Test-retest variability of cyclodeviations measured using the double Maddox rod test

The double Maddox rod test is often used to measure cyclodeviations and to monitor change over time. The purpose of this study was to estimate test-retest reliability and the amount of cyclodeviation that would be considered real change using 95% limits of agreement. We retrospectively studied 86 clinically stable patients with double Maddox rod measurements 5-175 days apart (median, 69 days). The range of cyclodeviation at the first measurement was 6° incyclodeviation to 15° excyclodeviation. We calculated the half width of the 95% limits of agreement to be 4.7°, which means that a change of ≥5° in cyclodeviation would be considered a real change. The threshold of 5° should be used when assessing change between two measurements made with double Maddox rods.