Controlled induction of spherical aberration with custom soft contact lenses.

BACKGROUND

This study investigated the non-invasive induction of spherical aberration (SA) levels consistent with complication-free wavefront-guided (WFG) refractive surgery using custom WFG soft contact lenses and quantified the resulting impact on visual performance.

METHODS

Twelve healthy individuals of typical military age (mean of 26.08 +/- 1.92 years) meeting the inclusion criteria of emmetropia (less than +/- 0.50 DS and less than +/- 0.50 DC) as measured by subjective refraction served as subjects. Five plano lenses were manufactured to induce a range of SA typical of those encountered after refractive surgery. The measured SA values over a 6 mm artificial pupil in these five lenses were -0.224 microm, 0.074 microm, 0.214 microm, 0.495 microm and 0.621 microm. For each subject, the level of total ocular aberrations through 10 Zernike radial orders over a 6 mm pupil was measured with a custom Shack-Hartmann wavefront sensor, while wearing each lens. Visual performance was evaluated using high contrast visual acuity (HCVA) measured through a 6 mm artificial pupil.

RESULTS

Custom WFG soft contact lenses can be manufactured to include the range of SA that occurs with complication-free refractive surgery (-0.20 microm to +0.60 microm) and produces a change in SA within a similar range when worn on the eye. High contrast visual performance with these lenses varied, depending on the amount of SA in each lens. Visual performance worsened with greater amounts of positive or negative SA and a quadratic fit to the data peaked at +0.209 microm.

CONCLUSIONS

Defined levels of SA can be manufactured and induced (non-invasively) with WFG soft contact lenses and their effect on logMAR high contrast visual performance can be measured. Results show that subjects' best logMAR HCVA occurs with the presence of positive residual SA. When designing the actual test lens, the targeted change in aberrations for each subject will likely be better achieved by first measuring the aberrations of a template lens on the eye and then compensating for unique subject dependent eye-lens interactions.