Spherical Aberration and the Human Eye
The spherical aberration profile of the natural human lens is complex, and changes with age and during accommodation. In contrast, the cornea retains a stable amount of spherical aberration throughout life, with approximately 90% of the population with positive asphericity and 10% having negative asphericity.(1)

IOL Optics: Aspheric vs Spherical
There are various conditions in which one IOL design will perform better than another. In general a conventional spherical IOL can add another layer of aberration on top of the patient's own corneal aberration. Light that hits the lens on the periphery will be refracted more than the light that hits the center of the optic, producing blurred vision. In contrast, we can improve potential visual outcomes by using a lens with no inherent spherical aberration.

To have sharp vision — to focus all the light on one point — the curvature of the periphery has to decrease while the central curvature remains the same. These non-spherical, closer-to-ideal IOLs are called aspheric lenses. Aspheric optics are complex to manufacture (vs. conventional spherical IOLs), but the benefits are reduced spherical aberrations and clearer, sharper vision. In fact, studies have shown that aspheric IOLs can produce enhanced visual outcomes in both objective (point-spread function) and subjective (enhanced vibrancy of colors) measures. (2,3,4)

1. Holladay JT, et al, A new intraocular lens design to reduce spherical aberration of pseudophakic eyes. J Refract Surg., 2002 Nov-Dec;18 (6):683-91.
2: Altmann GE, Nichamin LD, Lane SS, Pepose JS. Optical performance of 3 intraocular lens designs in the presence of decentration. J Cataract Refract Surg. 2005 Mar;31(3) 574-85
3: Bellucci R, Morselli S, Piers P. Comparison of wavefront aberrations and optical quality of eyes implanted with five different intraocular lenses. J Refract Surg. 2004 Jul-Aug 20(4):297-306.
4: Packer M, Fine IH, Hoffman RS, Piers PA. Improved functional vision with a modified prolate intraocular lens. J Cataract Refract Surg. 2004 May;30(5):986-92.