Mobile phone app Vs bucket test as a subjective visual vertical test: a validation study

The SVV tests the ability of a person to perceive the gravitational vertical. A tilt in SVV indicates vestibular imbalance in the roll plane, and thus injuries to the utricle or its connecting nerves. A validated bedside method (et, al., 2009, 72(19):1689-1692, Neurol, Zwergal) is the bucket method, in which the subject estimates the true vertical by attempting to properly align a straight line visible on the bottom of a bucket that is rotated at random by the examiner. In our study, the subjects need to align the plumb line on the Visual Vertical iOS app to the vertical direction. Measurements of the SVV were made in 22 healthy subjects (16 females and 6 males). Each subject conducted 10 iterations of bucket test and 10 iterations of iOS app test. The reliability and validity of the iOS app was analyzed by SPSS21. Cronbach's α for the plumb line method was 0.976, and the iOS app was 0.978. Statistical comparison of SVV values measured by the iOS app and the bucket method showed no significant difference in distribution (Mann Whitney U test U = 0.944). The Visual Vertical iOS app is an effective and accessible substitute to the plumb line for the measurement of the validated bucket test.