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The Snellen Eye Chart: A Quick History

Phoebe Jade

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Phoebe Jade

Updated: 18 April 2024 •  
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Have you ever heard of the Snellen eye chart? You might recognize it as the chart with the big E at the top that you see at the optometrist’s office. But did you know there’s much more to this chart than identifying letters?
In this article, we’ll explore the fascinating history of the Snellen eye chart and how it works. We will also discuss its use and what it can tell us about our vision.

What is the Snellen eye chart?

The Snellen eye chart helps measure visual acuity, which is how well a person can see at specific distances.
The chart displays 11 rows of letters that decrease in size as you move down the chart. To take the test, you stand a specific distance from the chart and read the row of letters out loud. The smallest row you can read accurately determines your visual acuity.
a snellen eye chart hung on the wall

The Snellen eye chart displays 11 rows of letters that decrease in size as you move down the chart.

Optometrists, ophthalmologists, and other medical professionals commonly use this simple eye chart to diagnose and manage vision issues such as nearsightedness, farsightedness, and astigmatism.
The Snellen eye chart also helps schools, universities, and some employers to evaluate an individual’s ability to see clearly.
Snellen eye charts are found in many optical shops, ophthalmology clinics, and some doctor’s offices. If you’ve ever taken a driver’s license test, you’ve encountered the chart.
The Snellen chart is quite common, but it actually has other variations.

Bailey-Lovie chart

Australian optometrists Bailey and Lovie improved upon the Snellen chart, as they recognized some issues with it. They created a new chart in 1976 called the Bailey-Lovie chart. This new eye chart is made up of 14 rows, with five letters each, decreasing in size from top to bottom.

ETDRS chart

In 1982, Rick Ferris developed the ETDRS chart by modifying the Bailey-Lovie chart to address the Snellen chart’s limitations. The ETDRS tests from 13 feet, with each row containing the same number of letters – five, and equal spacing of letters and rows.

The origin of the Snellen eye chart

The Snellen eye chart can trace its roots back to Herman Snellen, a Dutch ophthalmologist who lived in the mid-1800s. Snellen was a student of Cornelius Donders, another famous Dutch ophthalmologist who was instrumental in developing the field of visual perception.
Snellen created the eye chart in 1862 as part of his research on visual acuity. He aimed to develop a test that was both standardized and easy to administer. The chart he created consisted of letters of different sizes arranged in rows.
portrait of herman snellen and the snellen eye chart

Herman Snellen, a Dutch ophthalmologist, created the eye chart in 1862 as part of his research on visual acuity. Source: Twitter

It significantly improved over previous tests, which tended to be inconsistent and subjective. Snellen’s chart quickly gained popularity and became the standard method for testing visual acuity in the Netherlands and worldwide.
Today, the Snellen eye chart remains one of the most recognized and valuable tools in ophthalmology.

The Snellen fraction helps define visual acuity

Aside from being the most recognizable eye chart, the Snellen is also the origin of the well-known “20/20” measurement for visual acuity.
This fraction refers to the letters on the fourth line of the Snellen chart, which correspond to what a person is expected to see with normal, healthy vision at a distance of 20 feet.
If a person can read that line at 20 feet, they are said to have 20/20 vision. A person with 20/40 vision can read at 20 feet, while a person with normal vision can read at 40 feet.
Interestingly, outside the United States, visual acuity is measured in meters, with normal vision expressed as 6/6 (meters). This notation, used in many countries worldwide, is similar to the 20/20 measurement in the USA.
The standardization of visual acuity measurement has helped identify many eye conditions at an early stage and is a crucial step in maintaining optimal eye health.

How to use the Snellen eye chart at home

Although the Snellen eye chart is commonly used in eye doctor’s offices, it’s possible to use it at home to test your vision.
woman using snellen eye chart at home

Using the Snellen eye chart at home to test your vision is possible.

To do so, hang the chart on a wall at eye level, ensuring plenty of light in the room. Stand 20 feet away. Cover one eye, and read out the letters on the chart. Then, repeat this process with the other eye.
This is especially useful for parents who want to test their children’s vision for signs of nearsightedness. Also, it can be a helpful tool in self-assessing whether you meet the legal visual acuity requirements for obtaining a driver’s license.
However, it’s important to note that regular eye exams with a certified ophthalmologist are still recommended for the most accurate results and prescriptions.

Alternatives to the Snellen eye chart

The Snellen chart may be the most recognizable, but eye doctors also use other eye charts to check visual acuity.

Tumbling E chart

tumbling E chart

The Tumbling E chart aids children and individuals unfamiliar with the Roman alphabet. Source: DB Occupational Health LTD

Dr. Snellen, the inventor of the Snellen chart, also created the Tumbling E chart. This eye chart was intended for children and individuals who can’t read or don’t know the Roman alphabet. On this chart, the capital letter E faces different directions. The patient needs to point the direction the letter is facing.

LEA symbols chart

LEA symbols chart

The LEA Symbols Chart helps overcome language barriers in visual acuity tests for children. Source: ResearchGate

Created to overcome language barriers in visual acuity tests in children, the LEA Symbols Chart uses symbols instead of letters, creating a fun environment for kids during their eye exams.

Jaeger chart

jaeger chart for vision test

The Jaeger chart helps test near vision and consists of 11 numbered paragraphs. Source: Medisave

The Jaeger chart was created in 1854 by an Austrian ophthalmologist named Jaeger. It’s used to test near vision and consists of 11 numbered paragraphs, each with different font sizes. While testing, the card is about 14 inches away from the nose (typically at a distance that is comfortable for reading).

The Snellen eye chart: a common & useful tool for testing visual acuity

Herman Snellen’s first eye chart has come a long way since its invention in the mid-1800s. Over the years, many other eye charts have emerged that bring unique strengths and purposes.
Today, eye care and technology advancements have enabled ophthalmologists to diagnose and treat eye conditions with great precision. Undoubtedly, the Snellen chart remains an essential tool in eye care, ensuring accurate and consistent measurement of visual acuity.

Phoebe Jade

Written by:

Phoebe Jade

Phoebe is a registered nurse, licensed teacher and writer who's passionate about creating content that educates and inspires.