Carl von Hess (7 March 1863, in

Mainz Mainz () is the capital and largest city of Rhineland-Palatinate, Germany. Mainz is on the left bank of the Rhine, opposite to the place that the Main (river), Main joins the Rhine. Downstream of the confluence, the Rhine flows to the north-we ...

– 28 June 1923, in Possenhofen) was a German

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 ...

known for his work in ocular physiology. He studied medicine at the universities of

Heidelberg Heidelberg (; Palatine German language, Palatine German: ''Heidlberg'') is a city in the States of Germany, German state of Baden-Württemberg, situated on the river Neckar in south-west Germany. As of the 2016 census, its population was 159,914 ...

Bonn The federal city of Bonn ( lat, Bonna) is a city on the banks of the Rhine in the German state of North Rhine-Westphalia, with a population of over 300,000. About south-southeast of Cologne, Bonn is in the southernmost part of the Rhine-Ruhr r ...

and

Strasbourg Strasbourg (, , ; german: Straßburg ; gsw, label=Bas Rhin Alsatian, Strossburi , gsw, label=Haut Rhin Alsatian, Strossburig ) is the prefecture and largest city of the Grand Est region of eastern France and the official seat of the Eu ...

, then traveled to

Prague Prague ( ; cs, Praha ; german: Prag, ; la, Praga) is the capital and largest city in the Czech Republic, and the historical capital of Bohemia. On the Vltava river, Prague is home to about 1.3 million people. The city has a temperate ...

, where he worked with ophthalmologist

Hubert Sattler Hubert Sattler (9 September 1844 – 15 November 1928) was an Austrian-German ophthalmologist born in Salzburg. His father, also named Hubert Sattler (1817–1904), and grandfather, Johann Michael Sattler (1786–1847), were both landscape pa ...

and physiologist

Ewald Hering Karl Ewald Konstantin Hering (5 August 1834 – 26 January 1918) was a German physiologist who did much research into color vision, binocular perception and eye movements. He proposed opponent color theory in 1892. Born in Alt-Gersdorf, Ki ...

. In 1891 he obtained his

habilitation Habilitation is the highest university degree, or the procedure by which it is achieved, in many European countries. The candidate fulfills a university's set criteria of excellence in research, teaching and further education, usually including a ...

from the

University of Leipzig Leipzig University (german: Universität Leipzig), in Leipzig in Saxony, Germany, is one of the world's oldest universities and the second-oldest university (by consecutive years of existence) in Germany. The university was founded on 2 Decemb ...

, and later on, he held professorships at the universities of

Marburg Marburg ( or ) is a university town in the German federal state (''Bundesland'') of Hesse, capital of the Marburg-Biedenkopf district (''Landkreis''). The town area spreads along the valley of the river Lahn and has a population of approximate ...

(from 1896),

Würzburg Würzburg (; Main-Franconian: ) is a city in the region of Franconia in the north of the German state of Bavaria. Würzburg is the administrative seat of the ''Regierungsbezirk'' Lower Franconia. It spans the banks of the Main River. Würzburg is ...

(from 1900) and

Munich Munich ( ; german: München ; bar, Minga ) is the capital and most populous city of the States of Germany, German state of Bavaria. With a population of 1,558,395 inhabitants as of 31 July 2020, it is the List of cities in Germany by popu ...

(from 1912).Hess, Carl von (bayerischer Personaladel 1912)
at

Neue Deutsche Biographie ''Neue Deutsche Biographie'' (''NDB''; literally ''New German Biography'') is a biographical reference work. It is the successor to the ''Allgemeine Deutsche Biographie'' (ADB, Universal German Biography). The 26 volumes published thus far cover ...

He made significant contributions in his studies of

refraction In physics, refraction is the redirection of a wave as it passes from one medium to another. The redirection can be caused by the wave's change in speed or by a change in the medium. Refraction of light is the most commonly observed phenomeno ...

and

accommodation of the eye Accommodation is the process by which the vertebrate eye changes optical power to maintain a clear image or focus on an object as its distance varies. In this, distances vary for individuals from the far point—the maximum distance from the eye ...

. He also conducted research on

color vision Color vision, a feature of visual perception, is an ability to perceive differences between light composed of different wavelengths (i.e., different spectral power distributions) independently of light intensity. Color perception is a part of ...

in the various retinal zones, on the various forms of

color blindness Color blindness or color vision deficiency (CVD) is the decreased ability to color vision, see color or differences in color. It can impair tasks such as selecting ripe fruit, choosing clothing, and reading traffic lights. Color blindness may ...

, of

simultaneous contrast A contrast effect is the enhancement or diminishment, relative to normal, of perception, cognition or related performance as a result of successive (immediately previous) or simultaneous exposure to a stimulus of lesser or greater value in the s ...

, on

afterimage AfterImage is a Filipino rock band formed in 1986, best known for their songs "Habang May Buhay", "Next in Line", and "Mangarap Ka". They disbanded in 1997 and became active again in 2008 after they reunited and released their fourth studio album ...

s of moving objects and of light-dark adaptation. In addition, he performed comparative physiological studies on light sense and color vision involving animals, in invertebrates as well as vertebrates. Along with Paul Römer, he made the discovery that

trachoma Trachoma is an infectious disease caused by bacterium ''Chlamydia trachomatis''. The infection causes a roughening of the inner surface of the eyelids. This roughening can lead to pain in the eyes, breakdown of the outer surface or cornea of ...

is transmissible to monkeys. His name is associated with the "Hess afterimage", defined as a positive afterimage that occurs third in the series of afterimages that are the result of exposure to a brief light stimulus (sequentially, the first afterimage is referred to as a "Hering afterimage", the second as a "Purkinje afterimage"). The Hess afterimage is defined as a physiological illusion. There are also several surgical instruments that are named after him.

Published works

* ''Die Refraktion und Akkommodation des menschlichen Auges und ihre Anomalien'', 1902 – Refraction and accommodation of the human eye and its anomalies. * ''Pathologie und Therapie des Linsensystems'', 1905 – Pathology and therapy 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''), ...

system. * ''Vergleichende Physiologie des Gesichtssinnes'', 1912 –

Comparative physiology Comparative physiology is a List of academic disciplines, subdiscipline of physiology that studies and exploits the diversity of functional characteristics of various kinds of organisms. It is closely related to evolutionary physiology and environ ...

of vision. * ''Die Entwicklung von Lichtsinn und Farbensinn in der Tierreihe'', 1914 – Development of light sense and color vision in the animal kingdom. He was also an editor of later editions of Saemisch and Graefe's "''Handbuch der gesamten Augenheilkunde''".Handbuch der gesamten Augenheilkunde
HathiTrust Digital Library

References

1863 births 1923 deaths Physicians from Mainz German ophthalmologists Academic staff of the University of Marburg Academic staff of the Ludwig Maximilian University of Munich Academic staff of the University of Würzburg {{Germany-bio-stub