Assessment of subjective visual vertical using the bucket test in adults with cochlear implants

Abstract Background Although cochlear implant (CI) surgery is generally considered a safe and successful procedure, the anatomical and physiological characteristics of the inner ear may lead to certain adverse effects on the vestibular system. Subjective visual vertical (SVV) reflects the deviation in an individual’s perception of the earth-vertical line, thereby providing information related to otolith-mediated perception of verticality. The aim of this study was to evaluate whether there is a difference in SVV between adults with CI and those without CI using the bucket test. Methods The study was conducted with a total of 60 participants aged between 18 and 30 years, including CI users ( n = 30) and age-matched normal-hearing (NH) individuals ( n = 30). The bucket test was used to assess SVV in all participants. During the test, the bucket was rotated five times clockwise and five times counterclockwise, and the mean value was recorded. For comparisons of quantitative variables between independent groups, the Student’s t-test was used when parametric assumptions were met; otherwise, the Mann–Whitney U test was applied. Results Among all participants, the median age of female participants was 25 (20.75, 28.25) years, whereas the median age of male participants was 23 (21, 30) years. No statistically significant difference was found between males and females in clockwise and counterclockwise bucket test results (Z = − 1.674, p = 0.094; Z = − 0.438, p = 0.661, respectively). Additionally, no statistically significant difference was observed between the groups (NH vs. CI) in clockwise and counterclockwise bucket test results (Z = − 0.244, p = 0.807; Z = − 1.158, p = 0.247, respectively). Despite the absence of a statistically significant group-level difference, nine CI users (30.0%) demonstrated a deviation greater than 3° in at least one rotation direction. Conclusions Among the long-term CI users included in this study, no statistically significant differences in SVV deviation were detected compared with NH participants or according to sex and rotation direction. However, because the study was cross-sectional and did not include preoperative or objective ear-specific vestibular assessments, these findings should not be interpreted as evidence of preserved utricular function following cochlear implantation. The Bucket Test may provide a practical bedside measure of SVV, but complementary objective vestibular assessments are required for a comprehensive evaluation.