Weight analysis of influencing factors of human angle Kappa

Abstract

Background Angle Kappa is the angle between the pupillary axis and visual axis,and it is a major consideration in corneal refractive surgery and strabismic surgery.Researches showed that age and refractive status affect angle Kappa value,and additionally,the measuring results of angle Kappa are associated with instruments.Objective This study was to investigate and weight the influences of axial length,anterior chamber depth and corneal curvature to angle Kappa.Methods A cross-sectional study was designed.Fifty health volunteers were included from Dec 2009 to Aug 2010,with the age of 18-38 years and average diopter of-1.0 D and best corrected visual acuity of 1.0.The horizontal and vertical angle Kappa was binocular measured with a testing machine designed by laboratory of School of Optometry & Ophthalmology Wenzhou Medical University.IOLMaster was employed to measure the ocular axial length,anterior chamber depth and corneal curvature radius.A multiple linear regression model was established to analyze the influences of axial length,anterior chamber depth and corneal curvature radius to angle Kappa.Results An efficacious regression equation was established as Y =15.554-0.587X1+0.724X2+ 0.232X3 with the independent variables as axial length(X1),anterior chamber depth (X2),corneal curvature (X3) and dependent variable as horizontal angle Kappa (Y) (R =0.788,R2 =0.621,P =0.000).Horizontal angle Kappa showed a negative correlation with axial length (b1 =-0.587,β1 =-1.002,P =0.000) and a positive correlation with anterior chamber depth (b2 =0.724,β32 =0.296,P =0.030).No significant correlation was found between corneal curvature radius and horizontal angle Kappa (b3 =-0.232,β3 =-0.068,P=0.338).A new regression equation was Y =14.235-0.622X1 + 0.824X2 after removed the corneal curvature variable (R =0.786,R2=0.618,P =0.000),with a negative correlation between horizontal angle Kappa and axial length (b1 =-0.622,β1 =-1.062,P＜0.05) or positive correlation between horizontal angle Kappa and the anterior chamber depth (b2 =0.824,β2 =0.337,P＜0.05).In addition,a multiple linear regression equation among 3 independent variables and dependent variable of vertical angle Kappa was Y =0.492-0.020X1 +0.038X2 +0.089X3 (R =0.436,R2 =0.191,P =0.000).However,no significant correlations were seen between vertical angle Kappa and axial length,anterior chamber depth or corneal curvature radius (all at P ＞ 0.05).Conclusions Ocular axial length and anterior chamber depth have an obvious influence to horizontal but not vertical angle Kappa.Axial length appears to have more influence to horizontal angle Kappa than anterior chamber depth. Key words: Angle Kappa; Axial length; Anterior chamber depth; Corneal curvature