| 摘要 |
PROBLEM TO BE SOLVED: To enable even the test in a bright room with good accuracy by arranging the optotype surface of a test optotype with inclination on a surface orthogonal with an axis connecting a test window and an optotype presentation position. SOLUTION: The optotype surface of an optotype disk plate is arranged to incline at an angleθwith the surface W orthogonal with the central axis 01 connecting the center of the test window 2 and the optotype presentation position P. A position where a virtual window 2' of the same diameter as the diameter of the test window 2 does not overlap on the test window 2 is assumed in order to determine the angleθ. The central axis 02 connecting the center of the virtual window 2' and the optotype presentation position P is considered and the intermediate central axis 03 of the angle formed by the central axis 02 and the central axis 01 in the optotype presentation position P is set. The optotype surface is so arranged as to intersect with the central axis 03 in the optotype presentation position P. The light which is made incident from the test window 2 and is reflected at the optotype surface does not, therefore, pass the test window 2 again and consequently, the reflected light at the optotype surface is no longer visible even when the inside of a casing is viewed from any positions of the test window 2.
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