Landolt Ring
The Landolt ring , named after the Swiss ophthalmologist Edmund Landolt , is a standard optotype for eye tests that is prescribed in the European standard EN ISO 8596 (as well as in the previously valid DIN standard DIN 58220) for measuring visual acuity . It is also suitable for examining children and illiterate people .
It is a circular ring with an opening, the outer and inner diameter being in a ratio of 5: 3 to each other. The opening is 1/5 the outer diameter of the ring. The circle can be represented with the ring opening in eight positions, namely in a straight direction (recess up, down, right or left) and oblique direction (recesses offset by 45 degrees to the aforementioned). During the eye test, the test object should recognize where the opening is.
The Landolt rings have the advantage over the traditionally used letters that cognitive recognition and similarity patterns only play a subordinate role. Compared to the E-hook , the probability of correctly guessing the position of the gap is only half as great at 12.5 percent.
If you can see a Landolt ring whose recess corresponds to a viewing angle of just one minute of arc (e.g. 1.45 millimeters from a distance of 5 meters), the visual acuity is 1.0.
literature
- Herbert Kaufmann (Ed.): Strabismus. With the collaboration of Wilfried de Decker et al. Enke, Stuttgart 1986, ISBN 3-432-95391-7 .
Individual evidence
- ^ W. Wesemann, U. Schiefer, M. Bach: New DIN standards for determining visual acuity . In: Ophthalmologist . No. 107 , 2010, p. 821-826 , doi : 10.1007 / s00347-010-2228-2 .