Snellen board - a small piece of paper that revolutionized vision diagnostics
Have you ever wondered where the well-known board with letters of different sizes that we see during eye examinations came from? This inconspicuous piece of paper, known as the Snellen chart, played a key role in the development of ophthalmic diagnosis and is still used today - not only in ophthalmologists' offices, but also in screening or occupational medicine.
A brief look back - the history of the plaque
The Snellen chart was created in 1862 by Dutch ophthalmologist Hermann Snellen. He worked at an eye clinic in Utrecht, where he attempted to create a universal method of assessing visual acuity.
Earlier attempts to diagnose vision problems had been rather unsystematic - there were no uniform standards or tools. Snellen designed his chart so that each line consisted of letters of a precise size and shape, with each successive line containing characters smaller than the previous one.
Snellen did not use ordinary fonts - he developed special characters, called optotypes, in which each letter was constructed according to mathematical rules - its elements were proportional to the total height of the character.
How does the Snellen array work?
During the test, the patient stands (or sits) at a distance of 6 meters (or 20 feet) from the board. The largest letter at the top should be visible to a person with normal vision from just this distance. Subsequent lines contain smaller and smaller letters, which correspond to different levels of visual acuity.
The test result is recorded as a fraction, such as 6/6 (or 20/20 in imperial units), which indicates normal vision. A result of 6/12, on the other hand, suggests that the patient sees from 6 meters what a person with normal vision sees from 12 meters.
Practical application
The Snellen chart is one of the most widely used tools in ophthalmology and optometry. It is used in, among other things:
- Basic ophthalmic examinations
- Driver's license issuance and renewal
- Occupational medicine
- Screening in schools and workplaces
- Diagnosis and monitoring of refractive errors, such as nearsightedness or farsightedness
Interestingly, there are also many specialized versions, such as for children (with symbols instead of letters), illiterate people, or patients with very low visual acuity.
Modern interpretations
While the classic Snellen chart is still the standard in many offices, technology is increasingly entering the scene. Mobile apps, interactive vision tests and even virtual reality offer modern versions of visual acuity tests, but - interestingly - they are still based on Snellen's concept from more than 160 years ago.
What can we learn from this?
The Snellen chart is a beautiful example of how simple solutions, based on a deep understanding of the patient's needs, can stand the test of time. Today, in the age of innovation and advanced diagnostics, it is worth remembering that sometimes the most effective tools are.... analog.
