Tolerance to spherical aberration induced by rigid contact lenses

We have investigated the effects of spherical aberration (SA) on visual performance by fitting subjects with rigid lenses of varying front surface asphericity. Three pairs of lenses were worn by each subject with front surface asphericities of Q = 0 (conventional spherical surface), Q = -0.26 (similar to the average corneal asphericity) and Q = -0.51. The calculated average change in spherical aberration induced by each pair of contact lenses in photopic conditions was +0.02 D (Q = 0), -0.49 D (Q = -0.26) and -0.94 D (Q = -0.51). In mesopic conditions these same lenses induced an average change in spherical aberration of +0.01 D (Q = 0), -1.18 D (Q = -0.26) and -2.16 D (Q = -0.51). In this double-blind study, 12 adapted, low to moderate myopic rigid lens wearers wore each pair of lenses for one week and noted visual performance. With each pair of lenses we also measured the subject's visual acuity with high and low contrast logMAR charts. All measurements were conducted using the right eye at distance in photopic and mesopic conditions. When forced to select the lenses they would accept as compensation for participation in the study, most subjects (9 out of 12) chose the Q = 0 lenses, 3 subjects those the Q = -0.26 lenses and none of the subjects chose the Q = -0.51 lenses. Visual performance measures showed little difference between the Q = 0 and Q = -0.26 lenses. However, the Q = -0.51 lenses significantly reduced visual acuity in mesopic conditions with the low contrast acuity chart.