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KMID : 1159320120140040373
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Korean Journal of Vision Science
2012 Volume.14 No. 4 p.373 ~ p.380
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Relation between gradient and calculated AC/A ratios according to binocular vision types
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Kim Jae-Do
Kim Hyo-Jeong
Hwang Jeong-Hee
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Abstract
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Purpose: The two most commonly used clinical methods for determining AC/A ratio are gradient method and calculated method. Relation between results by these two methods has not been found in different binocular vision types. This study is to compare between gradient method and calculated method in the different binocular vision types. Methods: 164 subjects who have no the ocular disease, strabismus and ambylyopia were participated. Means of refractive error and age are S-2.34(±2.25)D C-0.98(±1.00)D for right eye and S-2.22(±2.15)D C-1.05(±1.06)D for left eye, and 20.84±0.96(6 to 41 years) years old respectively. All measurements were performed with full spectacle correction measured by Vision-K Auto-refractor®. Distance (3 m) and near (40 cm) heterophorias were measured using Howell phoria and card Howell- Kim phoria card respectively. Calculated AC/A ratios (CAC/A ratio) were decided by pupil distance(cm) +0.4 (near phoria - distance phoria) and by a half of difference between near phorias with -1D and +1D accommodative stimuli Gradient AC/A ratios (GAC/A ratio). Result: CAC/A ratio (5.07±1.55) was significantly higher than GAC/A ratio (t = 1.95, p < 0.001) for all subjects. CAC/A ratio was significantly higher than GAC/A ratio in orthophoric (t = 2.0, p < 0.001), basic esophoric(t = 2.16, p < 0.05) basic exophoric(t = 2.20, p < 0.01) and convergence excessive(t = 2.26, p < 0.01) types, but not significantly different in other groups. There was no significant correlation between two methods in the individual (r = 0.012, p > 0.05). Conclusion: For all subjects, CAC/A ratios were higher than GAC/A ratios, but there was no correlation between two ratios. The differences between two AC/A ratios were different by binocular types.
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KEYWORD
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Gradient AC/A ratio, Calculated AC/A ratio
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