A recent survey1 conducted by Bausch & Lomb highlights eye care practitioners' perceptions of spherical aberration (SA). Two significant findings include the fact that 97% of doctors agree that SA impacts the quality of their patients' vision, and that 91% of doctors believe that SA is prevalent among their patients. Clearly, SA is a significant problem – one which manufacturers are attempting to address with new contact lens designs. As eye care practitioners, our patients trust us to help them optimize their vision. In the past, we have concentrated our efforts on lower-order aberrations such as defocus and astigmatism, which impact where light focuses on the retina. Higher-order aberrations, which determine how well those light rays are focused, were a problem we just didn't have the tools to effectively measure. However, recent technological advances have brought the ability to understand the most dominant higher-order aberration – spherical aberration (SA) – within our reach. To engender a greater understanding of SA, the significant visual challenges it poses, and the options for correcting it, we have prepared a series of informational emails to be sent out regularly over the next two months. Spherical aberration is a dominant higher-order aberration inherent to the human optical system. SA results in the degradation of image quality. Because the magnitude of SA increases as the pupil diameter increases, it is especially troublesome in low-light conditions or at night (which is why SA has commonly been called "night myopia"). SA is caused by the eye's innate shape and physiological structure, which interferes with how precisely light converges to a focal point on the retina. This is referred to as inherent SA, and it is present in nearly 90% of all people, including those with 20/20 vision (on average, +0.15 microns of positive inherent spherical aberration).2 Inherent SA can be further convoluted by the optical aberration introduced by contact lenses (referred to as induced SA). The magnitude of the induced SA from a standard spherical lens is typically a function of the amount of defocus correction within that contact lens and varies power by power. bausch.com/demandvision Aspheric contact lenses are indeed capable of reducing the visual degradation caused by both inherent and induced SA. However, not all aspheric lenses are the same, and different aspheric designs have been developed to accomplish varying objectives. It is important that we understand these differences. Some products claim to have an aspheric design but they are actually intended to improve fitting performance only. These designs have nothing or little to do with optical performance and feature the asphericity on the posterior side of the lens to simply accommodate the surface of the eye. Aspheric designs focused on improving the optical performance apply the asphericity to the anterior side of the lens, adjusting it to reduce inherent and induced positive SA levels. When done appropriately, this can increase contrast sensitivity and image crispness, especially in low lighting. The enhanced aspheric optics of the Bausch & Lomb PureVision® contact lens represents the leading edge of such designs. Instead of applying a universal -0.15 microns correction across all powers, the PureVision lens design also considers the amount of induced SA for each given lens' power. By automatically adjusting the anterior asphericity of the lens, by power, to preemptively reduce SA, PureVision effectively reduces both inherent and induced aberration – the only spherical silicone-hydrogel lens to do so. The ability to address both lower-order AND higher-order aberrations truly is a revolutionary development in vision correction. We will be discussing this compelling new opportunity to improve patient visual quality at length in the next four e-newsletters. Topics include 1) a detailed discussion of SA, 2) how wavefront science enables us to better measure SA, 3) the PureVision lens' enhanced aspheric design, and 4) the importance of balancing lens optical design, material properties, and surface characteristics for patient success. Our goal is to enable you to better understand the subtle nuances associated with SA, and to better deliver the visual outcomes both you and your patients desire. Sincerely, Paul M. Karpecki, OD If you miss any issues in this series you can go to our archives on www.bausch.com/enewsarchives. 1 Data on file, Bausch & Lomb. 2 Thibos LN, et al. J Opt Soc AM A. 2002; 19:2329-2348 © 2006 Bausch & Lomb Incorporated. ®/™ denote trademarks of Bausch & Lomb Incorporated. 530-1588.