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Dutch master Herman Snellen famous for visual acuity testing chart

Andrzej Grzybowski

Posted: Tuesday, November 1, 2016

There are few names in ophthalmology better known than Herman Snellen, mostly because of his work on visual acuity testing and the chart he introduced for this purpose. Snellen was born in Zeist, near Utrecht, The Netherlands in 1834. He was the son of the popular physician Dr F A Snellen. In Utrecht, he studied medicine and received his medical doctorate in 1858 based on his work on “Experimental examination about the influence of the nerves on the inflammation”.

In the same year, he received a position as assistant physician in the ophthalmological clinic ‘Nederlandsch Gasthuis voor Ooglijders’, founded by his teacher and mentor Franz Cornelius Donders. In 1862 he became primary physician, and in 1884 director of the institution. During the first 10 years of institute work, 12,592 out- and 3,130 in-patients were treated and 2,885 operations were performed.
The clinic’s history is closely connected with the modern history of Dutch ophthalmology. It was a training centre for Dutch as well as foreign physicians, and numerous theses and publications originated there.

VISUAL ACUITY TESTING
Snellen was the first assistant professor in The Netherlands who dedicated himself entirely to ophthalmology. In 1877, he became Professor of Ophthalmology at Utrecht University.
He had 12 children, and was succeeded by Herman Snellen Jr. Snellen left behind comprehensive work on many topics including anterior synechiae, astigmatism, accommodation, keratoconus, defective colour vision, amaurotic eyes, sympathetic ophthalmia, inflammation, diseases of the retina and connective tissue, eyeball prosthesis, the history of glaucoma treatment and eye examinations.

He is, however, best remembered today due to his improvements of eyelid operations, including ectropion, entropion and trichiasis (tarsal wedge resection) and his work on visual acuity testing.

In 1862 he published his work Test-types for the determination of the acuteness of vision, in which he described in detail his concept: “Over each series of letters of the same size a number was placed indicating the distance (in feet or metres) at which the letters subtended an angle of five minutes. In calculating the size, the arc and not the tangent was taken. The degree of acuteness of vision (V) is expressed by the relation of the distance at which the letter is actually seen (d), to that at which the letter is apparent at an angle of five minutes (D); V= d/D.”

Herman Snellen

Herman Snellen

Snellen was not the first or last person to create test charts. The first known was Benito Daça de Valdes (1591–1634), who in 1623 proposed to present small objects of regular size and determine the distance at which they could not be discerned, and who measured the distance at which a row of mustard seeds could not be counted. He also varied the distance at which small print could be read.
In 1843, Heinrich Georg Küchler (1811–1873), a German ophthalmologist from Darmstadt, invented a chart consisting of figures of various objects (birds, frogs, farm implements, cannons etc.) cut from calendars and almanacs, which he glued to a sheet of paper in decreasing size.

FIXED DISTANCE
Eduard Jäger von Jaxtthal (1818–1884), an Austrian ophthalmologist, in 1854 made improvements to eye chart test types that were earlier developed by Küchler for testing near vision acuity. He introduced a card 
on which paragraphs of text were printed, with the text sizes increasing from 0.37mm to 2.5mm. The card was to be held by a patient at a fixed distance and the smallest print that the patient could read determined their visual acuity.

Among Snellen’s innovations were the following:
l Rather than using existing typefaces, he designed special characters, which he called optotypes, for the specific purpose of visual acuity measurement.

l He arranged these optotypes in a letter chart format to be used as a test of distance vision.
l He calibrated his characters based on an external standard (5’ arc), so that others who wanted to reproduce them or design their own, could calibrate them to the same standard.
l He popularised his charts in different languages.

Although Dutch ophthalmology has had many recognised experts and important achievements, so far no one has been able to contribute more to world ophthalmology than Donders and Snellen.

Andrzej Grzybowski MD, PhD is Professor of Ophthalmology, Poznan-Olsztyn, Poland

There are few names in ophthalmology better known than Herman Snellen, mostly because of his work on visual acuity testing and the chart he introduced for this purpose. Snellen was born in Zeist, near Utrecht, The Netherlands in 1834. He was the son of the popular physician Dr F A Snellen. In Utrecht, he studied medicine and received his medical doctorate in 1858 based on his work on “Experimental examination about the influence of the nerves on the inflammation”.

In the same year, he received a position as assistant physician in the ophthalmological clinic ‘Nederlandsch Gasthuis voor Ooglijders’, founded by his teacher and mentor Franz Cornelius Donders. In 1862 he became primary physician, and in 1884 director of the institution. During the first 10 years of institute work, 12,592 out- and 3,130 in-patients were treated and 2,885 operations were performed.
The clinic’s history is closely connected with the modern history of Dutch ophthalmology. It was a training centre for Dutch as well as foreign physicians, and numerous theses and publications originated there.

VISUAL ACUITY TESTING
Snellen was the first assistant professor in The Netherlands who dedicated himself entirely to ophthalmology. In 1877, he became Professor of Ophthalmology at Utrecht University.
He had 12 children, and was succeeded by Herman Snellen Jr. Snellen left behind comprehensive work on many topics including anterior synechiae, astigmatism, accommodation, keratoconus, defective colour vision, amaurotic eyes, sympathetic ophthalmia, inflammation, diseases of the retina and connective tissue, eyeball prosthesis, the history of glaucoma treatment and eye examinations.
He is, however, best remembered today due to his improvements of eyelid operations, including ectropion, entropion and trichiasis (tarsal wedge resection) and his work on visual acuity testing.

In 1862 he published his work Test-types for the determination of the acuteness of vision, in which he described in detail his concept: “Over each series of letters of the same size a number was placed indicating the distance (in feet or metres) at which the letters subtended an angle of five minutes. In calculating the size, the arc and not the tangent was taken. The degree of acuteness of vision (V) is expressed by the relation of the distance at which the letter is actually seen (d), to that at which the letter is apparent at an angle of five minutes (D); V= d/D.”

Snellen was not the first or last person to create test charts. The first known was Benito Daça de Valdes (1591–1634), who in 1623 proposed to present small objects of regular size and determine the distance at which they could not be discerned, and who measured the distance at which a row of mustard seeds could not be counted. He also varied the distance at which small print could be read.

In 1843, Heinrich Georg Küchler (1811–1873), a German ophthalmologist from Darmstadt, invented a chart consisting of figures of various objects (birds, frogs, farm implements, cannons etc.) cut from calendars and almanacs, which he glued to a sheet of paper in decreasing size.

FIXED DISTANCE
Eduard Jäger von Jaxtthal (1818–1884), an Austrian ophthalmologist, in 1854 made improvements to eye chart test types that were earlier developed by Küchler for testing near vision acuity. He introduced a card 
on which paragraphs of text were printed, with the text sizes increasing from 0.37mm to 2.5mm. The card was to be held by a patient at a fixed distance and the smallest print that the patient could read determined their visual acuity.
Among Snellen’s innovations were the following:
* Rather than using existing typefaces, he designed special characters, which he called optotypes, for the specific purpose of visual acuity measurement.

* He arranged these optotypes in a letter chart format to be used as a test of distance vision.
* He calibrated his characters based on an external standard (5’ arc), so that others who wanted to reproduce them or design their own, could calibrate them to the same standard.
* He popularised his charts in different languages.

Although Dutch ophthalmology has had many recognised experts and important achievements, so far no one has been able to contribute more to world ophthalmology than Donders and Snellen.

Although Dutch ophthalmology has had many recognised experts and important achievements, so far no one has been able to contribute more to world ophthalmology than Donders and Snellen.

Andrzej Grzybowski MD, PhD is Professor of Ophthalmology, Poznan-Olsztyn, Poland