Influence of Stiles-Crawford effect on visual performance after laser in situ keratomileusis.

ABSTRACT

We evaluated the impact of the Stiles-Crawford effect (SCE) on visual performance following laser in situ keratomileusis procedures. This prospective study included 71 eyes of 36 consecutive myopic patients (mean age, 20.94±3.69 years). Ocular aberrations and contrast sensitivity were measured one month after surgery. The SCE was modeled optically as a filter placed in front of the eye, and then the modulation transfer functions (MTFs) and the predicted log contrast sensitivity were calculated from the measured wavefront aberration data. Then the visual Strehl ratio for MTF (VSMTF) was calculated. The results indicated that the computed MTF with SCE were superior to that without SCE. The predicted contrast sensitivity functions were underestimated about 20% when the SCE was not taken into account for the scotopic pupil. Moreover, the measured contrast sensitivity was not significantly different from that with SCE at 6, 12, and 18 cycles/deg spatial frequencies. According to the obtained VSMTF ratio, optical qualities of all eyes were underestimated with the range from 5% (0.02 log unit) to 65% (0.22 log unit) without SCE, and the average value is 41% (0.15 log unit). When only taking higher-order aberrations into account, the predicted postoperative visual performance would be different from the real values. The evaluation of postoperative visual performance from wavefront aberrations should consider not only the compensation relationship between defocus and spherical aberration but also the SCE.