Herman Snellen
Herman Snellen Sr (1834-1908) was a Dutch ophthalmologist
Snellen was a Dutch ophthalmologist whose name is synonymous with the Snellen chart, the universal tool for measuring visual acuity. Born in Zeist and trained at Utrecht University, Snellen joined the pioneering eye hospital led by Franciscus Donders, where he quickly became an authority on clinical ophthalmology. In 1862, he introduced a standardized system for vision testing using optotypes and the Snellen fraction (d/D), replacing inconsistent reading materials with precise, mathematically scaled letters. This innovation transformed eye care, education, and the evaluation of refractive errors worldwide.
Snellen’s contributions extended beyond visual testing. As Professor of Ophthalmology at Utrecht and later Director of the Netherlands Hospital for Eye Patients, he modernized surgical practice by promoting aseptic techniques, introducing cocaine anesthesia for ocular surgery, and refining procedures for conditions such as entropion, ectropion, and glaucoma. His surgical skill and systematic approach established the Dutch school of ophthalmology as a global leader in the field.
A prolific author and educator, Snellen collaborated with Donders and Landolt on landmark ophthalmic texts, presided over the International Ophthalmological Congress, and delivered the prestigious Bowman Lecture in London. His meticulous research and practical innovations bridged 19th-century ophthalmology and modern practice. Snellen died in 1908, leaving a legacy enshrined in every eye clinic worldwide, a line of letters that revolutionized the way we measure sight.
Biographical Timeline
- 1834 – Born February 19 in Zeist, Netherlands, son of physician Dr. F.A. Snellen.
- 1858 – Earned medical doctorate at Utrecht University, dissertation on the influence of nerves on inflammation. Appointed assistant physician at the Nederlandsch Gasthuis voor Ooglijders (Netherlands Hospital for Eye Patients) under Franciscus Donders (1818–1889).
- 1862 – Introduced the Snellen Chart, publishing Optotypi ad visum determinandum; pioneered use of optotypes and the Snellen fraction (d/D). Became primary physician at the Eye Hospital, managing patient care as Donders focused on physiology.
- 1874 – Co-authored major work on ophthalmic functional tests with Edmund Landolt in Graefe–Saemisch Handbuch der gesammten Augenheilkunde.
- 1877 – Appointed Professor of Ophthalmology at Utrecht University, becoming the first in the Netherlands to hold a chair dedicated to ophthalmology.
- 1884 – Succeeded Donders as Director of the Netherlands Hospital for Eye Patients; modernized surgical techniques and infrastructure.
- 1888 – Advocated aseptic techniques and introduced cocaine anaesthesia for ocular surgery.
- 1896 – Delivered the Bowman Lecture in London on vision and retinal perception.
- 1899 – Presided over the International Ophthalmological Congress in Utrecht; stepped down as professor the same year.
- 1903 – Retired as director of the Eye Hospital, succeeded by his son Herman Snellen Jr.
- 1908 – Died January 18 in Utrecht, aged 73; recognized globally for transforming visual acuity testing and operative ophthalmology.
Medical Eponyms
The Snellen Chart and Optotypes (1862)
Snellen’s greatest contribution was the creation of the Snellen chart, introduced in his 1862 publication Optotypi ad visum determinandum. Prior to this, visual acuity testing relied on arbitrary text, leading to inconsistent results.
The test for vision must rest on an objective standard, reproducible everywhere, so that the measure of visual power ceases to be arbitrary
The letters should be constructed on a square, and each part of the letter should be of uniform thickness and proportional length, so that its recognition depends solely upon the sharpness of the vision, and not upon its form or ornamentation.
Square letters whose limbs have a width equal to one fifth of the letters height are generally distinctly visible to a normal eye at an angle of five minutes.
Snellen standardized the process using optotypes—specially designed letters of uniform stroke width and proportion, each constructed within a 5 × 5 unit grid.
Snellen Fraction (1862)
Snellen introduced a formula to express visual acuity:
The formula for the acuteness of vision (v) is expressed by the utmost distance at which the types are recognized (d), divided by the distance at which they are seen at our standard angle of five minutes (D). The distances are taken by french metrical measure.
- v = acuteness of vision
- d = distance at which the test is performed (usually 6 m or 20 ft)
- D = distance at which a normal eye can read the letter
The Snellen fraction was more than a numerical convenience, it was a revolution in standardization. By scaling optotypes geometrically and defining acuity in terms of angular resolution (5 minutes of arc), Snellen linked clinical measurement to visual physiology. This approach underpins modern visual function research and international standards for acuity testing.
Thus, 6/6 (or 20/20) became the benchmark for normal vision. His chart remains the global standard for visual screening today.
Key Medical Contributions
Surgical Innovations and Clinical Practice
As Director of the Netherlands Hospital for Eye Patients and Professor at Utrecht, Snellen modernized ophthalmic surgery and set new standards for operative ophthalmology.
- Promoted aseptic technique in ocular procedures (1880s)
- Introduced cocaine anesthesia for eye surgery (1884), improving safety and comfort
- Refined operations for entropion, ectropion, glaucoma, and lacrimal disorders
- Advocated conservative approaches to cataract extraction and keratoplasty
Collaboration with Franciscus Donders
Snellen’s career was shaped by his close association with Franciscus Cornelis Donders (1818–1889), the physiologist who established Utrecht as a center of ophthalmic innovation. While Donders focused on optics and refraction, Snellen developed practical methods for visual testing and surgical care. Their partnership produced an internationally influential model of evidence-based ophthalmology, culminating in contributions to the Graefe–Saemisch Handbuch der gesammten Augenheilkunde (1874).
Legacy in Modern Ophthalmology
From rural clinics to space medicine, the Snellen chart remains the universal language of vision testing. Though later refinements (LogMAR, ETDRS charts) improved precision, Snellen’s principle endures as a simple, effective, and globally accessible tool. His work exemplifies the fusion of clinical utility, physiological insight, and design innovation, ensuring his name remains synonymous with visual acuity.
Major Publications
- Snellen H. De invloed der zenuwen op de ontsteking proefondervindelijk getoetst. [proefschrift] Utrechtsche Hoogeschool. Utrecht: P.W. van de Weijer; 1857.
- Snellen H. Probebuchstaben zur Bestimmung der Sehschärfe. 1862
- Snellen H. Optotypi ad visum determinandum. [English version: Test-types for the determination of the acuteness of vision ] 1862
- Snellen H. Letterproeven tot bepaling der gezichtsscherpte. Utrecht: J. Greven; 1862
- Snellen H, Landolt E. Ophthalmometrologie. Die Functionsprüfungen des Auges. In: Handbuch der gesammten Augenheilkunde [Eds Graefe A, Saemisch T. ] 1874
References
Biography
- Obituary: Herman Snellen, M.D. BMJ. 1908;I:295-6
- Koster W. Herman Snellen Sr. 19 februari 1834 – 18 januari 1908. Zijn beteekenis voor de ontwikkeling der oogheelkunde. Nederlands Tijdschrift voor Geneeskunde. 1908; 52: 282-9
Eponymous terms
- Küchler H. Schriftnummerprobe für Gesichtsleidende. Darmstadt: Diehl; 1843
- Linksz A. The development of visual standards: Snellen, Jaeger, and Giraud-Teulon. Bull N Y Acad Med. 1975 Feb;51(2):277-85.
- Keunen JE. De letterkaart volgens Snellen [Snellen’s letter chart]. Nederlands Tijdschrift voor Geneeskunde. 1986 Jan 25;130(4):173-6
- Brajkovich HL. Dr. Snellen’s 20/20: the development and use of the eye chart. J Sch Health. 1980 Oct;50(8):472-4
- Runge PE. Eduard Jaeger’s Test-Types (Schrift-Scalen) and the historical development of vision tests. Trans Am Ophthalmol Soc. 2000;98:375-438.
- van Gijn J, Gijselhart JP. Snellen en zijn optotypen [Snellen and his optotypes]. Nederlands Tijdschrift voor Geneeskunde. 2012;156(16):A4416.
- Azzam D, Ronquillo Y. Snellen Chart. 2023 May 1. In: StatPearls
- de Jong PTVM. A history of visual acuity testing and optotypes. Eye (Lond). 2024 Jan;38(1):13-24.
Eponym
the person behind the name
Physician in training. German translator and lover of medical history.
