Two smaller groups 5M to 2M for repetitive testing (20/25, 6/7.5 to 20/10, 6/3 equiv.).
Can be wall-mounted.
Practical for testing illiterate patients or testing in multiple languages.
The Broken Ring or Landolt C test uses a single optotype placed in different positions; up, down, left, right, and 45 degree positions in between. Because there is only one optotype, patients simply have to gesture which position they see the optotype facing. Landolt C is helpful for testing illiterate patients that are not familiar with the Roman alphabet. Landolt C vision test are considered one of the best among alternative visual acuity tests.