It is now more than 150 years since Hermann von Helmholtz’s ‘discovery’ of the ophthalmoscope in 1851. He called it an Augenspiegel (eye mirror): the name ‘ophthalmoscope’ (eye-observer) did not come into common use until three years later; in 1854. At the time Helmholtz, who was only 29, was a professor of physiology and he wanted to demonstrate to his students why the pupil of the eye sometimes appeared black and at other times light. 

Prior to his invention there was much speculation as to what lay behind the black hole of the pupil of the eye. Until 1810 there had been many theories about why the eye became luminous under certain conditions. Some thought that the fleeting luminosity was a phenomenon of phosphorescence; others speculated that light absorbed during the day gave off light at night, while others thought that it was the result of activity similar to a firefly and that it was electricity emitted by the retina. Bénédict Prévost, Professor of Philosophy at Montaubon in France, in 1810 explained that the luminosity could only be observed when light entered the eye from without.