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KMID : 1159320160180040577
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Korean Journal of Vision Science
2016 Volume.18 No. 4 p.577 ~ p.585
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Comparative Analysis of measured distance and near heterophoria values of myopia-exophoria with increased vertex distance
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Kim Hyun-Il
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Abstract
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Purpose: This study was intended to analyze the changes of distance and near heterophoria values of myopia-exophoria with increased vertex distance and to obtain the useful clinical data for binocular vision test.
Methods: Using a trial frame and trial lens, distance and near heterophoria values were measured using a Modified thorington(MT) test, Howell card(HC), Maddox rod(MR) in 20 subjects of myopia-exophoria. Heterophoria values were measured based on vertex distance of 12 mm with increased vertex distance by 5 mm, 10 mm, and 15 mm.
Results: With increased vertex distance by 5 mm, 10 mm, and 15 mm, the changes of distance and near mean heterophoria values using a MT(distance) were 0.09±0.12△, 0.20±0.10△, 0.31±0.11△ (F=20.07, p=0.00), MT(near) were 0.09±0.12△, 0.10±0.15△, 0.21±0.20△(F=3.62 p=0.03), a HC(distance) were 0.06±0.11△, 0.14±0.13△, 0.26±0.19△(F=9.48, p=0.00), HC(near) were 0.06±0.11△, 0.09±0.12△, 0.19±0.18△(F=4.42, p=0.02). MR(distance) were 0.04±0.09, 0.10±0.13, 0.23±0.16△(F=10.97, p=0.00), MR(near) were 0.03±0.08△, 0.05±0.10△, 0.11±0.13△(F=3.72, p=0.03), there were statistically significant difference.
Conclusions: Measuring the heterophoria values of myopia-exophoria with increased vertex distance, there were statistically significant a reduction of distance/near exophoria values, and more changes at distance than at near. The reason is that BO prismatic effect was induced by decentration of spherical lens with increased vertex distance at distance and besides BI prismatic effect induced by decentration of spherical lens with increased vertex distance at near, additional exophoria was caused at near. Consequently, the vertex distance should be kept constant at binocular vision test and an attention is required for trial frame in order not to move forward.
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KEYWORD
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Vertex distance, Prismatic effect, Heterophoria value
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