BACKGROUND The techniques of limbal relaxing incision (LRI) and photoastigmatic keratectomy (PAK) are both effective methods for correcting pre-existing astigmatism with cataract extraction, but no previous study has directly compared them. OBJECTIVE To compare the effects of limbal relaxing incision (LRI) and photoastigmatic keratectomy (PAK) on preoperative astigmatism and higher-order aberrations (HOAs) in eyes undergoing cataract surgery. METHODS Kitasato University Hospital, Japan. METHODS A retrospective study of eyes which had undergone phacoemulsification and intraocular lens implantation through an astigmatically neutral incision either accompanied by LRI (LRI group, 20 eyes) or followed after 3 months by PAK (PAK group, 27 eyes), to control pre-existing corneal astigmatism. RESULTS Among eyes that underwent LRI, manifest astigmatism (corrected to the corneal plane) averaged -1.72 +/- 0.95 D preoperatively and -0.98 +/- 0.58 D postoperatively. Corneal astigmatism averaged 2.03 +/- 0.49 D preoperatively and 1.34 +/- 0.60 D postoperatively. Among eyes that underwent PAK, manifest astigmatism averaged -2.02 +/- 0.64 D preoperatively and -0.70 +/- 0.58 D postoperatively. Corneal astigmatism averaged 2.30 +/- 0.81 D preoperatively and 1.05 +/- 0.36 D postoperatively. With regard to HOAs, in the LRI group, corneal HOAs averaged 0.172 +/- 0.051 microm (total aberrations for 4 mm pupil diameter) and 0.681 +/- 0.433 microm (total, 6 mm) preoperatively, but 0.172 +/- 0.053 microm (total, 4 mm) and 0.651 +/- 0.187 microm (total, 6 mm) postoperatively. In the PAK group, the corneal HOAs averaged 0.179 +/- 0.073 microm (total, 4 mm) and 0.679 +/- 0.314 microm (total, 6 mm) preoperatively, but 0.206 +/- 0.095 microm (total, 4 mm) and 0.816 +/- 0.380 microm (6 mm, total) postoperatively. The only statistically significant differences in the postoperative HOAs between LRI and PAK groups were in the S4 and S6 (spherical and spherical-like aberrations being bigger in the PAK group ).There were no vision-threatening complications in either group. CONCLUSIONS PAK is more effective than LRI in the control of pre-existing manifest astigmatism. LRI causes less accentuation of the spherical HOAs than PAK.