[Lasik correction of compound myopic astigmatism with positive versus negative cylinder ablations]

To compare the predictability, efficacy, and safety of two methods of Lasik correction of compound myopic astigmatism: positive cylinder ablation versus negative cylinder ablation.

Twenty nine eyes of 19 patients were retrospectively analyzed. They had undergone Hansatome or ALK-e flap keratectomy, and a Technolas Keracor 217c laser ablation. Group 1 (14 eyes) was corrected with the positive cylinder program, group 2 (15 eyes) with the negative cylinder program. Spherical equivalent (SE), cylinder, vector analysis, and best corrected and uncorrected visual acuities (BCVA, UVA) were compared in the two groups. Minimum follow-up was 6 months.

The preoperative mean SEs for groups 1 and 2 were, respectively, - 7.09+/-3.36 D and - 8.05+/-2.27 D (NS). Mean cylinders were 1.73+/-0.88 (group 1) and +/-0.74 (group 2) D. Visual acuities were not statistically different in the two groups. Postoperative mean SEs were, respectively, - 0.57+/-1.58 D and - 0.68+/-0.88 D. Mean cylinder was, respectively, 0.57 +/- 0.54 D and 0.7 +/- 0.46 D in groups 1 and 2. Astigmatism induced by surgery, calculated by vector analyses was, respectively, 1.36 +/- 0.66 D and 1.54 +/- 0.56 D. Percentages of UVA above 20/25 were, respectively, 50% and 35%. None of those differences was statistically significant. One eye lost one line of BCVA.

The positive cylinder ablation method makes a larger optical zone of ablation possible with the same central deepness of ablation. We found that the predictability, efficacy, and safety of this technique compares well with the negative cylinder ablation in compound myopic astigmatism.