Reliability study of the Visual Vertical in subacute stroke

Abstract

Visual vertical (VV) has been being increasingly used as a routine clinical assessment to identify alteration of verticality perception as a possible cause of postural disorders after stroke. This study aims to determine if the reliability of VV is sufficient to support a wide clinical use in neuro-rehabilitation for stroke patients monitoring. We assessed the inter- and intra-raters reliability and the inter-trials reliability. In a first study, 20 subacute stroke patients in neuro-rehabilitation unit were tested after a first hemispheric stroke. To evaluate the inter-rater reliability, VV was assessed the same day by 2 examiners whose degrees of expertise differed. The second examiner repeated the test the next day in order to investigate intra-rater reliability. VV orientation (mean, primary criterion) and uncertainty (standard deviation, secondary criterion) were calculated over 10 trials. Their reliability was quantified by the intraclass correlation coefficient [ICC], Bland-Altman plots and the minimal detectable change (MDC). The concordance between two examiners was quantified by Cohen's kappa coefficients ( κ ). In a second study, inter-trials reliability was assessed in 117 subacute stroke patients by ICC and SEM. In study 1, regarding VV orientation, inter-and intra-rater reliability were excellent (ICC = 0.979 and 0.982). The Bland-Altman plots and the MDC revealed a difference inferior to 2° between two tests. The concordance between two assessments for the diagnosis of abnormal VV orientation was absolute for the same examiner ( κ = 1; P < 0.05) and excellent between two examiners ( κ = 0.92; P < 0.05). As for VV uncertainty the intra-rater reliability was satisfactory (ICC = 0.836) but the inter-rater reliability poor (ICC = 0.211). In study 2, a high inter-trials reliability required a minimum of 8 trials (ICC = 0.909; SEM = 1.18°) for patients with contralesional VV bias, whereas a minimum of 6 and 10 trials were required for patients with ipsilesional VV bias (ICC = 0.896; SEM = 0.96) and patients with normal VV perception (ICC = 0.728; SEM = 1.13) respectively. The orientation of the visual vertical is a highly reliable criterion, which may be used both in research and routine clinical practice. VV orientation can be adequately assessed with 6 to 10 trials in subacute stroke patients. Ten trials are recommended when comparison between sub-groups of patients having divers VV biased perception is intended.