[Determination of visual acuity using optokinetic nystagmus. A newly developed instrument based on Günther's principle].

The two most important methods used for objective determination of visual acuity are those of Ohm-von Romberg and Günther. A newly developed instrument based on Günther's principle is described which combines the advantages of both methods. Using a Leitz projector and a specially designed accessory unit, a constantly moving screen of dots measuring 64 X 64 cm is projected. The setting was standardized on the basis of 358 eyes with visual acuities ranging from finger counting to 1.0. The correlation between the measured distance (from screen to patient) at which an optokinetic nystagmus was just induced and visual acuity was r = 0.98 over the entire visual acuity range. The visual acuity to be expected can be read off from the diagrams or a table, with a scatter range of +/- 1 sigma, +/- 2 sigma, or +/- 3 sigma. The relevant literature is discussed. Replication of the accessory unit described can be recommended.