Simplified subjective measurement method for visual acuity with Landolt ring

摘要

The method involves rotating a Landolt ring (1) of constant diameter at a distance from the subject which initially renders such rotation imperceptible. The distance is continuously reduced and the angle of vision enlarged until the opening (2) and its rotation are unambiguously discernible. The visual acuity is given by the product of the standard value and the quotient of the initial and final test distances. Alternatively a ring of variable diameter may be rotated at a constant distance until the rotation can be perceived.