Landolt ring
A test object used for measuring visual acuity consisting of an incomplete ring resembling the letter C. The width of the break and of the ring are each one-fifth of its overall diameter. The subject must indicate where the break is located, the break being positioned in any direction. The minimum angle of resolution corresponds to the angular subtense of the just noticeable break at the eye (Fig. L3). Syn. Landolt broken ring; Landolt C; Landolt test type. See Landolt broken ring chart.
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Fig. L3 Landolt ring
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