Comparison of the AC/A Ratio by the Grdient Method and the Heterophoric Method in Normal Subjects

Lee, Se Youp

Abstract

To determine and compare the AC/A ratio in normal subjects, the AC/A ratio was measured by three different methods;near gradient method, distant gradient method and heterophoric method. The 33 normal subjects were enrolled in this study. All of them met the following criteria:(1)no known ocular disorders such as anisometropia, strabismus, and amblyopia.;(2)refractive error under -4D and corrected visual acuity more than 0.9.;(3)stereoacuity of 40 arc sec on Titmus test. The AC/A ratio was measured under full correction of the refractive error. Ages ranged from 6 to 25 years with a mean age of 16 years. The mean refractive error of the subjects was -1.33 D in right eye and -1.38 D in left eye. The near gradient method showed a mean AC/A ratio of 3.36:1 ranging from 1.33 to 4.67 ;the distance gradient method showed a mean ratio of 1.79:1 ranging from 0.67 to 3 ;and the heterophoric method showed a mean ratio of 5.71:1 ranging from 4.13 to 9. There was no significant difference in the AC/A ratio between the sexes and in the AC/A ratio between ages less than 11 years and more than 11 years. Different AC/A ratio values were obtained using three different methods. Among the three methods, the heterophoric method tended to give a higher value than the gradient method, and the near gradint method tended to give a higher value than the distance gradient method.