Visual acuity with spherical and toric soft contact lenses in low- to moderate-astigmatic eyes

Purpose. To evaluate the visual acuity of myopic, astigmatic eyes, with spherical and toric soft contact lenses. Methods. A randomized, masked, cross-over study was conducted to compare acuity with soft spherical and toric contact lenses on patients with between -0.75 and -2.00 D of refractive astigmatism. A total of 15 patients (30 eyes) were fitted with four brands of spherical and toric lenses (Acuvue Advance, Biomedics 55, Frequency 55, and SofLens 66), in random order. An initial visit was conducted to fit the lenses and an over-refraction (OR) was performed to determine the best prescription. At the measurement visit, patients' pupils were dilated with 1.0% tropicamide and 2.5% phenylephrine to allow wavefront aberration measurements, and a final OR was performed. A 6-mm aperture was held in front of the eye to measure visual acuity through just the contact lens and the contact lens with the final OR. Acuity was measured monocularly, under photopic and mesopic conditions with high- and low-contrast logMAR charts at distance. Differences in acuity were analyzed using repeated measures analysis of variance. Results. Visual acuity with soft spherical contact lenses was not significantly different between lens brands. For toric contact lenses, acuity was significantly better with Biomedics 55 and SofLens 66 than with Acuvue Advance; and acuity with SofLens 66 was significantly better than with Frequency 55. Low-astigmatic eyes gained between 3 and 5.5 letters of acuity with toric contact lenses vs. spherical lenses; and moderate-astigmatic eyes gained between 8 and 12.5 letters. Conclusions. Both low- and moderate-astigmatic eyes showed improvements in acuity with toric contact lenses. Lens brand had a measurable effect on acuity for toric contact lenses. Further investigation of aberrations induced by contact lens design is warranted to explain the observed differences in visual performance.