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KMID : 1011420180230020143
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Journal of Korean Ophthalmic Optics Society
2018 Volume.23 No. 2 p.143 ~ p.149
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The Effect of Dissociating Prism on Lateral Phoria in Von Graefe and Howell Phoria Card Test
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Oh Kwang-Keun
Cho Hyun-Gug
Moon Byeong-Yeon
Kim Sang-Yeob
Yu Dong-Sik
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Abstract
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Purpose: To evaluate the influence of lateral phoria in the von Graefe test and Howell phoria card test according to the amount of dissociating prism.
Methods: Thirty subjects (mean age 23.83±3.16 years) underwent subjective refraction test and phoria test using dissociating prism. The von Graefe test was performed in a random order by placing a 12 Δ base-in (BI) measuring prism in front of the right eye and 6, 8, 10 Δ base-up (BU) dissociating prism in front of the left eye respectively. The Howell phoria card test was performed in a random order with the Howell phoria card and 6, 8 and 10 Δ BU in front of the left eye, respectively. Also, the influence of the dissociating prism on the lateral phoria was analyzed according to the vertical phoria.
Results: The lateral phoria measured with 6, 8, 10 Δ dissociating prism respectively was significantly decreased with increasing the dissociating prism in the von Graefe test at distance (decrease in exophoria, p<0.001). There was no significant difference in the von Graefe test at near (p = 0.290). In the Howell phoria card test, there were no significant differences in distance and near lateral phoria (distance p = 0.841, near p = 0.190). As a result of analyzing by vertical phoria type, there was no significant difference in all test. But there was significant difference between left hyperphoria and hypophoria group (p = 0.013 at distance, p = 0.010 at near) in von Graefe test.
Conclusions: The amount of dissociating prism has an influence on only the von Graefe test at distance, and the position of dissociating prism affects lateral phoria when there is vertical phoria. Therefore, It is recommended that the von Graefe test for the lateral phoria is carried out after correcting vertical phoria to improve the reliability, or placing the dissociating prism in front of the eyes with vertical phoria. This study also suggests that the Howell phoria card test may place a dissociating prism regardless of the type of vertical phoria.
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KEYWORD
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Phoria, Lateral phoria, Vertical phoria, Dissociating prism, Von Graefe, Howell phoria card, Exophoria
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