Abstract
Abstract: :
Purpose: To compare the change in anterior corneal higher order (3rd – 5th order) aberrations (HOA) induced by myopic and hyperopic LASIK. Methods: The study comprised 100 eyes (50 myopes and 50 hyperopes) who had undergone LASIK by one surgeon using a 9.5 mm Hansatome microkeratome and the Technolas 217 (Bausch & Lomb) scanning spot laser system (Planoscan–Software V2.9992). Third to fifth corneal HOA were computed for a pupil diameter of 6 mm using CTView (Sarver and Associates Inc.) from corneal topographic examinations (Orbscan II, Bausch & Lomb) preoperatively and 1 month postoperatively. Surgically induced changes in corneal HOA were calculated from the pre– and postoperative data. The mean preoperative spherical equivalent (SE) was –4.22±1.78 D (–1.25 to –8.00) in the myopic group (A) and +2.72±1.25 D (+0.25 to +5.00) in the hyperopic group (B). Statistical analysis of change in HOA was performed using the Wilcoxon test for matched pairs (p<0.05 with Bonferroni correction). For comparison between the two groups, a Wicoxon–Mann–Whitney U test was applied. Results: On average, total HOA RMS changed in group A by 0.167±0.180 µm (factor 1.53) and in group B by 0.341±0.341 µm (factor 1.89). Third order aberrations increased in group A by 0.095±0.181 µm (factor 1.43) and in group B by 0.319±0.321 µm (factor 2.20). The mean induction of vertical coma (Z 3,–1) was significant (p=0.02) in group A (0.081µm, factor 5.7), but not significant in group B (–0.96µm, factor 4.4; p=0.71). The mean change of 4th order aberrations was 0.136±0.128 µm (factor 1.56) in group A and 0.130±0.179 µm (factor 1.56) in group B. For primary spherical aberration (Z 4,0) the myopic group showed a significant increase (p<0.001) (0.130±0.120 µm, factor 1.6), while the hyperopic group showed a significant decrease (p<0.001) (0.317±0.158 µm, factor 0.76). Fifth order aberrations showed an increase in both groups which was higher in group B (0.069±0.120 µm, factor 2.46) than in group A (0.005±0.065 µm, factor 1.49). Conclusions: Both myopic and hyperopic LASIK ablations cause an increase in total anterior corneal HOA. Myopic and hyperopic LASIK have different patterns of change in HOA.
Keywords: refractive surgery: optical quality • refractive surgery: LASIK • refractive surgery: comparative studies