Hyperhidrosis is thought to result from excessive stimulation of sweat glands due to increased sympathetic activity
however, data on systemic responses following bilateral thoracic sympathectomy as the definitive treatment have not yet been sufficiently evaluated. This study, designed as a prospective cohort investigation, included 24 patients who underwent sympathectomy for palmar and axillary hyperhidrosis at our center in 2023, along with an age-matched control group of equal size. In the sympathectomy group, pupillometry measurements were performed 1 day before surgery and on the 7th postoperative day, while the control group underwent measurements at corresponding intervals. Data from the sympathectomy group were analyzed both preoperatively and postoperatively and compared with the control group. According to the Hyperhidrosis Disease Severity Scale, all patients had severe hyperhidrosis. Sympathectomy was performed at the T3 level in 9 patients and at both T3 and T4 levels in 15 patients. The postoperative satisfaction rate was recorded as 95.8%. No statistically significant differences were observed between preoperative pupillometry measurements of the sympathectomy group and those of the control group. However, when comparing preoperative and postoperative data within the sympathectomy group, significant differences favoring increased parasympathetic activity were noted in the latency of contractions and photopic low values (p = 0.016 and p = 0.038, respectively). Our study is one of the pioneering works to objectively demonstrate, through a quantitative method, that sympathectomy for hyperhidrosis enhances the parasympathetic system response in the ocular region.