In the 1890s, opticians were reforming their practice against a body of medical practitioners who were increasingly attempting to specialise in, and monopolise, vision testing and spectacle dispensing. This article explores how and why vision testing became a subject of debate and how opticians were able to successfully set out their claims to professional authority in the face of medical competition. It argues that opticians created a scientific rhetoric distinctive from medical training by combining optics and anatomy. In response, medical practitioners attempted to consolidate the medicalisation of an area of the body through claiming completely new, and potentially unfounded, areas of expertise and medical jurisdiction. A study of the optician's role in the 1890s demonstrates the broader influence of fringe professions, commercial marketing and the public's receptiveness to the construction of expertise in enabling but ultimately inhibiting the medicalisation process, an outcome that medical practitioners had to grudgingly accept.