Hermann von Helmholtz, increasingly fascinated by the epistemological question of perception, had turned his attention to the physiology of the senses in 1850.
Embarking on explorations in physiological optics, Helmholtz revolutionizes the field of ophthalmology in 1851 with the invention of the ophthalmoscope; an instrument used to examine the inside of the human eye.
This makes him world famous overnight.
His main publication, entitled Handbuch der Physiologischen Optik (Handbook of Physiological Optics), provides empirical theories on spatial vision, color vision, and motion perception, and is to become the fundamental reference work in his field during the second half of the nineteenth century.
His theory of accommodation will go unchallenged until the final decade of the twentieth century.