Influence of Different Hinge Chord Length on High Order ...

Abstract

Background With the widespread application of LASIK, the surgery is accepted by both doctors and patients for its safety, reliability and indolence. However, there are up to 10%-15% of patients experience vision quality problems after LASIK such as glare, halo and decreased contrasts sensitivity despite of excellent uncorrected visual acuity. The existing ablation profiles of excimer laser can only correct lower order aberrations such as myopia, hyperopia and astigmatism, but induce additional imaging aberrations into the optical system. This is a major cause of the observed deterioration of visual quality after such corrections. LASIK is the most mainstream of the excimer laser surgical correction of myopia. LASIK needs to make a corneal flap, which is resetted after stroma cutting. The biggest weakness of LASIK is caused by a series of complications, including an additional high order aberrations brought by corneal flap. With the improvement of living standards, it is the more urgent problem to solve the visual quality brought by refractive surgery. With depth study of wavefront aberrations, doctors realize that the change of visual quality and the changes in wavefront aberrations have a close relationship. Many articles reported that wavefront aberrations increased after LASIK, especially higher order aberrations increased and the aberration increased significantly with increasing of the pupil’s diameter. This study explores the source of higher order aberrtions by hinge chord length of corneal flaps.Objective To compare the change of high order aberrations with time factor and influence of different hinge chord length on high order aberrations of LAISK in low to moderate myopia. Methods This study was taken of 40 low to moderate patients. The cases received LASIK by wide hinge chord length and narrow hinge chord length at random. C7, C12, RMSH were evaluated at preoperative and postoperative 1 month,3month,6month.Results (1)①In wide hinge chord length group, RMSH has an upward trend at post-op lm and post-op 3m (P<0.01), and reaches a peak at post-op 3m. There is a slight decline at post-op 6m with the mean is still higher than pre-op (P<0.05).②In wide hinge chord length group, C7 has an upward trend at post-op lm and post-op 3m (P<0.01), and there tends to be stable at post-op 6m (P>0.05) with the mean is still higher than per-op.③In wide hinge chord length group, C12 has an upward trend at post-oplm and post-op 3m (P<0.01), and there is a slight decline at post-op 6m (P<0.05) with the mean is still higher than pre-op. (2)①In narrow hinge chord length group, RMSH has an upward trend at post-op lm and post-op 3m (P<0.01), and reaches a peak at post-op 3m. There is a slight decline at post-op 6m with the mean is still higher than pre-op (P<0.05).②In narrow hinge chord length group, C7 has an upward trend at post-op lm and post-op 3m (P<0.01), and there tends to be stable at post-op 6m (P>0.05) with the mean is still higher than pre-op.③In narrow hinge chord length group, C12 has no change in trends over time(P>0.05). (3) Preoperatively, there were no significant statistical differences of C7 (P>0.05) between two groups. Postoperatively, there were significant statistical differences of C7 (P<0.01), and the mean of wide hinge chord length group was lower than narrow hinge chord length group. (4) There were no significant statistical differences of C12 preoperatively and Postoperatively (P>0.05). (5) Preoperatively, there were no significant statistical differences of RMSH (P>0.05) between two groups. Postoperatively, there were significant statistical differences of RMSH (P<0.01), the mean of wide hinge chord length group was lower than narrow hinge chord length group. Conclusions (1) In wide hinge chord length group and narrow chord group, RMSH has an upward trend at post-op lm and post-op 3m (P<0.01), and reaches a peak at post-op 3m. There is a slight decline at post-op 6m with the mean is still higher than pre-op (P<0.05). The change trend of C7(coma) is like the trend of RMSH. C12(spherical aberration) has different change trend. (2) Hinge chord length of coneal flap have influence on high order aberrations of LASIK in low to moderate myopia. The high order aberratioans of wide hinge chord length was lower than narrow hinge chord length, mianly for the influence of C7, little for C12.