Snellen Chart

Obtain a Snellen chart by clicking on this text

Once you have a Snellen chart, use this article to learn the following:

I.  What is a Snellen chart

II.  How can the Snellen chart be used to improve eyesight

III.  How can I convert a Snellen chart reading to a fraction of 20/??

IV.  How does the visual accuity on the Snellen chart relate to diopters?

I.  What is a Snellen chart

A Snellen Chart is an objective way of measuring visual accuity.  Basically, 20/20 means this person sees from 20 feet what a ‘normal’ person sees at 20 feet (so this is normally known as perfect eyesight).  I have 10/40 eyesight at the time of writing this page, which means at 10 feet I see what a person with ‘normal’ eyesight would see from 40 feet.  These fractions can also be in meters (6/6 is the metric equivalent to 20/20).  Better than normal eyesight is also possible.  A person with 20/10 eyesight sees at 20 feet what a person with ‘normal’ eyesight would see from 10 feet.

With the chart these fractions are made in the following way.  The distance from the chart is the first number.  The number written on the chart for each line is the second number.  For example, if you stand from 10 feet, and you can read the big E correctly on the chart from the link marked 200 feet, then you have read 10/200.  In meters, this is 3/60 because you are 3 meters from the chart and reading the line marked 60 meters.  Read each line of letters.   The lowest line that you can correctly read at least half of the letters on that line correctly is your visual accuity.  For example, say you stand from 15 feet, and you read (on the chart provided above) the following:  On the 200 line the big E correctly.  On the 100 line the F might look like a P and you also see the P as a P.  On the 70 line  you see some straight lines where the T is, you see the O, and you see a smudge where the Z is.  Then your visual accuity is 15/100 because you read half of the 100 line correctly, and less than half of the 70 line correctly.  An optometrist would write 15/100 (-1) to show that one letter was missed.

Please note!  Visual accuity will vary with different lighting conditions and will often depend on your mood and other factors such as the contrast, letters, and typeface of the chart.

II.  How can the Snellen chart be used to improve eyesight

Here is a brief summary of this topic and at the end I reference some of my blog posts which go into more detail on this.

I think the Snellen chart is an excellent learning tool for learning to see clearly without glasses. If you don’t like the Snellen chart, a calendar with different sized numbers can be used. The main thing is to have something on the wall that you have memorized the numbers/letters of. Reading the Snellen chart or reading the numbers from a calendar isn’t a test, it’s a way that you can best experience improving or worsening of vision. For example, if I stand in front of the Snellen chart and think I see a letter, and then suddenly I can’t, then I immediately know that I was staring or doing something else wrong. If I breathe naturally and blink, ever so slightly swaying, I immediately notice that I can read more letters and I know that what I just did was correct and I should do it more often! In this way, I’m essentially training my whole body on a conscious and subconscious level to recognize what movements produce good vision and what movements produce poor vision. When I’m at work talking to someone or writing on my computer without glasses (like right now), I can remind myself to do the ‘good’ motions and, tada, I can see better. That’s how it works, a very gradual learning process, and that’s this practice should be done every day as Bates instructed.

I definitely find that when I read the chart with one eye, then the other, and then both together, that my vision clears much faster. I don’t know why this is! However, this is the method that Bates recommended for reading the chart.

There are many other activities one can do in front of the chart such as looking at smaller letters (smaller copy of Snellen chart) close up and then at the same letters on the chart further away. Dr. Bates wrote about many different methods in his magazines and book.  However, I think just by being creative and trying different things like different distances and swaying one can learn a lot. Keep it fun! If you are bored then make a game out of it somehow like looking for all of the letters with corners and then looking for all of the letters with round edges!

Practice from different distances, different sizes of letters.  Each day improve the darkness or clarity of a letter, and don’t worry about whether that is the best or worst that you’ve ever seen.  The vision fluctuates, and  through the temporary improvement that you learn on the chart, permanent improvement will follow.

Therefore, the most important thing is to learn something each time about what makes your vision better or worse.  If everything looks blurry and you are getting frustrated and straining to see the next lower line, that is a sign to move closer and practice something fun with a larger letter, or to stop the practice for that day.

Creativity is key, the basic requirement is just to do for a few minutes daily up to however much time you can still have fun with it.  For more information, refer to these posts:

Snellen Chart Practice – Part I
Snellen Chart Practice – Part II (coming soon)
Snellen Chart Practice – Part III (coming soon)

III.  How can I convert a Snellen chart reading to a fraction of 20/??

First keep in mind that converting these fractions is only done so that readings from different distances can be compared.  The conversion is only approximate.

The main principle is that the Snellen chart fractions can be reported in multiples, and it still has the same meaning.  For example, if you can read the 10 foot line of the Snellen chart from 5 feet, that is 5/10 eyesight, or approximately the same as 10/20 eyesight, or 20/40 eyesight as it is most commonly referred to.

Here’s a more complicated example.  Let’s take one of  my first readings where I read the 200 foot Snellen chart line from a distance of 193 cm.  First of all, the units aren’t the same, I need to change 193 cm into feet.  193 cm = 6.33 feet.  That means I had 6.33/200 eyesight.  It’s important that both numbers in the fraction are in the same units (both in feet, or both in meters).  Now to convert this Snellen reading of 6.33/200 to a fraction of 20/???, do the following:

STEP ONE.  divide both numbers by the first number.  6.33/6.33 = 1.  200/6.33 = 31.6.  Now our fraction is 1/31.6.

STEPH TWO. multiply both numbers by 20.  1*20 = 20.  31.6*20 = 632.  Now the fraction is 20/632 eyesight.  I usually round to the nearest 10 so I would report this as 20/630 eyesight.

IV.  How does the visual accuity on the Snellen chart relate to diopters?

There is very little correlation from the Snellen chart accuity to the refractive error in diopters that an optometrist would give you. Five people with a prescription of -3 diopters might all have different visual accuities without glasses ranging from 5/100 to 5/10!

Why is this?  As you will learn from the pages on the rest of this blog, the use of the eyes with glasses is fundamentally different than vision without glasses.  Different people will srain in various ways to see through their glasses.  This strain may be mental and/or physical, and these differences will affect the visual accuity without glasses.

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24 thoughts on “Snellen Chart

  1. Howdy,

    I love your postings, its just so great the way your vision improved in such a short time!
    One of my slower students now reads your blog and has started practicing more with some improvment.

    Trying to put new thumbnails of BEM for you on cleareyesight.info.
    See page 32 and 33.
    Also got new saccadic sunning pic/chapter.
    More on the way.
    Im going with Greg Marsh.
    Teaches lots of new methods.
    Thanks for recommending him!!

  2. Pingback: Book Club: Snellen chart « Seeing Beauty

    • ok, I turned off the nesting comments feature since it seems to be really annoying! This is a semi test… but I guess we’ll figure it out the next time there’s something interesting that gets lots of comments.

  3. dear sir ,

    i have a question ?
    please give me an answer
    how much angle will subtende by the largest letter of snellens chart at the nodal point of an emmetropic eye at a distance of 6m

    • Hi Sarath, it is quite easy to calculate the angle that the eye must move to look from the top to the bottom of the letter. the height of the top letter of Dr. Bates’s eye chart was 3.5 inches, which is .0889 meter. Taking the inverse sine of .0889/6 gives an angle of 0.85 degrees. So if the eye looked at the top of the letter, and then the bottom, it would have turned just under 1 degree.

      If, on the other hand, you are interested in the angle of the rays coming from the top and bottom of the letter through the lens, cornea, etc of the eye and their relative angle at the center, as I think you are, then the answer is more complicated and I’m not sure. I’m guessing you are curious because you would like to know the extent on the fovea which the image projects?

  4. Hi sorrisi

    recently i have attended an exam actually this Q is from that exam in its answer key i found it is
    5 minites

    but i strongly feal that this answer is wrong

    rigt answer will be 50 minits

    • hhmm, yes, I agree, at least from my calculation 0.85 degrees is about 50 minutes. what I don’t know is if the effect of the lens! interesting problem.

      sorrisi

  5. Hi I have myopia of 800 degrees. Will this method still work for me? And can I still wear my glasses during the day? Cause I really can’t see anything without them. Thanks !

    • Hi Ribbon, I don’t know what 800 degrees of myopia means. Is that 8 diopters? If so I started with -8 glasses and this method is working great for me.

      The best way to find out if it will work is to try it. Have you read Dr. Bates’s book and his magazines? It takes some amount of study to teach yourself, or you can hire a teacher.

      There are some quick things you can learn like palming, swinging, and central fixation. In addition, learn how to recognize if you are relaxed or under a lot of strain (and then how to release the strain). Learn those things one at a time, and you will discover which ones improve your vision. The improvement is temporary, but if you continue to practice until it becomes a habit then the improvement becomes permanent.

      I have noticed that improvement is faster without glasses, but I did and still do wear weaker glasses to do my work. Gradually I got weaker and weaker glasses. I always practiced the Bates method without glasses though and also increased the number of activities I can do without glasses.

      Cheers,
      Sorrisi

  6. Pingback: Snellen Chart « Seeing Beauty

  7. Hi S,

    The snellen chart practise doesn’t help me. I tend to strain when looking at the writing. I still haven’t quite figured out how to view letters without strain. I get clear flashes when I’m outside walking etc. not paying attention to my sight however the Snellen chart is different.

    Can you suggest somethings on how to look at letters without strain?

    • Hi visitor,

      I will be writing a post soon about this, it’s a more challenging one to write than other topics because there are so many ways to do it and everyone has a different experience!

      The problem is that you are thinking about your eyes and trying to see while looking at the snellen chart. Imagine the white around the letters to be whiter than you see it. In fact, don’t even try to see the letter, just look at the white around it. If a letter pops out at you, then dodge it and look at the white space around the next letter.

      Another suggestion would be to choose a more suitable distance: look at the card from where you can read about half of it easily. Alternate looking at the letters you can easily see and the smaller ones.

      Here’s a third suggestion – think of a word that begins with that letter. Can you think of a positive word? Once you do, associate that letter with that positive word when you look at it. And remember, you never look at a whole letter, just small parts of it at a time!

      Sorrisi

  8. Hi S,

    Thanks. That’s some really good tips. I tried it successfully – I notice there’s clarity but there’s a lot of smear too. Double vision etc. I know you mentioned this clears up in the long run in your other posts.

    I have another question though…have you perfected the universal swing? I look at the snellen chart and it is not swinging. When I put effort into making it swing every blurs.

    • Hi visitor, I’m glad that those suggestions helped.

      Well, I wouldn’t say I have perfected the universal swing since my vision is not yet perfect. But when I practice it, my vision always improves. What you wrote: “I look at the snellen chart and it is not swinging. When I put effort into making it swing every blurs.” provides a very big clue to what you are doing wrong. The vision will not improve by putting effort into it. Think back to some of the things you have told me that helped you. In general, it is things where you aren’t really trying to do something, it is rather becoming aware of something. It’s important to approach the Bates method with a bit of fun, it keeps the background thought of ‘trying’ away.

      So, instead of putting in effort to make the card swing, just let it swing when you move. One easy way to notice this is to stand in front of the chart and hold one finger infront of you. sway your body and your hand together, while watching the finger. You can look at different parts of your finger tip. As your body is swaying side to side and you watch your finger, you will see the chart moving in the background in your peripheral vision. In fact, the entire room will be swinging in the background. All the while, you are seeing your finger best. This is the easiest swing to accomplish. Now, to get the universal swing, it’s easier to be looking out a window. Look at something far in the distance, the house across the street or a tree in the distance. Now sway side to side, but this time look into the distance. What you might notice now is that objects close to you such as the window frame and curtains, are moving in the opposite direction as you are. In the distance, the objects like the house or tree appear to move with you. When you walk around outside, you may notice something similar, but perhaps more subtle. The universal swing is all about noticing how objects at different distances move in your peripheral vision relative to what you’re looking at.

      happy new year!
      sorrisi

  9. Hi Sorrisi!
    I’m new on the Bates Method and I need your help 🙂

    When I shift from one letter to the another by using the eyechart, will I have to see the letters best(with most clear) or just can see them(with most blur)?
    And on which line of the chart I should use for the practice?

    And when I palm, should I remember black or just don’t think of anything except for being with breath?

    Thanks for your reply,
    Alex

    • Hi Alex, if you could let me know how you learned the Bates method so far that would help. also if you’re nearsighted/farsighted or have other problems.

      I don’t understand what you mean in the question about shifting, I’ll get to that below. First of all, stand from a distance where you can read half of the chart (it may be quite close!)

      Remember, the point is to just observe what you do (or don’t do) and how that affects your vision. So use what you learn from looking at the chart throughout the day.

      When practicing shifting, look at a letter you can read easily. You should observe that you can see that letter best. You should also observe that although you are looking at one letter, you can still see the other letters. But the letters you are not looking at are blurrier. It’s not that they are blurry or clear, it depends how far away something is from what you are looking at. What you are looking at is clearest. The periphery gets blurrier the further away it is from the center. Does that make sense? Now look away to a smaller letter that is not seen so easily. Can you observe that (although it might not be clear) it is now clearer than when you were looking at the larger letter? Can you observe that when you look at the smaller letter the larger letter is now seen worse than before? If all of that doesn’t make sense, let me know! It’s not as complicated as it sounds in writing.

      see my last two posts on palming. Basically, experiment, and do what is most relaxing for you.

      cheers,
      Sorrisi

      • Hi Sorrisi, In fact I found the Bates method about a year ago on the internet and at the first time I was amazing if this method is possible for me to throw away my glasses, but it’s quite not easy to get rid of the poor eyesight as I thought, so I am about to ignore them. Now my eyesight is about -4.00D. and I’m going to try for the method again if I have enough time for the practice because I rarely find out much time for the practice which I think it’s impossible for one student who has to study hard throughout the day to improve his vision.

        I quite understand what you have written, but there are some points that I would like to ask you more: when I first look at the letter that I can see best, do you mean that this letter is to be clear as when I was wearing the glasses? and I don’t understand ,after we look at the smaller letter, how is it clearer than when I was looking at the larger letter? and then with this practice, how can I improve my vision?

        Can you tell me how was your vision before you found out this Bates method and how is your vision right now?

        Thank you for your help, Sorrisi.
        Wish you success on your way!!

        Best wish,
        Alex

      • Hi Alex, from your first paragraph, I think it is essential that you get a lesson with a Bates teacher. It will be money well invested and otherwise it is likely that the time you spend now will be wasted (because you’ll quit the next time you get busy). A good teacher should be able to show you within 1 hour some things that will work to help your sight. Of course, you won’t come away with perfect sight, but you will at least know some things you can do in the limited time you have. In fact, Dr. Bates often made the point that every moment the eyes are open is an opportunity to improve them. It’s not about exercizes, but learning to use your eyes properly. A teacher will help you achieve this faster than learning on your own. If you aren’t willing to pay a teacher, then the price you have to pay is with your own time teaching it to yourself – this may be something you don’t have time for. But once you understand the method – everyone has time for it no matter how busy they are.

        Now, in your second paragraph, seeing without glasses is different than with glasses. You see one point best, whereas most people with glasses think they see everything best all at once. This is what the shifting is supposed to teach you. Here is a more simple exercize. Hold up both pointer fingers in front of your face about 6 inches apart. Now look at the left one. Can you see your fingerprint? Bring it closer until you do. Now as you are looking at the left finger, wiggle your right finger. You can see it right? But it is less clear! Now, look at your right finger. Can you see the fingerprint? Can you see that the left finger is now blurrier? This is a simple demonstration of central fixation. It may seem far to simple to improve your eyesight. But what you do is gradually become able to distinguish between finer details, at greater distances. How? In the example I gave you, by moving your fingers closer together and demonstrating the same thing, and then movng them further away.

        Does that make the practice on the chart make more sense? If not, try reading the chapters Dr. Bates wrote on central fixation and shifting. Do you have his book?

        Here is a summary of my progress so far: https://sorrisi.wordpress.com/vision/. I’m writing my phd thesis right now, so I’m not putting as much time into my blog or teaching until I’m done. But keep me posted as you try things out and I’ll help as much as I can,
        Sorrisi

  10. Hi Sorrisi, you are right that I should find some teachers to help me, but the problem is that in my area, there are not any Bates’ teachers, so the only way to deal with this problem is to learn it by myself with the Bates’ book that I downloaded it from the internet and another Relearning to see : Improve your eyesight naturally.

    While I practicing central fixation with the Snellen chart, will I have to see the letter clearest(not blur anymore)? Because it’s somewhat I can’t find in the Bates’ book.

    Wow! you are studying PhD.? That’s so cool!
    I wish you have finished your thesis soon, and I would like to thank for your help, maybe I would like to ask for being my consultant.
    Thank you again 🙂

    Best wishes,
    Alex

    • Hi Alex, great – well, if you’re teaching yourself, I hope you can manage to stick with it, it really is worth it!

      There are some teachers that do distance lessons. I haven’t tried any myself, and it is rather expensive, but it is an option.

      When practicing central fixation, think of this – you want to see best where you are looking. Gradually with practice that will get clearer. The most important part is to continuously demonstrate that the clearest part of vision is in the center, and everything else is less clear.

      If you see everything with the same clarity, then it will all be the same blurry. If you only see what you are looking at, then you are staring and the vision will blur.

      So to do it correct, see best where you are looking, and worst everywhere else. And then shift your gaze to look at something else at every moment! Does that make sense? Search my blog for “central fixation”, I’ve written some posts that might help you.

      Hopefully that helps!
      Sorrisi

  11. Pingback: Snellen Chart Practice, part 1 « Seeing Beauty

  12. Hi sorrisi.can you tell me in easy language that what is central fixation.and I am doing sunning,palming and reading snellen charts but I want to know that how I can relax my eyes in these exercises or I can say that how I check that my eyes are relaxing

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