Relationship between asphericity and spherical aberration of the human cornea with different corneal diameters

Abstract

Objective To evaluate the asphericity of the anterior and posterior comeal surfaces in myopic eyes with different corneal diameters.Methods It was a cross-sectional study.One hundred and sixteen eyes of 116 myopic or myopic astigmatism patients were enrolled.The preo perative spherical refraction was -1.25～-10.75 D,and the cyclindrical refraction was 0.00～-3.50 D.The Q-value and spherical aberration of the anterior and posterior corneal surfaces for different corneal diameters (6,7,8,9 mm) were measured with a Pentacam.The correlations between Q-value and spherical aberration,corneal refraction and central corneal thickness were investigated usiug a Pearson correlation,and a linear regression was used to establish the regressione quation of Q-value and spherical abberration.Results The Q6 mm,Q7 mm,Q8 mm,Q9 mm of the anterior corneal surfaces of the 116 eyes were -0.24±0.09,-0.29±0.09,-0.33±0.09,-0.39±0.10,respectively; posterior corneal surfaces were -0.12±0.12,-0.21±0.11,-0.30±0.10,-0.38±0.10,respectively.The Q-values of the anterior corneal surfaces were more negative than the posterior corneal surfaces,the differences were significant except the 9 mm (t=-10.35,-6.68,-3.46,P＜0.01).Positive relationships were found between the Q-value of anterior and posterior corneal surfaces for 6-9 mm corneal diameters (r=0.30,0.37,0.40,0.42,P＜0.01).For a 6 mm corneal diameter,the regression equation of the anterior corneal surface was SA=0.663Q+0.415,and the posterior corneal surface was SA=0.159Q-0.177.Positive relationships were also found between the anterior Q-values and cyclinder refractions for 6-9 mm corneal diameters (r=0.28、0.27、0.25、0.22,P＜0.05).Negetive relationship were found between the posterior Q value and comeal thickness for 7-9 mm corneal diameter (r=-0.18,-0.21,-0.24,P＜0.05).ConcIusion Both the anterior and the posterior corneal surfaces in myopic eyes were prolate.As the corneal diameter increased,the Q-values became more negative.The relationship between Q-value and corneal spherical aberration can provide more valuable instructions for refractive surgeons when designing aspheric ablation. Key words: Cornea; Myopia; Q-value; Spherical aberration