The effect of head tilt angle in the roll plane on the virtual subjective visual vertical results in healthy adults

Background and Aim: The subjective visual vertical (SVV) is commonly considered as an indicator of the sense of orientation and attributed to the utricular function. The present study examined the impact of different head tilt angles on SVV among the normal individuals. Methods: SVV was measured in 47 normal participants (30 males and 17 females; mean +/- SD age: 22.14 +/- 3.46) using a virtual goggle and forced-choice paradigm and was applied twice in 0 degrees, 15 degrees, 30 degrees and 45 degrees to the left or to the right. In addition, difference in mean of SVV in zero and non-zero positions was compared. Results: There was a statistically significant difference between the mean SVV results of 0 degrees and 15 degrees (p. 0.001). The comparison of mean SVV results between 0 degrees and 30 degrees, and between 0 degrees and 45 degrees were not significant (p > 0.05). In addition, comparison of SVV results between rightward and leftward tilt of 15 degrees was statistically significant (p. 0.001). The latter comparison was not significant for 30 degrees and 45 degrees (p > 0.05). Conclusion: Our results showed that head tilt angle of 15 degrees have a substantial impact on the virtual SVV. These findings must be taken into account in the growing body of research that uses the SVV paradigm in clinical populations.