Achieving a better understanding of the clinical reasoning process is an important approach to improve patient management and patient safety. Although clinical psychologists have used talk-aloud or stimulated recall approaches, these methods have biases. Recently, researchers have been exploring eye-tracking technology to gain "live" insight into clinicians' reasoning processes in certain fields of medicine (radiology, dermatology, etc.). We present a systematic review of eye-tracking literature used for clinical reasoning. We performed a literature search using the terms "eye" or "gaze tracking", "clinical" or "diagnostic reasoning", and "physician" in Pubmed, Embase, Psychinfo, Web of Science and ACM databases. Two investigators screened the abstracts, then full-text articles to select 10 pertinent studies. The studies evaluated medical decision making in four different medical domains using mostly experimental, observational approaches. A total of 208 participants were enrolled for the selected experiments. Paths for further studies are discussed that may extend the use of eye trackers in order to improve understanding of medical decision making.