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KMID : 1011420200250030273
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Journal of Korean Ophthalmic Optics Society
2020 Volume.25 No. 3 p.273 ~ p.282
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Comparison of Calculated and Gradient Accommodative Convergence/Accommodation Ratios in Binocular Vision Types
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Lee Yoon-Gyeong
Hong Sung-Il
Kwak Ho-Weon
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Abstract
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Purpose: This study aimed to obtain data for the examination and prescription of clinical trials. Subjects were divided into binocular vision types by the Howell card phoria method. We compared calculated accommodative convergence/ accommodation (AC/A) ratio and gradient AC/A ratio by using deviations according to fixation distance and lens additions.
Methods: The subjects in this study were 117 undergraduate students (84 males and 31 females) with an average age of 20.89±1.83 years. The binocular vision types were separated into seven groups by Morgan’s norm according to the Howell card phoria method and measured calculated AC/A ratio and gradient AC/A ratio.
Results: In terms of phoria changes according to fixation distances and additions, as the fixation distance neared, the groups of convergence insufficiency, basic exophoria, orthophoria and divergence insufficiency moved towards exodeviation but the groups of divergence excess, convergence excess, and basic esophoria moved towards esodeviation. The calculated AC/A ratio with accommodative convergence and proximal convergence appeared larger than the gradient AC/A ratio with only accommodative convergence. The differences of calculated AC/A ratio and gradient AC/A ratio showed statistically significant differences in the divergence excess (1 m p=0.049, 50 cm p=0.047, 33 cm p=0.034, 25 cm p=0.031), basic exophoria (50 cm p=0.000, 33 cm p=0.006, 25 cm p=0.037), orthophoria (50 cm. p=0.019, 33 cm p=0.021), convergence excessive (50 cm p=0.016, 33 cm p=0.030), basic esophoria (50 cm p=0.029, 33 cm p=0.024).
Conclusions: In all binocular vision types, the calculated AC/A ratios were larger than gradient AC/ A ratios. Therefore, when binocular abnormality is performed during a clinical examination, it is necessary to apply the calculated AC/A ratios and gradient AC/A ratios together.
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KEYWORD
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Binocular vision types, Proximal convergence, Calculated AC/A ratio, Gradient AC/A ratio, Howell card phoria method
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