In addition to these “monochromatic” aberrations, images produced by white light may also be degraded by chromatic aberration, the spreading apart of colors of white light by a lens system. This effect is caused by dispersion, by which the index of refraction of a material medium may vary with the wavelength of the light passing through it. Just as a prism bends blue light more strongly than it bends red light, in practice, a convex lens will create a focal point for blue light anterior to the one for red light, so the eye is typically about 0.5 D more myopic for images formed in blue light than in red light. This disparity is the basis for the Lancaster red-green (“duochrome”) test for accommodative control (see the Quick-Start Guide).
Excerpted from BCSC 2020-2021 series : Section 3 - Clinical Optics. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.