The Centimeter Measurement

You already learned how to do this from my e-mail.

The e-mail was a bit of a teaser but hopefully you took a moment to measure your centimeter there.  If so, well done, you’re well ahead of the curve already.

If you haven’t, let’s revisit that e-mail, and this time you’ll really want to do the measurements.


This is a foundational principle.

The measurement tells us what your prescription should be, it also tells us a lot about eye strain.  And perhaps what matters most is that you’ll be able to log your progress quite efficiently with the centimeter measurement.

Like building blocks, these sessions often build one upon another.  We’ve got the egg timer to make sure you get enough time to do each.

Right?  Right!

Let’s recap the way to measure your eyes.

A flexible measuring tape is best.  Preferably a small, roll-up one. They are usually sold at fabric stores or for a few cents on Amazon – this one, for example.  If you don’t have a measuring tape but do have a printer, you can print my diopter measuring tape (an invention of my own – very, very handy – link below).

You need the ruler to be able to measure the distance of your eye to a page or screen.

Here’s how you measure:

1.  Take off your glasses.

2.  Look at your screen (or a book, printed pages are best).

3.  Start close enough that the text is perfectly clear and slowly move back until there is the tiniest bit of blur. You want to stop just where the text stops being totally sharp.  Any change in sharpness, that’s your distance.

4.  This distance is however many centimeters from your eyes to the page or screen.  Now get ready for the thing that blew my mind when I first learned it:

Diopters (the number that defines the strength of your glasses) are just inverse meters.

Get it?  Diopter converts directly to a distance number (as in the centimeters you recorded in your distance to blur).  It really is shockingly simple, like a lot of things you’ll learn from me.  However far you can see before blur, that distance directly converts to how many diopters you need for “perfect” distance vision.

Not clear yet?  Let’s use an example:

Let’s say your prescription is -4.50.  It was derived at the optometrist, with the chair and the dimmed lights and the lab coat and all the fancy gear and smoke and mirrors.  It seems as though it’d be impossible for you to figure out this number on your own.  But now you realize:

That -4.50 diopters is just another way of saying, “22 centimeters till blur”.  

If you start to see the tiniest bit of blur on the page at 22 centimters then you need exactly a -4.50 diopter prescription to see an eye chart clearly, past the 20/20 line.

That’s it, nothing more complicated.

Take that in for a moment.

I actually created a calculator that translates centimeters to diopters for you.  Just plug in your distance to blur, and it’ll tell you how many diopters the distance equals (link below).

Realize now why I call the optometrist office a magician’s stage?  Why it’s a charade? You probably still can’t quite believe that this is true, that you can use a ten cent ruler to figure out your prescription.  But look it up, diopters are just inverse meters, nothing more.  And the only measurement to determine inverse meters (to blur), is the measuring tape.

Now the opometrist comes to the same result a different route.  It’s not better, it’s just more fancy.  And yes, there are other things we could talk about here: accommodation range, lighting, astigmatism and so on.

But I want you to free your eyes.  I want you to stop having to depend on prescriptions.

And the way we do that is by learning the simplest things; the way out of the maze.  We’ll get to other things, like astigmatism, a bit further on.  That’s quite simple too, not to worry.

Let me give you some tools so you can start to try this yourself:

Here is how you convert your centimeter result to diopters using my calculator.

** NOTE:  Very Important – Your Results Will Possibly Be Surprising. **

I tell you that you can replicate the equipment at the optometrist with a ten cent ruler.  And yet your results might give you a different prescription.

I’m going to explain in detail what is going on with that, how the ruler does the same as the optometrist, and why your prescription numbers will possibly vary from your centimeter results.  Some of it will depend on how long ago you got your prescriptions, how your eyes have changed, whether you were overprescribed, and most importantly, how your eyesight varies throughout the day.

This will all make sense once you try it and go through the next e-mails.

For a picture of how the measuring tape is used, go here.

It’s really simple once you get the hang of it!

These are the first steps.  Take them and you’ll feel compelled to go on and get your eyes back.  Take this little bit of action to come up with a measurement result and you’ll no longer be a passive victim of myopia.


Record the results for your left eye and right eye.  Do it in the morning before you start work in front of the screen, do one at mid day, and another in the evening.

Write down the results.  You’ll need them for the next part tomorrow (where I’ll show you how those numbers tell the future of your eyesight).

Here’s what that will look like:


Left: 22cm  Right: 26cm

Mid Day

Left: 21cm  Right: 25cm


Left: 19cm  Right:  22cm

These numbers are an example obviously, but how they change says a lot about where the problems are with your eyes, and how you are using them.

Action Item

If you already have the numbers, find that piece of paper (or Google doc sheet) for tomorrow.

If you don’t, get to measuring!  😉

We’ll start building from there and then add the eye chart (Snellen) to give you two different perspectives on your eyesight.

See you tomorrow!


– Jake

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