Do Pupil Dilation and Analgesia Nociception Index Reflect Pain: a Pilot Study in Healthy, Conscious Volunteers

Pain assessment is crucial in clinical practice. Currently, subjective self-report is considered the most appropriate method to evaluate pain. Although several methods to assess pain objectively exist, the lack of a golden standard still remains. This pilot study assesses the changes in pupil dilation (PD) and the analgesia nociception index (ANI) as a measure of pain in healthy, conscious, male volunteers in a highly standardized and individualized environment. Nineteen subjects received three blocks of 4 individualized electrical stimulus intensities, ranging from no to severe pain. Subjects reported their perceived severity of each individual stimulus, enabling the comparison of changes in PD and ANI in relation to both administered stimulus intensities and perceived pain severities. PD and ANI were measured before and after each administration of a stimulus.