Purpose: The purpose of the study is to assess changes in optical performance of the cornea in patients with keratoconus following treatment with corneal collagen crosslinking (CXL). Materials and Methods: One hundred and eleven eyes of 111 consecutive keratoconus patients with 12-month follow-up after CXL were included. The changes in the visual acuity, manifest refractive errors, and corneal topographic parameters were evaluated. Sirius dual-scanning corneal tomography was used to determine the effectiveness of CXL on each patient's total corneal optical quality; preoperative and 12-month postoperative measurements were analyzed over a 4-mm stimulated pupil and were compared with regards to higher order corneal aberrations (total amount of higher order aberrations [HOAs], vertical coma, horizontal coma, vertical trefoil, oblique trefoil, and spherical aberration), vertical and horizontal modulation transfer function (MTF), and Strehl ratio of point spread function (PSF). Results: At 12 months, there was a significant improvement in mean uncorrected visual acuity (UCVA) (P < 0.001), best corrected visual acuity (BCVA) (P < 0.001), spherical equivalent refraction (P = 0.007), and manifest astigmatic refraction (P < 0.001). The corneal topographic measurements revealed a significant decrease in the mean simulated keratometry-1, simulated keratometry -2, and maximum keratometry compared with the baseline measurements (P < 0.001, for all). In addition, there were significant improvements in mean root mean square error values for corneal total HOA (P < 0.001), vertical coma (P < 0.001), and vertical trefoil (P = 0.008) following CXL. Mean MTF and Strehl ratio did not change after CXL (P > 0.05). The improvement in UCVA significantly correlated with the changes in vertical trefoil (r = -0.191, P = 0.044), and the improvement in BCVA and the changes in manifest astigmatic correction were also significantly correlated (r = -0.247, P = 0.009) 12 months after CXL. Conclusions: CXL treatment for keratoconus led to an improvement in visual, refractive, topographic, and most corneal HOAs outcomes at the 12-month follow-up. However, these improvements were not enough to increase corneal MTF and the Strehl ratio of PSF.