Eye tracking has become the gold standard in measuring human attention and information-processing behavior. As such, eye tracking in mixed-methods user experience (UX) research serves as an invaluable tool to learn about user needs and to create actionable insights for improving product and service design during the development cycle. Here, we discuss the iterative process that we used to improve the design of a decision aid (DA) developed to facilitate shared decision making. We explain the use of eye tracking during this process to examine how users processed the information provided by the DA. We also explain how we used eye tracking in a retrospective “think-aloud” protocol to gain insight about users’ needs. Our results show that user reactions captured by eye tracking can not only be used to optimize design decisions but also to gather user feedback about their information processing needs.