‘Tacit’ and ‘explicit’ knowledge, and their relation to expertise, have a long-standing importance within social studies of science and technology. At the centre of the development of thinking about these topics has been the work of Harry Collins and Robert Evans. In this article, we bring to bear observations of the work of people involved in grading eye disease, and their seeming display of expertise, tacit and explicit knowledge, on three thrusts identified in the work of Collins, and Collins and Evans. These thrusts are the following: (1) a concern with the appearance of tacit knowledge in the activities of experts, (2) a commitment to studying expertise as ‘real’ and substantive rather than attributed, and (3) a commitment to promoting the recognition and fostering the management of expertise by providing analytical distinctions regarding expertise and its reliance on tacit knowledge. By considering what is involved in the work of grading eyes, we relocate the interest in tacit and explicit knowledge, and their bearing on expertise, in how expert knowledge is displayed and made recognizable in and through courses of action and interaction.