• Vision

Eighteen hundred and fifty-one, the year in which Hermann von Helmholtz introduced his ophthalmoscope, can be regarded as the dawn of modern ophthalmology. A decade later, the binocular form of this instrument appeared on the scene. Invented by Marc-Antoine Giraud-Teulon (1816–1887; figure 1) the first model was made by Nachet of Paris and consisted of two solid rhomboid prisms placed in a metal carrier with a perforated concave mirror mounted on the front of the instrument. The instrument was hand-held with the other hand holding a condensing lens to form the virtual, reversed image for the indirect method of ophthalmoscopy. Illumination, directed via the concave mirror into the patient's eye, was from an oil lamp positioned above the patient's head.

The instrument was difficult to use, because of the low level of illumination and in this first model, the fixed inter-pupillary distance setting. The latter problem was solved in Giraud-Teulon's second model in which the right hand prism was divided, the end section moving in and out with a handle on a screw thread thus providing a range of inter-pupillary settings. A sliding mechanism provided prisms behind the eyepieces to aid fusion. In 1862 John Zachariah Laurence, founder of the South London Ophthalmic Hospital, joined up with Charles Heisch to produce a more sophisticated instrument with variable inter-pupillary and vergence adjustments.

Despite the endorsement of Professor Hermann Knapp, these binocular ophthalmoscopes did not prove popular. Lack of adequate illumination, difficulty in co-ordinating the angle of illumination, binocularity and maintaining the patient's fixation were too tedious difficulties for most practitioners to surmount. Besides, these were early …