Marius Hans Erik Tscherning (11 December 1854, in Østrup near

Odense Odense ( , , ) is the third largest city in Denmark (behind Copenhagen and Aarhus) and the largest city on the island of Funen. As of 1 January 2022, the city proper had a population of 180,863 while Odense Municipality had a population of 20 ...

– 1 September 1939) was a

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ophthalmologist Ophthalmology ( ) is a surgery, surgical subspecialty within medicine that deals with the diagnosis and treatment of eye disorders. An ophthalmologist is a physician who undergoes subspecialty training in medical and surgical eye care. Followin ...

. Tscherning first studied with

Peter Ludvig Panum Peter Ludvig Panum (19 December 1820 – 2 May 1885) was a Danish physiologist and pathologist born on the island of Bornholm in Rønne. The Panum Institute in Copenhagen is named in his honor. Early life and education Panum was born in Rønn ...

.O’Shea, R. P., Roeber, U., & Wade, N. J. (2017). On the discovery of monocular rivalry by Tscherning in 1898: Translation and review. i-Perception, 8(6), 1-12. https://doi.org/10.1177/2041669517743523 Then he studied ophthalmology under Edmund Hansen Grut (1831–1907) in

Copenhagen Copenhagen ( or .; da, København ) is the capital and most populous city of Denmark, with a proper population of around 815.000 in the last quarter of 2022; and some 1.370,000 in the urban area; and the wider Copenhagen metropolitan ar ...

. Later Tscherning became an adjunct director at the ophthalmological laboratory at the

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Paris Paris () is the capital and most populous city of France, with an estimated population of 2,165,423 residents in 2019 in an area of more than 105 km² (41 sq mi), making it the 30th most densely populated city in the world in 2020. S ...

. Tscherning spent 25 years at the Sorbonne, where he worked closely with Louis Émile Javal (1839–1907). In 1910 he returned to Denmark as a professor at the

University of Copenhagen The University of Copenhagen ( da, Københavns Universitet, KU) is a prestigious public university, public research university in Copenhagen, Copenhagen, Denmark. Founded in 1479, the University of Copenhagen is the second-oldest university in ...

and head of the ophthalmic department at the

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.Salmonsens konversationsleksikon
(biography) Tscherning is remembered for contributions made in optical

physiology Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemical ...

. He conducted research of

entoptic phenomenon Entoptic phenomena () are visual effects whose source is within the human eye itself. (Occasionally, these are called entopic phenomena, which is probably a typographical mistake.) In Helmholtz's words: "Under suitable conditions light falling o ...

Purkinje images Purkinje images are reflections of objects from the structure of the eye. They are also known as Purkinje reflexes and as Purkinje–Sanson images. At least four Purkinje images are usually visible. The first Purkinje image (P1) is the reflectio ...

, the

etiology Etiology (pronounced ; alternatively: aetiology or ætiology) is the study of causation or origination. The word is derived from the Greek (''aitiología'') "giving a reason for" (, ''aitía'', "cause"); and ('' -logía''). More completely, e ...

myopia Near-sightedness, also known as myopia and short-sightedness, is an eye disease where light focuses in front of, instead of on, the retina. As a result, distant objects appear blurry while close objects appear normal. Other symptoms may include ...

, and

Listing's law Listing's law, named after German mathematician Johann Benedict Listing (1808–1882), describes the three-dimensional orientation of the eye and its axes of rotation. Listing's law has been shown to hold when the head is stationary and upright and ...

of ocular movement. He discovered the phenomenon of

monocular rivalry Monocular rivalry is a phenomenon of human visual perception that occurs when two different images are optically superimposed. During prolonged viewing, one image becomes clearer than the other for a few moments, then the other image becomes clear ...

in which two superimposed images fluctuate in clarity or visibility. He also designed an ophthalmophacometer, a device used to measure changes that happen in the front and back curvatures of the

lens A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements''), ...

during accommodation. He is probably best known for his theory regarding the mechanism of accommodation, of which he disagreed with the accommodation theory proposed by

Hermann von Helmholtz Hermann Ludwig Ferdinand von Helmholtz (31 August 1821 – 8 September 1894) was a German physicist and physician who made significant contributions in several scientific fields, particularly hydrodynamic stability. The Helmholtz Association, ...

(1821–1894). Tscherning believed that accommodation occurred through an increase of zonular pressure at the lens equator with contraction of the

ciliary muscle The ciliary muscle is an intrinsic muscle of the eye formed as a ring of smooth muscleSchachar, Ronald A. (2012). "Anatomy and Physiology." (Chapter 4) . in the eye's middle layer, uvea ( vascular layer). It controls accommodation for viewing ...

, and therefore a bulging of the lens in accommodation was created by compression rather than by passive dilatation. Furthermore, he stated that during accommodation, while the central part of the anterior surface of the lens is bulged, the peripheral portion of the lens is flattened. Tscherning was the author of over 100 scientific articles, including a book titled ''Optique physiologique'', published in 1898 in

by Garré and Naud, and was later translated into English
''Physiologic optics''
, and ''Hermann von Helmholtz et la Théorie de l´Accommodation'', Paris 1909 Octave Doin, ("Hermann von Helmholtz and the Theory of Accommodation") which was critical to Helmholtz's work on the same subject, published in the Graefe's Archiv (volume 1, 1854). In 1894 he published ''Œvres ophthalmologiques de Thomas Young'' ("Ophthalmological oeuvres of Thomas Young").

Associated eponym

* "Tscherning's ellipse": A term used in

corrective lens A corrective lens is a lens (i.e. a transmissive optical device) that is typically worn in front of the eye to improve daily vision. The most common use is to treat refractive errors: myopia, hypermetropia, astigmatism, and presbyopia. Glass ...

design. A graphical representation of the front surface power as a function of total

lens power In optics, optical power (also referred to as dioptric power, refractive power, focusing power, or convergence power) is the degree to which a lens, mirror, or other optical system converges or diverges light. It is equal to the reciprocal of the ...

in best-form lenses.Medical Dictionary
Tscherning ellipse

References

* ttp://www.iovs.org/cgi/content/full/47/1/278 Accommodative Changes in Lens Diameter* Julius Hirschberg/History of Ophthalmology, volume 11/part 1a, Wayenborgh, Bonn 1992, p. 173, * Albert, Norton & Hurtes "Source Book of Ophthalmology" Blackwell Science 1995, {{DEFAULTSORT:Tscherning, Marius Danish ophthalmologists 1854 births 1939 deaths Academic staff of the University of Paris