Pupillometry: the influence of gender and anxiety on the pain response.

BACKGROUND Studies suggest that the pain response may be evaluated using pupillometry and is influenced by factors such as gender and anxiety. OBJECTIVES The aim of this study was to use pupillometry to observe the effects of gender and anxiety on the pain response. STUDY DESIGN A randomized, prospective, clinical and interventional study. SETTING Center for Research on Pain at the Federal University of Maranhao, Brazil. METHODS Ninety-six patients were divided into groups according to their level of anxiety as indicated by the Beck questionnaire. Under photopic conditions and using retinography, these patients underwent pupillometry while a painful pressure stimulus of 1,500 kPa was applied to the middle phalanx of each patient's right middle finger using a pressure algometer. RESULTS The pupil diameter increased in response to pain in all study participants, regardless of gender and anxiety level; the average pupil diameter was 3.265 ± 0.028 mm before the painful stimulus and 4.31 ± 0.200 mm for the duration of the stimulus (P = 0.0251). There was no significant difference between the genders in the level of anxiety (P = 0.614). Regardless of gender, individuals with moderate to severe anxiety had higher average pupil diameters than individuals exhibiting mild or no anxiety (P = 0.019). Men had a higher average pupil diameter than women (4.53 ± 0.345 mm and 4.48 ± 0.358 mm, respectively); however, this difference was not statistically significant in the presence of moderate to severe anxiety (P = 0.072). LIMITATIONS The number of men with high anxiety was insufficient to create their own group. CONCLUSIONS The pupil dilation in response to a painful stimulus was similar in both genders. Additionally, regardless of gender, the average pupil diameter was greater in the presence of moderate to severe anxiety.