Inter-subject variability of through-focus visual acuity with induced spherical aberration

Investigative Ophthalmology and Visual Science
Eloy A. Villegas, Lucía Hervella, Pablo Artal
Purpose: To determine the differences in the through-focus visual acuity curves between subjects looking through induced values of spherical aberration used to extend depth-of-focus.
Methods: An Adaptive Optics Visual Simulator (VAO, Voptica SL, Murcia, Spain) was used to measure the through focus visual acuity (VA) from +0.50 to -3.0 D, in steps of 0.50 D, in 14 eyes with paralyzed accommodation for different optical conditions. (1) correction of spherical aberration as the baseline condition, (2) two values of induced negative spherical aberration (SA) of -0.15 and -0.30 µm (for 4-mm pupil). The inter-subject means and the 95% confidence intervals (CI), calculated as 1.96*SD, were estimated for all defocus values.
Results:The mean values of LogMAR (and CI) at far were -0.12 (CI, ±0.09), 0.02 (CI, ±0.12) and 0.21 (CI, ±0.32), at intermediate distance (1.5 D) were 0.11 (CI, ±0.24), -0.01 (CI, ±0.16) and -0.02 (CI, ±0.10) and at near distance (3.0 D) were 0.48 (CI, ±0.49), 0.22 (CI, ±0.37) and 0.11 (CI, ±0.17) for the baseline, -0.15-µm SA and 0.30-µm SA profiles respectively. Inter-subject variability of VA, expressed as CI, at far distance presented the largest value of CI for 0.30-µm SA while at intermediate and near distances was for the baseline condition. The CI values ranging between ±0.1 and ±0.4 LogMAR for all defocus values in both values of induced SA.
Conclusions:The induction of spherical aberration provides quite different visual performance depending on each subject. When SA is induced either in LASIK procedures or with IOLs, preoperative visual simulation using adaptive optics instruments, such as VAO, would allow the customization of the precise SA value to improve patient quality of vision after surgery.