[From otoscope to ophthalmoscope and back. The interwoven history of their invention and introduction into medical practice. Pictures from the history of otorhinolaryngology, illustrated by instruments from the collection of the Ingolstadt German Medical History Museum].

Friedrich Hofmann, medical officer in Burgsteinfurt, Westphalia, Germany, in 1841 described a concave mirror with a central aperture in it as the ideal instrument that allowed reflecting and focussing light into the external auditory canal and simultaneously inspecting the tympanic membrane without obstructing either the light or the view. He recommended his device also for the inspection of other concealed regions of the body. His invention was referred to by Martell Frank in his textbook of otology in 1845, but otherwise attracted no attention. Hermann Helmholtz, physiologist in Königsberg, East Prussia, devised his ophthalmoscope in 1850-51 in order to study the phenomenon of glowing eyes. With this instrument he was the first to see the retina of a living human. As means of illumination he used small panes of glass similar to cover-glasses which were introduced into the common visual axis of the observer and the subject at such an angle that light from a lamp was reflected into the subject's eye while the observer inspected the subject's retina through the glass and an appropriate lens. He recommended this type of illumination also for otoscopy. His invention was at once acclaimed throughout the world and opened completely new opportunities in ophthalmology. The slanting panes of glass, however, were not the ideal solution for illumination. It was only one year later that Ruete in Göttingen replaced them with a concave mirror with a central aperture, and there is every indication that Frank's report on Hofmann's mirror had suggested this technique to him. During the following two years quite a number of other modifications of the ophthalmoscope were constructed, all of them using the concave mirror with a central aperture, which soon became synonymous with the ophthalmoscope as such. Von Tröltsch, otologist and ophthalmologist in Würzburg, presented a concave mirror with a central aperture for otoscopy in Paris in 1855-56. His instrument was obviously derived from the already well known ophthalmoscope by adapting the diameter and focal distance to this special application. His primary concern was to use daylight instead of artificial light for otoscopy. Von Tröltsch did not know Hofmann's publication, but later did not hesitate to acknowledge Hofmann's priority. It was von Tröltsch who popularized the concave reflector with a central aperture as the instrument of choice in otoscopy, and subsequently also for rhinoscopy and laryngoscopy. Further modifications were devised to have the hands free for operations. Thus the reflector was fixed to the forehead by strap and buckle or a vulcanite band, or it was provided with a handle that was to be held between the teeth, or it was attached to a spectacle frame. The details of this interwoven history are related and highlighted by numerous quotations and historical illustrations.