Contrast Visual Acuity With Bifocal Contact Lenses

Abstract

To compare the quality of vision of a bifocal rigid gas-permeable contact lens versus a bifocal soft contact lens in subjects with presbyopia. Sixteen healthy presbyopic subjects with no ocular disease but experienced with contact lens wear were enrolled in the study. Subjects randomly wore both types of bifocal lenses for 30 minutes with a washout period of 30 minutes each in a crossover manner. The primary outcome measure was the difference in contrast visual acuity. Distance and near contrast visual acuities with the two bifocal lens types were measured in different lighting environments and at multiple contrast levels. After the measurement, subjects were asked to rate their subjective vision by using the four categories with both lens types throughout the study. At the end of the study, subjects were also asked which of the two lens types they preferred. Under photopic conditions, distance and near visual acuities decreased at the 25% and 10% contrast levels, respectively, in subjects wearing bifocal soft contact lenses (P<0.05). Under scotopic conditions, distance visual acuity decreased at the 5% contrast level with the bifocal rigid gas-permeable contact lenses (P<0.05). For subjective responses of clarity, there were no differences between lens types for distance vision (P>0.05), but bifocal rigid gas-permeable lenses were clearer than bifocal soft contact lenses for near vision (P<0.05). Bifocal rigid gas-permeable contact lenses showed better visual performance than bifocal soft contact lenses did.