Having trouble figuring out my astigmatism

So I have been trying to measure my astigmatism in the morning before I put on my glasses. Yesterday I realized I was probably measuring it all wrong. I was moving back until the second line made a complete double line. Oops.

Now yesterday and today I haven’t been able to see any difference in either eye as to one line sharper than the other. I think I see it, then I blink and both lines look the exact same. In both eyes. Before I was measuring 10 degrees in the right eyes and 170 degrees in the left. I don’t know if that is correct anymore.

I even went searching here and found the picture with just the spokes in the circle, black on white and white on black. I’ve tried both. I get a directional blur on both, but no one line actually clears up. On the bottom right I get a directional blur to the right and it continues. The blur is the the “up-side” of the line. On the left it is the exact opposite but still the “up-side”. I get closer to the top line and it just suddenly jumps from blurry on this side of the line to blurry around the line, then I’ve passed the 180/0 mark and it jumps to the other side. They are all blurry. I’m wondering if my high myopia is to blame.

It doesn’t help that I blink and they all change slightly. One line goes from having the all over blur to more directional. Another blink and it is back. It is like my eyes are going “nope, not going to let you know today”. I am just so beyond frustrated.

I have had no problem measuring my normal centimeters and they are pretty much holding steady at 19cm L 20cm R. Why is the astigmatism eluding me?

My glasses script is: R -9.25 Sph +1.75 CYL 110 Axis, L -9.50 Sph +1.75 CYL 083 Axis

Is there something I am doing wrong here?


Hi Zamirathe – are you having trouble measuring axis, or with the cm measurements to determine CYL?

Both I think. I am not even sure I am measuring the axis correctly. A little hard to measure the cm if I am not using the right axis.

Also with the measuring, I am not sure at one point I should be taking the second measurement.

Wow wait a minute - you can see 19cm and have -9.25 sph?!

I started at -5is, and that was 19cm…

So I see you have + astigmatism, not minus. I believe the tool is designed for - astigmatism.
I also found the directional blur change: I’d say that maybe, this means you don’t even really need that cyl… (Just a personal guess).

So if your cm measurements to blur are really 19cm (if I understand correctly ), I would go to an optometrist and see if he let me try on -5 glasses. Or just order some from Zenni?
Have a search here, there are some topics explaining more about those + cylinders - I didn’t bother to understand but it’s different from - cylinders! Maybe search online how to convert them, I think it’s not on the blog.

Good luck and keep us posted!

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I have done a bit of research and keep finding over and over that opthmaologists use plus numbers for astigmatism while optometrists use negative. A bit more research I found that it is because of how lenses used to be ground changed from on the outside (plus) side of the lens to the inside (minus) side of the lens. You can convert plus to minus and vice versa. Why ophthalmologists and optometrists don’t standardize it I don’t know.

So I converted my glasses prescription to negative astigmatism, contacts only use negative astigmatism numbers, and got my contact prescription back for spherical, cylinder, and axes. So I know that is right.

As for the tool I still haven’t been able to definitively tell any one axis, but I can see some vertical and horizontal shifting so I know I do indeed have astigmatism. I just can’t find the axis or cm with any accuracy I trust at this point.

Sadly I can’t afford a lens test kit that will work for higher myopia to test different things out on my own.

Yes Tii Chen, in the morning I come out to 19cm where my edge of blur sits. I am using a recipe I cut out of a cooking magazine as my text. However using a snellen chart at 3m in the same light I can just barely make out the 20/20 line with my glasses on. Everything smaller is just a blur. After a day of working on the computer, my eyes go down to like 12.5cm even using readers over my glasses. See my doc next week to hopefully get my first set of differentials. He has the machine to image the cornea so I’m curious what it shows.

This post has been edited to remove some incorrect info (multiply by two to get CYL)

@Zamirathe not sure if this will help, but here’s what I do.

First off, I don’t bother measuring axis. Opto axis measurements haven’t changed more than +/- 2-3 degrees for me over the past 20-years in either eye. I used the EM tool a few times to learn, and to confirm that the opto measurements were reasonable. They were.

As for measuring cm for SPH and CYL I am more comfortable using a different tool than the one on EM.

With astigmatism you are measuring cm for two sets of blur - an initial blur, and a secondary blur. The cm measurement to the first point of blur is essentially your CYL measurement, the second is your SPH. It helps me to think of the CYL correction as something that is layered over the top of the SPH correction.

I use something like the spoke diagram below and do the following:

  • Print the image on the right
  • Close your right eye and hold the image close enough to your left eye that all the lines are dark
  • Slowly move the image away from your eye until some of the lines begin to blur, like the image on the left
  • Measure and record the cm distance
  • Next, move the image further away to the point where the dark lines also start to blur
  • Measure and record the cm distance
  • Repeat for other eye

Now, the math.

  • Take the second cm measurement for your left eye and divide into 100. That’s your SPH.
  • Take the first cm measurement for your left eye and divide into 100. Subtract your SPH. That’s your CYL.
  • Repeat for other eye

Hope that helps.



Thank you! This has really helped a lot and I am more confident about measuring my centimeters now. I can actually see where the astigmatism changes the sight before the real blur starts. I have even been able to see that working on a computer all day actually changes my astigmatism reading more than my spherical reading and my left eye is significantly worse than my right eye.

Oh, and I was looking over my notes and went back to look at my old prescriptions. My original recorded axis is the exact same I recorded on the EM tool. Exactly 10 for the right and 170 for the left. Been seeing the same in the picture each morning too with the dark vs greyish lines. So just sticking with those numbers seems completely logical. Thank you for letting me know it doesn’t change much if at all over time.

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Glad it helped! Didn’t mean to imply axis won’t change. Seems to me one @jakey blog post mentioned someone getting three different axis readings in one day – all from optos. Since mine never changed much over the years, I just decided not to measure any more to reduce nuisance. Also, I’m planning to get rid of it anyway, so who cares? :wink:

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Thank you @Astigmatism_Assasin

Why do you multiply the CYL measurement by 2?

@itamar I looked for the source for this so you could read it yourself but can’t find it anywhere. Pretty sure I didn’t invent it. Believe the idea is that when you measure using this method you are measuring CYL in SPH equivalents, or maybe that’s what I convinced myself. I know you have a test lens kit, but have you tried measuring your CYL this way?


The way i understand it, the measurements of sph and cyl have the same units, thus, no need to multiply the resulting cyl cm by 2.

When converting cyl to sph in the prescription, you generally want to add x sph for any 2x of cyl you reduce, in order to stay close to the ‘circle of least confusion’ which should give you roughly the same amount of hyperopic and myopic blur on both the non astigmatic plane and the astigmatic focal plane

I find it hard to put this explanation into words, hope it makes sense…

Please measure your astigmatism using the methods described herein. I am curious to see how your results compare to your opto or test lens kit. Would you mind?

I would like to confirm my understanding, so this would be a big help. If you are correct, then I have been MASSIVELY over-prescribed for more than 20 years.

Thank you.

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@Zamirathe when you multiplied by two did your results approximate your opto prescription for CYL?

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Yes i am using similar technique to measure both sph and cyl cm

And i tested with the test lens kit and it is very close results.

For the left eye, dominant, the optometrist came up with a similar prescription, favoring 0.25D cyl difference
For right eye, optometrist difference from my xm measurements is about 1D cyl but about 0.5 less sph
So when taking spherical equivallence into account, the cm measurements are also very close to optometrist measurements, within 0.25D difference

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I have only done 3 measurements but so far it varies. First one was within .25 dioters of my prescription. Each day it is only going lower. The third one today surprised me, both eyes dropped a full diopter from 2 days ago.

Not sure if it is accurate though. I woke up dizzy today and had trouble just walking and standing, so my MS is acting up again. Always happens when there is sudden heat/cold changes. :frowning: So I can’t be sure if this is also a result of the MS or just my eyes really liking the fact that I wore +1.5 reading glasses while at work all day yesterday. (Today I had to drop down/up to +1.25 glasses.)

@itamar thank you for catching this error.

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So today I found out that the ruler I printed from the site is so far off in measurements compared to my centimeter flexible tape. The 2cm is 3cm on the printed diopter meter, so all of my measurements from the past 2 weeks is probably all wrong.:frowning:

So I think I am going to have to invest in a lens kit eventually. Strangely enough, I think my astigmatism is decreasing. I noticed a difference in the halos around lights and the blurry images when not wearing my full script.

So for the astigmatism, do I still multiply by 2 or no?

No multiplication necessary. I re-read the measurement section and that was incorrect. Sorry about that.


I don’t get it, I did the calculation and the results don’t mean anything to me, can you give an example please?

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Have you been able to find the first and second point of blur in each eye?