses in place, as predicted from their design. This trend was significant (p < 0.017) for all vergence settings and both MF lenses compared to the SVD lens for emmetropes, and for myopes for 3 of the 6 vergence settings for the MF15D lens and all vergence settings for the MF2D lens. Myopes also had significantly lower amounts of SA (p < 0.05) at all vergence-lens combinations compared to emmetropes except with the MF2D lens and the 5 D vergence setting. For emmetropes, the lens-induced increase in positive SA appeared to stimulate accommodation; there was an increase in Zernike defocus and a consistent trend of decreasing pupil diameter from the SVD to the MF15D to the MF2D lens, for each vergence demand over the 0 to 3 D range. This effect was not apparent with either of the MF lenses for myopes over this vergence range. For higher (4 and 5 D) vergence settings, Zernike defocus increased as pupil diameter decreased with the MF15D lens, and decreased as pupil diameter increased with the MF2D lens, for both groups.
Observed increases in Zernike defocus in combination with decreases in pupil diameter imply increases in accommodation resulting from lens-induced increases in positive SA. That such responses were seen in emmetropes at all vergences and for myopes at higher vergence levels, suggests that Zernike defocus and SA interact during accommodation, and that the magnitude of the accommodative response can be manipulated by altering SA.
This PDF is available to Subscribers Only