The primary objective of this study is to give the investigators practical experience using hand-held pupillometry (which is the measurement of pupil size) and to help them become proficient in its use and to gather data on the optimal times for dark adaptation when using the device. Participants will be people between the ages of 18-60 who do not have eye disease. The recruitment target is up to 50 patients. The study involves one visit lasting around 1.5 hours. The procedures involve the participant being seated in a darkened room for ten minutes for dark adaptation for 10, 20, and 30 minutes before the pupillometry procedure.