Participants
stature
Twenty surgeons with at least 2 years of experience in endocrine, head and neck, or vascular surgeries were recruited from a Swedish academic hospital; the effective sample size was 19 due to dropouts. The selection of surgical specialties was based on the similarity in surgical postures and the use of loupes. Due to the limited availability of eligible participants, the sample size was determined to the fullest extent that the circumstances allowed. Information regarding age, sex, stature, weight, and surgical experience was collected. Each participant was examined by an optician. After the experiment, each participant was provided with one pair of prismatic loupes of their choice, which they can continue using in their daily work. The study was approved by the Regional Ethics Review Board in Stockholm (Dnr: 2020–02161, extended from Dnr: 2014/1120–31). The trial was registered under the number ISRCTN34385943 in the ISRCTN registry. All participants gave their informed consent to participate in the study.