Having spent earlier chapters considering how scientific instruments gave rise to new ways of seeing and how contexts for vision affected the observer, the following two chapters of this final section examine the eye itself. The eye is both an optical instrument and a conduit for acts of perception. In this, it is very like either the microscope or the telescope, both of which ‘see’ by focusing light through a lens and seem to have an active influence on what is observed. But the eye also sees from within the body of an observing human subject and is therefore always looking from specific contexts. The study of the eye has a long history before the nineteenth century. Yet as a distinct medical practice, as ophthalmology, it took hold during the nineteenth century. Indeed in theory and particularly in practice the second half of the century is the period of greatest activity; when Hermann von Helmholtz began to publish his Treatise on Physiological Optics while developing the ophthalmoscope, and when Edmund Landolt and Jonathan Hutchinson made optical disease the subject of popular lectures for the citizens of Paris and London.

What emerges from much of the published work on optics and ophthalmology, written either for a general audience or the specialist, is both a fascination with the eye's fallibility and an admiration for the complex adaptation that made it such a successful organ of sight.