Toward the elimination of guessing bias in Landolt acuity testing

A subjective guessing bias has been claimed to be present in association with visual acuity testing using the classic circular Landolt ring. A semiautomated visual test system has been described previously which uses an angular version of the broken ring. Evidence is presented here which indicates that this version of the test object overcomes the problem of guessing bias and thus might prove to be not only a preferred "standard" or reference optotype but also an acceptable clinical optotype in its own right.