Abstract
Purpose :
Although bifocal soft contact lenses (SCLs) have been found to be effective in managing myopia progression, its mechanism remains unclear. This study aims to characterize through-focus peripheral optical quality with a bifocal SCL and to test the hypothesis that optical blur orientation through-focus, across the visual field, has a potential role in myopia control.
Methods :
A custom-built wide-field scanning wavefront sensor was used to measure the right eye’s aberrations in five young adults with myopia (-2.75±1.26D) wearing monofocal (Acuvue Oasys) and +2.5D ADD bifocal SCLs (Acuvue Oasys for Presbyopia, Johnson & Johnson). The measurement was taken across retinal eccentricities ranging ±30° horizontal, ±15° vertical and ±20° oblique meridians. Through-focus point spread functions (PSFs) for -4D to 4D were computed from the measured aberrations. Blur orientation along radial and azimuthal directions were estimated from the PSFs using vector analysis. The slope of blur orientation change through-focus was also evaluated.
Results :
The bifocal SCL introduced a mean myopic shift of 1.32D, compared with the monofocal SCL, across the horizontal meridian. In the nasal peripheral field, vertical astigmatism was significantly reduced by the bifocal SCL (e.g. bifocal 0.39 vs mono 0.97µm at 25°) while horizontal coma was increased (e.g. bifocal 0.62 vs mono 0.02µm at 25°). Spherical aberration was negatively shifted (-0.11±0.08µm) by the bifocal SCL across the horizontal meridian. Overall, root-mean-square of higher-order aberrations with the bifocal SCL was 1.4 times higher than the monofocal SCL at 0°. This difference was increased up to 2.2 times at 30°. The through-focus image quality with the bifocal SCL showed increased depth of focus (DoF) compared with the monofocal SCL. The bifocal SCL reduced the slope of through-focus change in blur orientation significantly at 20 to 30° by 14 to 33%. Three other meridians showed similar but less significant trends.
Conclusions :
Bifocal SCLs introduce a significant increase in DoF and a decrease in the blur orientation anisotropy in the peripheral visual field. Supported by the peripheral neural anisotropy found in our previous study (Zheleznyak et al., 2016), we propose that peripheral blur orientation provides a cue for eye growth, and that a reduction in the blur orientation anisotropy is a mechanism underlying the therpeutic effect of bifocal/multifocal SCLs in myopia control.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.