We were fortunate enough to acquire this ophthalmometer together with around 1000 other objects from the former Institute of Physics for the collection of scientific instruments and teaching aids. Many of these objects come from lecture experiments, the Department of Industrial Research (AFIF) and optical research. This also includes the ophthalmometer.
Hermann von Helmholtz – physiologist, physician and physicist
The ophthalmometer was invented by Hermann von Helmholtz (1821-1894) in 1850. In the field of optics and ophthalmology, Helmholtz is considered one of the most important scientists of the 19th century. He is described as a pioneer, if not one of the last universal geniuses, and is considered a visionary of modernity in the fields of sensory physiology, acoustics, colour perception and physiological optics. 1
Helmholtz studied medicine and received his doctorate in microscopic anatomy in 1842, at the age of 21. Medicine was never his preferred field of study; he became increasingly interested in physics and also worked in this field. After holding several chairs in physiology, he held the chair of physics at Berlin’s Friedrich Wilhelm University from 1870.2
Helmholtz belonged to various scholars’ societies and academies and was well connected in the scientific world; with individuals such as Alexander von Humboldt and Robert von Bunsen – inventor of the Bunsen burner. Helmholtz took over as director of Berlin’s Physikalische-Technische Reichsanstalt, forerunner of today’s Physikalisch-Technische Bundesanstalt, in 1887. Helmholtz died in Berlin in 1894 at the age of 73. His life’s work includes around 220 publications.3
The ophthalmometer
In his Handbuch der physiologischen Optik [Manual of Physiological Optics], Helmholtz describes the ophthalmometer he developed in 1850 as follows: “The ophthalmometer is essentially a telescope which is equipped for seeing at short distances […]”4. This instrument measures the curvature of the cornea of the eye. If the shape of the cornea is irregular, this can lead to vision problems. The person being examined looks into a kind of cube containing two plane-parallel glass plates that are rotated around a common axis. This can be seen in the 3D model by selecting the “Mechanics” section in the animation.
in: Meyers Großes Konversations-Lexikon, Band 2. Leipzig 1905.
The functioning of the ophthalmometer is described in the “Meyers Grosses Konversations-Lexikon” encyclopaedia as follows:
«If the plates are perpendicular to the axis, they are in the zero position (g1g1). The plates can be moved through equal angles in opposite directions by means of a gear. The angle size can be read off a vernier. Through the telescope (R), the observer (B) sees the two reflex images of two flames 1 and 2 on the cornea of the person being examined (A), who is looking towards F. If the glass plates are in the zero position, they have no influence on the reflected images. But if they cross at any angle, half of the rays are shifted to one side, the other half to the other: each of the flames then appears in duplicate. If we now shift the plates so far to the side that the middle images of the four coincide, you can calculate the distances of the reflected images from 1 and 2 from the read angle of rotation. We have thus found the size of the image of lens 1–2 and can also calculate the radius of curvature of the cornea using this formula.»
Augenkrankheiten, Augenuntersuchungen, in: Meyers Großes Konversations-Lexikon, Volume 2. Leipzig 1905.
At the time when the ophthalmometer was invented in 1850, Helmholtz was full professor of physiology in Königsberg. This invention stems from his wish to illustrate the glow of cat’s eyes to his students using an “ophthalmoscope”, i.e. the ophthalmometer. This instrument soon became very important to practising ophthalmologists for diagnostics, as well as bringing renown to Helmholtz.5
Nowadays, the radius of curvature of the cornea is measured using a keratometer, which is a direct successor of the ophthalmometer. By inventing the ophthalmometer, Helmholtz ushered in a new era in ophthalmology.
Moritz Meyerstein, manufacturer
Moritz Meyerstein (1808-1882), a manufacturer, was also part of Helmholtz’s network of scholars. This German mechanic held the role of University Instrument and Machine Inspector in Göttingen starting from 1841. In this capacity, he worked with renowned scientists such as Carl Friedrich Gauss, Wilhelm Eduard Weber and Robert Bunsen. Helmholtz, too, was convinced of Meyerstein’s abilities and commissioned him to manufacture his ophthalmometer.
3D Digitalisation
Object selection
The ophthalmometer is an object that exemplifies the rapid development of science that occurred in the 19th century. As a pioneering instrument for the development of ophthalmology, it still has an impact today. Only a few collections and museums possess a Meyerstein / Helmholtz ophthalmometer. Thanks to 3D digitisation, our instrument is accessible for research and teaching from any location.
For conservation reasons, the ophthalmometer can only be viewed from the outside if exhibited or shown as part of a guided tour. The 3D model, on the other hand, affords viewers a close look inside the cube-shaped box which holds the two mirrors and thus the instrument’s actual measuring apparatus. The movement of the mirror plates and thus how the instrument works can be easily understood through the animation.
Photogrammetry and modelling
The animations and the entire mechanics with the two glass surfaces inside the measuring cube were created fully by hand. The components of the original object were measured to ensure that the digital copy matches the original.