An Evaluation of Two Different Methods of Marking the Horizontal Axis during Excimer Laser Keratorefractive Surgery for Myopic Astigmatism

Abstract

Abstract: : Purpose: In treating astigmatism it is important to properly align the cylinder axis. A treatment off the desired axis by even a small degree may reduce the treatment efficacy. One excimer laser system allows the surgeon to align the ablation pattern to correct for eye torsion in the supine position. We evaluate the efficacy of two different methods of marking the horizontal axis on the outcomes of excimer laser keratorefractive surgery for myopic astigmatism. Methods: A retrospective chart review was conducted on 65 eyes of 39 patients who underwent laser refractive surgery for myopic astigmatism. Patients with manifest astigmatism of 0.75D and greater were marked with a surgical marking pen at the 3:00 and 9:00 limbus to identify the horizontal axis. In one group (38 eyes), marks were placed with the patient seated on the edge of the bed immediately before positioning under the laser ("laser room group", mean preop astigmatism 1.78D + 0.83D). In the other group, marks were placed at the slit lamp with the slit beam set at 180 degrees as a reference ("slit lamp group", mean preop astigmatism 1.75 D + 1.08 D). All treatments were performed with the ALCON LADARVision excimer laser system. Postop mean manifest cylinder, reduction in cylinder, uncorrected visual acuity (UCVA) and best-corrected visual acuity (BCVA) were evaluated for both groups. Results: Mean postop astigmatism was 0.47D + 0.37D in the laser room group and 0.54D + 0.36D in the slit lamp group (p=0.494, NS). Mean reduction in astigmatism was 1.31D + 0.71D in the laser room group and 1.21D + 1.03D in the slit lamp group (p=0.657, NS). Cylinder was reduced by 71.9 + 19.3% from preop in the laser room group compared to 62.1 + 28.6% in the slit lamp group (p=0.104). There was no significant difference in the UCVA or BCVA between the two groups. In subset analysis, patients with a mean preop astigmatism of less than 2.00D had a mean reduction in astigmatism of 0.95D + 0.45D in the laser room group vs 0.60D + 0.40D in the slitlamp group (p=0.019). Conclusions: Overall, there was no significant difference between postop mean cylinder, reduction in cylinder, UCVA or BCVA between the laser room and the slit lamp groups. However, in patients with a mean preop astigmatism under 2.00D, the laser room group experienced a significantly greater mean reduction in astigmatism compared with the slit lamp group. Surgeon handedness or other factors may play a role. Larger numbers and longer followup will determine whether this difference is of clinical significance.

Keywords: refractive surgery • astigmatism • myopia