The Effect of Head Tilt on Grating Visual Acuity Values

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  • Hisae Inagaki
    Faculty of Health and Medical Sciences, Aichi Shukutoku University

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  • 頭位の傾斜が縞視力に及ぼす影響

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Abstract

<p>Purpose: This study evaluated the effect of head tilt on grating visual acuity (VA) in consideration of ocular counter-roll (OCR).</p><p>Methods: Subjects were 5 eyes of 5 participants (mean age: 19.8 ± 1.6 years) with uncorrected VA of ≥1.5, astigmatism less than 0.75 D, and no ocular or eye movement diseases. In the grating VA experiment, the participant was required to detect the inclination of the grating targets displayed on a computer screen with 90.6% contrast, and the correct answer rate was obtained. The spatial frequencies of the gratings were set at 15, 17, 20, 24, 30, 40, and 60 cpd; and inclination was set to 0° (vertical), ±45° (oblique), and -90° (horizontal). Head position was set at 0° (vertical), ± 45° (oblique), and -90° (horizontal). To evaluate cyclotorsion, the participant's iris patterns were photographed under the same test condition for head position, and the rotation angles were measured. The correct answer rate and rotation angle were evaluated using the analysis of variance.</p><p>Results: (1) The head position did not affect grating VA when the spatial frequency was ≤ 24 cpd. (2) At 30 and 40 cpd, the oblique effect was observed with a head tilt angle of 0°. (3) The correct answer rate obtained at a head tilt angle of -90° was significantly lower than those at angles of 0° and ±45°. (4) Although OCR occurred in 10%-20% of the head tilt, it did not influence the oblique effect.</p><p>Conclusion: Grating VA should be measured at a vertical head position of 0°. When the head is tilted to ±45°, the presentation of the visual target needs to be adjusted to the inclination of the head position. When the head is tilted to a horizontal position of -90°, the visual target should be presented vertically rather than to the direction of the head position, and a possible underestimated grating VA should be considered.</p>

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