Kollner's.König bars rule

rule, Kollner's.König bars

Target used to measure visual acuity consisting of two bars on a white background. The length of each bar is usually three times its width but the space between the bars is always equal to the width of one bar. The smallest pair of bars that can be perceived as separate gives a measure of the acuity.
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann