Optimum shadow-casting illumination for endoscopic task performance.

HYPOTHESES Task performance improves with the use of a balanced degree of shadow and illumination compared with no or maximum shadow contrast; and overhead shadow-casting illumination is better than side illumination. DESIGN The standard task entailed touching target points on an undulating surface by using a surgical hook. Each run consisted of 13 target points in a random sequence. Five settings were investigated: no shadow; 22%, 42%, and 65% shadow contrast created by overhead illumination; and 22% shadow contrast produced by side illumination. Each surgeon completed 3 runs with each setting in a random order. SETTING Research laboratory at the Surgical Skills Unit, Ninewells Hospital, Dundee, Scotland. PARTICIPANTS Ten surgical trainees. MAIN OUTCOME MEASURES Number of errors and execution time. RESULTS Shadow contrast settings had fewer errors than shadowless imaging (P<.001). Work with overhead 22% shadow contrast had a lower error rate than side illumination (P<.001). With overhead illumination, 22% and 42% shadow contrast were accompanied by a lower error rate than maximum shadow contrast of 65% (P<.001 and P =.005, respectively). No significant difference was found in the execution time. CONCLUSION Optimum endoscopic task performance is obtained with overhead shadow-casting illumination and a balanced degree of illumination and shadow contrast.