Outcome of corneal and laser astigmatic axis alignment in photoastigmatic refractive keratectomy

Purpose: To compare the refractive results of laser astigmatic treatment in eyes in which the astigmatic axes of the eye and laser are aligned by limb al marking at the 6 o'clock position and in eyes that are not marked. Setting: University Hospital and Clinics, Madison, Wisconsin, USA. Methods: This retrospective study comprised 143 eyes that had photoastigmat ic refractive keratectomy with the VISX Star excimer laser. The eyes were d ivided into marked (G1) and unmarked (G2) groups. Based on the preoperative astigmatism each group was subdivided into low astigmatism (less than or e qual to1.00 diopter [D]) and high astigmatism (greater than or equal to1.25 D). Early postoperative manifest refractions (1.0 to 2.5 months) were anal yzed. The Alpine vector analysis method was used to calculate the target in duced astigmatism, surgically induced astigmatism, difference vector (DV), magnitude of error (ME), angle of error (AE), and index of success (IS). Results: There was no significant difference between the groups in DV, ME, and IS. When the subgroups were analyzed, the DV and ME were comparable; th e IS in the G1 high astigmatism subgroup was significantly better than that in the G2 high astigmatism subgroup (0.22 +/- 0.08 and 0.29 +/- 0.04, resp ectively; P < .0001). There was comparable scatter of AE values; 30% and 36 % in G1 and G2, respectively, had an AE of 0. Similar scatter was observed in the subgroups. Of the eyes that had an AE of 0, 90% and 43% in the high astigmatism subgroups of G1 and G2, respectively (P < .05), had full correc tion of astigmatism. Conclusion: Limbal marking and subsequent eye and laser astigmatic axis ali gnment improved the refractive outcome of laser astigmatic treatment of gre ater than or equal to1.25 D. A preliminary report of an ongoing prospective randomized study of eyes that had laser in situ keratomileusis is included . Ur Cataract Refract Surg 2000; 26:1722-1728 (C) 2000 ASCRS and ESCRS.