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KMID : 1159320130150030243
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Korean Journal of Vision Science
2013 Volume.15 No. 3 p.243 ~ p.251
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The Consideration of the method of determining cylinder power and cylinder axis in fogging test
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Kim Hyun-Il
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Abstract
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Purpose: This study was designed to investigate the method of determining based on the displacement of a blacker line seen by a subject in astigmatic fan without using cross cylinder if there is an error of the cylinder power and axis in fogging test. Method: 34 subject who had regular astigmatism between -1.25D and -1.5D was measured how much an error has occurred from the original correction value of cylinder power and axis. The precondition for this is that the cylinder axis was on purpose by off the axis of astigmatism and the cylinder power was on purpose -0.5D or -0.75D weaker and stronger than it should be. In the first method, in fogging situation, the cylinder axis was corrected and next the cylinder power was corrected. In the second method, in fogging situation, the cylinder power was corrected and next the cylinder axis was corrected. We compared error of the cylinder power and axis. Results: Error of the cylinder power and axis was smaller than the absolute value of 0.25D and respectively(including SD). Conclusion: In fogging test, following method can be used in astigmatic fan(radiating lines at ). (1) When the displacement value of a blacker line is less than , the cylinder power can be increased until a subject recognize that a blacker line moves to be apart from the position of the initial blacker line. Thereafter the axis can be rotated in the opposite direction of the displacement of a blacker line until a subject recognize that every line in astigmatic fan are equally dark. (2) When the displacement value of a blacker line is , the axis can be rotated in the opposite direction of the displacement of a blacker line until a subject recognize that every line in astigmatic fan are equally dark. (3) When the displacement value of a blacker line is more than , the cylinder power can be decreased until a subject recognize that a blacker line moves to be by apart from the position of the initial blacker line. Thereafter the axis can be rotated in the opposite direction of the displacement of a blacker line until a subject recognize that every line in astigmatic fan are equally dark.
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KEYWORD
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Fogging test, astigmatic fan, cylinder power, cylinder axis
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