Compensation of corneal horizontal/vertical astigmatism, lateral coma, and spherical aberration by internal optics of the eye.

Both the anterior surface of the cornea and the internal optics (the posterior cornea, crystalline lens) contribute to the aberration of a wavefront passing through the eye. Artal, Guirao, Berrio, and Williams (2001) reported that the wavefront aberrations produced by the internal optics offset, or compensate for, the aberrations produced by the cornea to reduce ocular wavefront aberrations. We have investigated the wavefront aberrations of the cornea, internal optics, and complete eye on both the population and individual level to determine which aberrations are compensated and probable paths leading to that compensation. The corneal and ocular aberrations of 30 young subjects at relaxed accommodation were measured with the Topcon Wavefront Analyzer, which simultaneously measures refraction, corneal topography (videokeratoscope), and wavefront aberrations (Hartmann-Shack sensor). We found strong evidence for compensation of horizontal/vertical (H/V) astigmatism (Zernike term Z5) lateral coma (Z8) and spherical aberration (Z12). H/V astigmatism compensation is scaled for each individual, suggesting that it is actively determined by a fine-tuning process. Spherical aberration shows no individual compensation, suggesting that is a passive result of genetically determined physiology. Lateral coma shows individually scaled compensation, some of which may be attributable to eccentricity of the fovea.