Analysis of changes of Kappa angle in patient with myopia of different position during Laser Assisted in-situ keratomi leusis (LASIK)

Objective To investigate the change of Kappa angle in patient with myopia of sitting and supine position during laser assisted in-situ keratomi leusis (LASIK).Method A total of 215 patients with myopic included 395 eyes who underwent LASIK were divided into low,middle and high myopia groups according to different diopters.The horizontal and vertical offsets of kappa angle in sitting position of preoperative analytical system examination were measured by Oculus Pentacam.During the operation the X and Y axis tracking modulation of ALLEGRETTO Wavelight Excimer Laster System were opened for getting horizontal and vertical offsets of kappa angle in supine position.All data were analyzed respectively.Results Kappa angle of 223 eyes (56.4％) were positive values in sitting position,and 343 eyes (86.8％) were positive values in supine position.The relationship between kappa angle and diopter was analyzed with one-factor analysis of variance.The differences of horizontal offsets of kappa angle in different position of three groups were no statistically significant (P ＞0.05),but the differences of vertical offsets of kappa angle of the three groups were statistically significant (P ＜0.05).There were significant differences in horizontal and vertical kappa angle between sitting and supine position by paired T test (P ＜0.05),and there were positive correlations.The offsets of kappa angle in sitting and supine positions had a significantly negative relation with the degree of myopia (sitting position R=-0.109,supine position R=-0.172; P ＜0.05).Conclusions There is correlation in horizontal and vertical offsets of kappa angle in sitting and supine positions.With the increase of the myopic degree vertical offset of kappa angle is increased.Clinicians should take into account different postures when refractive surgery need be performed. Key words: Kappa angle;  Myopia;  LASIK