Landolt C
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A Landolt C, also known as a Landolt ring or Landolt broken ring, is an optotype, i.e. a standardized symbol used for testing vision. It consists of a ring that has a gap, thus looking similar to the letter C. The gap can be at various positions (usually left, right, bottom, top and the 45° positions in between) and the task of the tested person is to decide on which side the gap is.
The stroke width is 1/5 of the diameter, and the gap width is the same[1]. This is identical to the letter C from a Snellen chart.
