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Ever thought about taking an eye test? Take it here!

Vojtěch Brtinský

Medically reviewed by Vojtěch Brtinský, Optometrist, on 29 Jan 2021
Written by Leonie Bauer

The World Health Organization revealed new figures for vision impairment in October 2018. Globally, it is estimated that approximately 1.3 billion people live with some form of vision impairment. Regarding distance vision, 188 million people have mild vision impairment, 217 million have moderate to severe vision impairment, and 36 million people are blind. (World Health Organization)

Vision impairment worldwide

All these people need some kind of visual aid, typically contact lenses or glasses, to improve their vision. But how do you find out if you need such visual aids? How do you measure your eyesight?

Monoyer's Eye Chart

Monoyer Eye Chart In order to test your eyesight, you need to take an eye test. The inventor of the first decimal eye test was Ferdinand Monoyer. The French ophthalmologist created his famous Monoyer Eye Chart in 1872 and provided a unit of measurement for the optical power of a lens, called a dioptre. Each row of letters in different sizes represents a different dioptre – the unit that is still in use today.

A dioptre is a unit of measurement of the optical power of a lens or curved mirror, which is equal to the reciprocal of the focal length measured in metres (that is, 1/metres). It is thus a unit of reciprocal length. For example, a 3-dioptre lens brings parallel rays of light to focus at 1⁄3 metre. Optical power of the human eye is 58 D.

Fun fact: Monoyer also inserted his name into the chart. Reading upwards, ignoring the last line, the letters on the left-hand side spell ‘Monoyer’, the letters on the right-hand side ‘Ferdinand’. Can you spot it? (Independent)

What about the Snellen Eye Chart?

Soon after Monoyer published his eye test, the Dutch eye doctor Herman Snellen developed a similar chart, the Snellen Eye Chart. The first version used abstract symbols, which were then replaced with letters. Unlike the previous model, it placed the largest letters at the top. 

The chart consists of 11 lines of block letters, beginning with big letters on the top row. The size of the letters progressively decreases, allowing for more letters on each subsequent line. (Very Well Health)

The Snellen Chart is still used today to measure people’s eyes. During an eye exam the eye doctor will ask you to find the smallest line of text letters that you can make out, and ask you to read it. If you can read the bottom row of letters, your visual acuity is very good.



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Take an eye test here

If you want to find out whether you need glasses or contact lenses, book an eye test with your local eye care practitioner. Before you visit your doctor or optician, you can do the Snellen Eye Test at home.

The test we're providing here can be useful to test nearsightedness, which causes blurry distance vision. That is particularly helpful to screen children for nearsightedness.

Farsightedness, astigmatism, or other eye problems can't be measured with our chart. Only a comprehensive eye examination by a licensed eye specialist or ophthalmologist can determine whether your eyes are healthy and you can see as clearly and comfortably as possible.

How to use our online Snellen Eye Chart

For the best accuracy, have someone assist you when testing your vision with the Snellen Eye Chart.

  • Place the chart on a wall about three metres away.
  • Cover one eye and read aloud the letters on the chart.
  • Begin at the top and move toward the bottom.
  • Repeat with the other eye, and then with both eyes together.
  • The smallest row of letters that you read accurately determines visual acuity in the uncovered eye.

How to interpret your results

The results of your chart reading will determine the quality of your eyesight. Your vision results will be expressed as a fraction. Fractions are shown to the left of each row and identify how well you can see. If you could read clearly to the fifth line, for example, your vision will be expressed as  20/40 vision. If you could read clearly to the seventh line, your vision will be expressed as 20/25. The numbers are given in feet, an American unit of measurement. One foot is about 30 cm.

20/20 vision: you see the same line of letters at 20 feet / 6.09 metres that people with normal vision see at 20 feet / 6.09 metres— this means your vision is perfect.

20/40 vision: you see the same line of letters at 20 feet / 6.09 metres that people with normal vision sees at 40 feet / 12.2 metres.

Monoyer Eye Chart


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  • Highwayman

    At the age of 30, I had a stroke which left me with a blind area on the right side and upper quadrant of both eyes. Five years later, I had my driving licence restored and have enjoyed 35 years of wonderful driving without so much as a parking ticket or speeding fine! Apart from someone smashing into the rear of my car when I was stationary at traffic lights, I have not been involved in any accidents or incidents. My eyesight has gradually improved and the blind area has receded, but when I tried to renew my driving licence at 70 years of age, the licence agency have decided this blind area does not meet the minimum standards! They will not renew my licence. I am absolutely gutted, devastated, and swamped by depression. This is totally . I wouldn't mind so much if they had some justification, but oh no. There is a line on a chart and 35 years of safe driving counts for nothing. Oh, without my specs, I can read line 7 on the Smollen chart, and with glasses, row 9! I can also identify all the numbers in the colour chart. When I sit in my car and look straight ahead, I can see the entire front windscreen and the door mirrors on both sides. I hope to win an appeal but I need the support of my doctor... but I haven't been treated for the stroke since 1993!

    • Gergana-Ekaterina


      Thank you for your comment and for sharing your story.
      We recommend following your doctor's recommendations and we wish you the best of luck with the appeal.

      Kind Regards.

  • Sue C.

    got to level 5 at 3 metres! yet my first visit to the optometrist says I needed glasses and was considered legally not able to drive!!! The specs he prescribed give me double vision and blurriness! I would NEVER consider driving in them! They also made me feel very dizzy when walking! I see perfectly well to drive and feel that he was just trying to make money!

    • Gergana-Ekaterina

      Hello Sue,

      Thank you for your comment.

      I am sorry to hear that you did not have a good experience with your

      We would suggest a consultation with another specialist, so you can be sure
      that a proper diagnosis is done.


    • Susan B.

      Hi Sue, you might be interested to know that on www.endmyopia.org they say yes, they ARE trying to make money and you can actually improve your eyesight instead of wearing glasses. It sounds as though the glasses were way too strong, not surprisingly if you can see without them! Anyway that's why I was here looking at the Snellen chart, because they suggest using it to track your improvements. There's a good interview here - https://www.youtube.com/watch?v=94D8Y6UmMtg.


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