Landolt C

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.