Visual performance in the correction of astigmatism with contact lenses: Spherical RGPs versus tonic hydrogels

Abstract

The purpose of this study was to evaluate visual performance with both spherical rigid gas permeable (RGP) and tonic hydrogel contact lenses. We hypothesized that both visual acuity and performance would be inferior with hydrogel lenses because of dynamic crossed-cylinder effects with eye movement-induced lens rotation. Eighteen subjects (23–45 years) having 0.75–2.50 D of astigmatism in each eye and matching corneal toricity were fitted with both types of lenses (providing at least 20 20 Snellen VA). Seventeen subjects successfully wore each lens type on a full-time basis for 3 weeks prior to testing. Our randomized, crossover study included logMAR threshold visual acuity, contrast sensitivity, and a VDT text-editing task interrupted by a short reading task in upper lateral gaze. Visual performance was assessed by counting errors identified, the error detection rate, and the total number of lines edited. Subjects rated the comfort, quality, and stability of vision just before and after the VDT text-editing task. Subjective ratings were also obtained at the end of the overall wearing period of each lens type in regard to lenswear comfort, visual clarity, and visual stability. Patients chose which pair of lenses to keep after the study. Our analysis of these data indicated no significant differences between threshold visual acuity or pre-post VDT task-related ratings of visual comfort, quality, or stability between the two types of lenses. Contrast sensitivity results were also not different between lens types. The overall ratings at the end of the wearing weeks of each type of lens indicated that tonic hydrogels were better than were RGP lenses for wearing comfort, dryness, and handling, whereas the RGP lenses were rated better for clarity of vision. Stability of vision was rated the same between the two lens types. Seventy-four percent of the subjects chose to continue wearing the tonic hydrogels after the study, whereas 24% chose the RGP lenses. These results suggest that tonic hydrogels can provide equivalent visual performance to spherical RGP contact lenses. Although overall clarity of vision was rated as better with RGP lenses by the subjects, there was a strong final preference for hydrogel lenses, largely due to better overall lens wearing comfort.