Minimum repetitions for stable measures of visual dependency using the dot version of the computer-based Rod-Frame test

Visual dependency is a condition where spatial orientation is mainly dependent on visual information. It can be affected in conditions such as vestibular disorders, brain injuries and neck pain including whiplash. Visual dependency can be assessed with a computer-based, dot version, Rod-Frame test (C-RFTdot) by measuring the deviation of a rod (comprised of two dots) from the true vertical within tilted frames at 18° in both clockwise and anticlockwise directions. However, the number of test repetitions differs between studies. The purpose of this study was to investigate the minimum number of repetitions to obtain stable C-RFTdot outcomes. Thirty-one asymptomatic subjects were recruited. With a frame tilt of 18° (clockwise and anticlockwise), the rod was pre-set at 20° in both clockwise and anticlockwise directions. The rod could be rotated, using a mouse, to a minimum of 0.01°. The clockwise and anticlockwise deviations from the true vertical were positive values and negative values, respectively. A session consisted of two measures of deviations of pre-set rod conditions in each frame. Their signed values were averaged for analysis. Eight sessions were conducted. The differences between the mean values of N−1 and N repetitions (2 ≦ N ≦ 8) were measured. Differences were similar across repetitions and the standard deviations tended to decline over repetitions. Intraclass correlation coefficients (ICC) for five and more repetitions became >0.8 in each frame condition. Hence, five was considered the minimum number of testing so that the C-RFTdot can give consistent measures of deviation from the vertical in asymptomatic healthy individuals.