Soft contact lenses with different levels of third-order spherical aberration were tested in two samples of subjects aged between 20 and 45 years: 18 emmetropes and 19 myopes. Contrast sensitivity was measured at 12 cycles/degree to determine the optimal lens spherical aberration required by each individual. The optimal third-order coefficient was found to be negative on average in both refractive error groups. Myopic subjects required contact lenses with more negative spherical aberration than did emmetropes. The optimal aberration was also found to become increasingly negative with aging. The rate of this age-related change was faster in the myopic group. In comparison with aberration-free soft contact lenses, an improvement in contrast detection threshold of more than 25% was observed with optimal spherical aberration in half of the myopic subjects.