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KMID : 1159320220240020093
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Korean Journal of Vision Science
2022 Volume.24 No. 2 p.93 ~ p.102
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Analysis on the Effectiveness of the Heterophoria Examination in Virtual Space Using a Stereoscope
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Park Tae-Young
Lee Hang-Seok
Koo Bon-Yeop
Mah Ki-Choong
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Abstract
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Purpose : To analyze the effectiveness of the phoria examination in a virtual space with a stereoscope compared to the conventional method based on the Howell card.
Methods : 51 subjects (20~39 years old) were selected and has no general disease, ocular disease or suppression. Also, stereopsis of the 40 sec or more, and unaided or corrected visual acuity of 1.0 or more with both eyes. The refractive power of the stereoscopic lens was +3.00, +5.00 and +10.00 D, and the distance between the optical centers was 62.00 mm. Based on the Howell card, a phoria examination target for conventional and stereoscope was produced.
The measurements of lateral and vertical phoria by the conventional and stereoscope were randomly performed at the working distances of 5 m, 40 cm, and 33 cm. Also, the calculated AC/A ratios were obtained.
Results : The lateral phoria (△) measured at 5 m, 40 cm, and 33 cm working distance by the conventional, +3.00, +5.00, and +10.00 D stereoscope was -1.18±1.71, +2.39±3.46, +2.23±3.36, +2.36±3.31 (5 m), -3.88±4.17, -4.92±5.92, -4.98±5.70, -4.91±5.58 (40 cm), and -5.53±4.82, -6.50±6.67, -6.49±6.59, -6.38±6.54 (33 cm), respectively. The vertical phoria (△) was -0.03±0.97, -0.03±0.99, -0.03±0.87, +0.02±1.00 (5 m), 0.00±0.92, -0.05±1.00, -0.09±1.01, -0.02±1.02 (40 cm), and -0.05±0.99, -0.01±1.00, -0.11±1.02, -0.05±0.99 (33 cm), respectively. The calculated AC/A ratios (Δ/D) were 5.18±1.24, 3.34±1.45, 3.38±1.37, 3.36±1.35 (40 cm), and 4.81±1.22, 3.30±1.41, 3.36±1.41, and 3.35±1.38 (33 cm), respectively.
Conclusion : In the phoria examination using a stereoscope, the depth perception of the implemented virtual space is different from the real space, so the effects of convergence excess at distance and convergence insufficiency occurred at near. In order to have a similar level to the real space, it is necessary to add the experimental clues to increase the perception of distance with the peripheral virtual space.
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KEYWORD
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AC/A ratio, Heterophoria, Howell phoria card, Stereoscope
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