Two-octave change in stereoacuity testing recommended as threshold of real change

Researchers conducted this retrospective cohort study to determine thresholds for "real change" in stereoacuity measured using four current stereoacuity tests: at near using the preschool Randot and the near Frisby stereotests, and at distance using the Frisby-Davis distance and the distance Randot stereotests. They found that changes of less than two octaves could not be distinguished from test-retest variability and recommended the use of greater differences of at least two octaves to distinguish real change as measured by these tests, whereas a lesser change may well be within test-retest variability.

Subjects in the study were 36 patients ranging in age from seven to 76 years with any type of stable strabismus and stereoacuity measured with each of the four tests on two consecutive visits.