Contrast performance best with zero spherical aberrations

By using adaptive optics and physiological eye models, Pablo Artal and colleagues from Universidad de Murcia, Spain have determined that contrast performance peaks when spherical aberration is completely corrected.

An adaptive-optics based vision simulator that allowed for simultaneous manipulation of ocular wavefront aberration and measurement of visual performance was created. The simulator consisted of a wavefront sensor, an adaptive optics mirror and a visual testing path. Subjective measurements of contrast sensitivity in five subjects with different levels of naturally occurring spherical aberration, at 15 c/deg with a 4.8 mm pupil, were performed.

Contrast sensitivity was measured for spherical aberration values of -0.09, 0.0, 0.09 and 0.182 µm with the other naturally occurring aberrations of the eye present and corrected and with defocus varying from +0.5 to -0.5 D. The same levels of spherical aberration were compared in physiological eye models to establish tolerances to tilt and decentration and to verify through-focus performance.

Each subject experienced peak contrast sensitivity performance with varying levels of spherical aberration when their natural aberrations were present, however, the average contrast performance peaked with 0 µm of spherical aberration.

The researchers concluded that contrast performance is at its best when spherical aberration is completely corrected.