The effect of pupil size on visual performance with center-distance soft multifocal contact lenses

Multifocal contact lenses have been shown to slow myopia progression in children. Understanding their impact on visual performance is important. While these lenses have little effect on high-contrast visual acuity, they reduce low-contrast visual acuity and contrast sensitivity, with these reductions being greater as pupil size increases.

This study aimed to determine the effect of pupil size on visual performance with center-distance multifocal contact lenses used for myopia control.

Twenty-four myopic, nonpresbyopic adults were fitted with a single vision (Biofinity) and a center-distance multifocal (Biofinity D +2.50 add) contact lens, in random order. The pupil was dilated, and visual acuity (high and low contrast) and contrast sensitivity were measured through a 3 and 6 mm aperture.

Visual acuity differed by contrast level and depended on lens design and pupil size (p=0.0040). With both pupil sizes, high-contrast acuity with the multifocal lens was only two letters worse than with the single vision lens (p=0.0001). Lens design effects on low-contrast acuity were pupil size-dependent (p=0.0006). Compared with single vision lenses, low-contrast acuity with multifocal lenses was about three letters worse for a 3 mm pupil (mean ± standard error of the mean = 0.07 ± 0.02 logMAR, p=0.0010) and about two lines worse with a 6 mm pupil (0.19 ± 0.02 logMAR; p<0.001). While wearing the multifocal lens, low-contrast acuity decreased by nearly two lines when pupil size increased from 3 to 6 mm (0.17 ± 0.02 logMAR; p<0.0001). The effect of lens design on the area under the log contrast sensitivity function was pupil-size-dependent (p=0.024). When compared with a 3 mm pupil, the greatest reduction in area under the log contrast sensitivity function at the larger 6 mm pupil size was with the multifocal lens, causing a 17% decrease compared with a 9% decrease for the single vision lens (p<0.0001).

Multifocal contact lenses perform similarly to single vision lenses under high-contrast and smaller pupil conditions; however, visual performance reductions increase with lower contrast and a larger pupil size.