The International Tinnitus Journal

Exploring the Novel Impact of Vagal Nerve Stimulation on Pupillometry Measures in Tinnitus Patients

Henk M. Koning*, Wim E. Tuinebreijer

Background: Tinnitus patients may suffer from autonomic symptoms, which can be measured with pupillometry. Tinnitus treatment with vagal nerve stimulation can improve the complaints, and this improvement could be evinced by pupillometry measures. Objectives: This study aimed to assess the reliability of portable infrared pupillometry, investigate the impact of vagal nerve stimulation on pupillometry measures, and identify predictors of this impact using a comprehensive research methodology. Methods: Forty-nine tinnitus patients were investigated with a portable infrared pupillometer, and an X-ray of the cervical spine was performed. The pupillometry was compared with a second measure after treatment with vagal nerve stimulation. Multiple linear regression models were used to examine the association between cervical spine measurements, hearing loss at 2 kHz, and maximum constriction difference before and after treatment with vagal nerve stimulation. Logistic regression was performed to study the association between vagal nerve stimulation and sex, hearing loss at 2 kHz, and cervical spine measurements. Results: Inter-observer reliability was excellent for the baseline pupil diameter and moderate to good for the maximum constriction amplitude. The baseline pupil diameter and the maximum constriction amplitude increased after vagal nerve stimulation in patients with and decreased in patients without effect after treatment. Multiple regression shows a significant positive effect of hearing loss at 2 kHz and intervertebral disc space between the 6th and 7th cervical vertebra and a significant negative impact of the size of anterior osteophyte 5th cervical vertebra on the baseline pupil diameter difference between positive and negative therapeutic effects of vagal nerve stimulation. Logistic regression shows a significant positive effect of the male sex and of hearing loss at 2 kHz and a significant negative impact of the size of anterior osteophyte 5th cervical vertebra on the therapeutic effect of vagal nerve stimulation. Conclusion: Our study affirms vagal nerve stimulation’s potential to positively impact pupillometry measures. The excellent inter-observer reliability for the baseline pupil diameter and the significant increase in pupil diameter and maximum constriction velocity after vagal nerve stimulation provides reassurance and strong encouragement for further research.