Laser in Situ Keratomileusis for Mixed Astigmatism Using a Modified Formula for Bitoric Ablation

Abstract

To evaluate the results of treatment of mixed astigmatism with laser in situ keratomileusis (LASIK) by means of a modified Chayet formula for bitoric ablation and personalized nomogram calculations. A retrospective study was conducted in 19 consecutive eyes of 13 patients who underwent LASIK treatment of mixed astigmatism with a mean sphere of +1.63-/+1.23 D and a mean cylinder of -3.55-/+1.17 D. The authors used the Schwind ESIRIS Laser platform. The ablation was shifted from the pupil center to the vertex normal of the cornea. Three months postoperatively, the mean sphere was 0.08-/+0.24 D and the mean astigmatism -0.45-/+0.31 D. At 3 months, an uncorrected visual acuity (UCVA) of 20/50 or better could be found in 100% of the eyes, and of 20/25 or better in 59%. All eyes were within -/+0.5 D spherical equivalent (SE) at 3, 6, and 12 months. No eye lost more than one line of best spectacle-corrected visual acuity (BSCVA). Postoperatively, the corneal wavefront showed a reduction of spherical aberrations and coma, which were analyzed at 4 and 6 mm pupil diameter. The postoperative higher-order aberrations decreased at 4 mm and increased at 6 mm pupil sizes after surgery. Modified bitoric treatment with the Schwind ESIRIS laser showed an excellent postoperative UCVA and BSCVA with applying external nomogram adjustments. The method demonstrated good predictability, safety, and effectiveness in the treatment of mixed astigmatism.