In this informational series, we have discussed the eye care profession’s growing understanding of spherical aberration (SA), as well as the aspheric contact lens technologies designed to address this condition. Click on this link to view past issues of the series www.bausch.com/enewsarchives. In this issue, we will explore how the enhanced aspheric design of the Bausch & Lomb PureVision contact lens compares to the lens designs of some other brands.

Aspheric lens designs can be used to correct the inherent SA present in the majority of eyes. As indicated in a recent survey¹ conducted by Bausch & Lomb, 93% of doctors believe that naturally occurring SA should be corrected. Fortunately, it is a condition that can be reduced with some aspheric contact lens designs. However, not all aspheric lenses are the same, and different designs have been developed to accomplish varying objectives. Some aspheric designs might be intended to improve fitting performance. These designs may then feature the asphericity on the posterior side of the lens to accommodate the surface of the eye, and will have little or no effect on spherical aberration. Designs primarily focused on improved optics apply the asphericity to the anterior surface of the lens, adjusting it to reduce the average inherent positive spherical aberration levels found in the population. This can increase contrast sensitivity and image crispness, especially in dim lighting.

The enhanced aspheric optics of the PureVision lenses represent the leading edge of silicone-hydrogel lens designs. Instead of applying a universal correction across all powers, this design also accounts for the amount of induced spherical aberration for each given lens’ power. PureVision lenses are designed to reduce the amount of positive spherical aberration of the eye – the only silicone-hydrogel lens to do so. For example, a clinical evaluation was conducted and revealed the advantages of PureVision optics. Cohorts of twenty subjects were dilated to achieve a minimum 6.0 mm pupil diameter, and baseline spherical aberration was measured using a Bausch & Lomb Zywave^® Aberrometer. Then different contact lenses (including PureVision, Night & Day, Acuvue Advance, Acuvue Oasys, and O₂OPTIX, at both –1.00D and –5.00D) were inserted into one eye in random order, and the aberration measurement was repeated. Results are presented as the change from baseline compared to the spherical aberration reported for the general population.²