Recently I rediscovered some articles for Eurotimes, the European Journal of Cataract and Refractive Surgeons that I had forgotten I had written. I have posted here before some of my book reviews for Eurotimes. I also wrote some pieces on historical ophthalmological figures – the first on Goethe and his work in optics, the second on Hermann von Helmholtz who was one of those towering, foundational figures in modern physics but who also invented the ophthalmoscope


In the last article, I considered one of the towering geniuses of world culture, Johann Wolfgang von Goethe. Goethe made enormous contributions to world literature and philosophy, and significant contributions to the nascent sciences of visual perception, linguistics, plant morphology, and felt he would be remembered most of all for his work on optics. Goethe perhaps epitomises the “natural philosopher”, the original term for “scientist” – an individual of boundless curiosity and enthusiasm, a gifted amateur in the true sense. Science owes much to the activities of men and women who operated outside the dynamic of universities and in an age before the research institute or the grant.

Hermann Ludwig Ferdinand von Helmholtz (1821-1894) is a less towering cultural presence than Goethe. His scientific activities have had a more lasting influence. He bridges the worlds of “natural philosophy” and organised, university based science – both in terms of his lifespan (eleven when Goethe died, he lived to directly influence Einstein and Maxwell) and in his professional life (originally training under paternal pressure as a doctor, he was appointed Professor of Physics in Berlin in 1871). Much of his work attacked the speculative tendencies of the natural philosophers, and was grounded firmly in observation and experiment.

Yet such was the breadth of his activity that he reminds one of the multi-talented natural philosopher as much as a contemporary, specialised physicist or physiologist. The Oxford Companion to the History of Modern Science describes him in summary as “physiologist, physicist, philosopher and statesman of science.” This begins to capture the breadth and diversity of his interest and involvement. We will discuss his work on perception, and on ophthalmic optics, below, but it is important to recall he was simultaneously working on conservation of energy, thermodynamics, and electrodynamics, and developed the philosophy of science itself. His writings ranged from the age of the earth to the origin and fate of the solar system.


One of the more humbling characteristics of the scientists of the past was their seeming mastery of measurement. We are so used to highly accurate, precise computerised measuring apparatus that we can forget that until relatively recently, researchers often had to build and calibrate their own equipment. And going back only a little further, they had to invent it as well. Most readers of EuroTimes probably use one of Helmholtz’s inventions every day – the ophthalmoscope.

Invented in 1851, the ophthalmoscope is a perfect illustration of Helmholtz’s combination of experimental and inventive skill. The invention made him world famous overnight. Helmholtz was actually independently reinventing a device of Charles Babbage’s from 1847. As so often in science, it was the reinventor who recognised the usefulness and applicability of the invention, rather than the first inventor (Babbage, of course, also managed to invent but not complete the first computer) The handheld ophthalmoscope was developed by Greek ophthalmolosist Andreas Anagonstakis later in the 1850s, and in 1915 William Noah Allyn and Frederick Welch invented the self illuminating ophthalmoscope (and founded Welch Allyn) that is the direct precursor of the modern device.

Who was Helmholtz, this man of so many talents and interests and such lasting influence? Born in Potsdam on 31st August 1821 into a lower middle class family that emphasised the importance of education and cultural activities, his father Ferdinand was a teacher of philosophy and psychology in the local secondary school. His mother was a descendant of William Penn, the founder of Pennsylvania, and her maiden name was Penne. Ferdinand Helmholtz was also a close friend of the philosopher Fichte. The scientific and philosophical worlds of the nineteenth century often seem amazingly small and parochial.


Helmholtz’s natural inclination as a student was to pursue studies in physics – however his father observed the financial support available for medical students and the lack thereof for physics students, and persuaded him into medical studies. He enrolled in the Friedrich-Wilhelms-Institut in Berlin, the Prussian military’s medical training college. After this, the served as a medical officer in the Prussian military for a time, simultaneously publishing articles on heat and muscle physiology. In 1847 he published his treatise On The Conservation of Force, which was the clearest and ultimately most influential account of what would become known as the principle of the conservation of energy. From his observations of muscles physiology and activity, he tried to demonstrate that there is no energy loss in muscle movement, and no “life force” is necessary to move a muscle.

In 1848 he left military service and embarked on an academic career. In 1849, he became an associate professor of physiology in Konigsberg.. Shortly after he announced the invention of the ophthalmoscope and also made another discovery that would seal his fame – measuring the rate of conduction of signals in nerves. It had been believed that sensory signals arrived at the brain instantaneously, and it was considered beyond the capabilities of experimental science to measure the rate of nerve conduction. Using a new invention, the chronograph, Helmholtz measured the difference between stimulus and reaction times at different parts of the body, and found the speed of neural conduction to be comparable to that of sound, not light.

A full account of all Helmholtz’s discoveries and scientific achievements would take volumes. He had an intense interest in visual perception, especially visual illusions. This interest was based on his philosophical position that we are separate from the world of objects, and isolated from external physical events, except for perceptual signals which, not unlike language, must be learned and read according to various assumptions. These assumptions may or may not be appropriate. This philosophy underlay many of his research activities and interests, and also his idea that perceptions are “unconscious inferences.”

Most of what goes on in the nervous system, according to Helmholtz, is not represented in consciousness. Psychological and physiological experimental findings often surprise us for this reason, because we cannot discover by introspection how we see or how we think. We derive a perception from incomplete data, hence “unconscious inference.” This idea influenced Freud’s idea of the unconscious, and Helmholtz’s student Wilhelm Wundt, who took Helmholtz’s work and ideas further. Another of his students, Heinrich Hertz, further developed Helmholtz’s work on energy and electrodynamics.

Helmholtz had a huge impact on all areas of perceptual science, and many areas of physics. His name lives in a variety of laws and concepts (Helmholtz illusion, Helmholtz free energy, Helmholtz-Kelvin contaction) and that of an association of research institutes in Germany. And of course, for the humble working ophthalmologist, every day, almost without thinking, Helmholtz’s influence as the originator of the modern ophthalmoscope is literally palpable.


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