PURPOSE: Because the clinical reasoning processes engaged in by practicing optometrists have not previous been investigated, until now, there has been no way of knowing whether models of clinical reasoning from other health professions can be transposed to optometry. The purpose of this study has therefore been twofold: making explicit the clinical reasoning processes of optometrists at both the "competent" and "expert" levels and comparing these processes to highlight the characteristics of clinical reasoning expertise. METHODS: Four competent-level optometrists and four expert-level optometrists participated in this qualitative study. Each optometrist performed a complete optometric examination on a preselected patient. Each of these examinations was recorded on a DVD video and followed by a feedback session, also captured on a DVD video. The feedback session was conducted using techniques inspired by a form of interview called the "explicitation interview," aiming to describe optometrists' mental actions and the time sequence of these actions throughout the examination. RESULTS: The results indicate that optometrists' clinical reasoning is patient centered and includes both analytical and nonanalytical modes of reasoning. When compared with a competent-level optometrist, an expert-level optometrist is more patient centered, formulates an earlier mental representation of the patient's clinical situation (including diagnosis formulation), plans examinations more thoroughly, is able to analyze and reflect during cognitively demanding tasks, and draws up his or her care management plan throughout the entire examination. CONCLUSIONS: The verbalization of optometrists' clinical reasoning processes represents a first step toward a better understanding of this competency. The impact of this research on optometric education is discussed. The results open doors to further research in the field, for example, toward defining the stages of clinical reasoning development among optometry students and professionals.