Landolt C

The Landolt ring, named after the Swiss ophthalmologist Edmund Landolt, is an optotype for eye tests, which is the European standard EN ISO 8596 (as well as in the previously applicable DIN standard DIN 58220 ) prescribed for the measurement of visual acuity. It is also suitable for the study of children and illiterates.

There is a circular ring with aperture, outer and inner diameters are to each other in the ratio 5:3. The aperture is 1/ 5 of the outer diameter of the ring. The circle can be represented by the ring opening in eight positions, namely in a straight line ( cut- up, down, right or left) and oblique direction (recesses by 45 degrees to the aforementioned offset ). At the sight test the examinee should see where the opening is located.

The Landolt rings have the advantage that cognitive recognition and similarity patterns play only a minor role from the characters traditionally used. Compared to the E- hook is the probability to guess the position of the gap correctly, only half as large.

If you can recognize a Landolt ring, the recess ( ie, for example 1.45 millimeters from 5 meters ) corresponds to a visual angle of one minute of arc, the visual acuity is 1.0.