Question About Astigmatism Reductions

Last year, in July, I got my very first pair of differentials that were reduced 1.50 diopters and my very first pair of normalized glasses that were reduced .50 diopters. I know I am super late, but I recently went to the optometrist to do my second reduction in my differentials.

My cylinder prescription in my PREVIOUS differentials were -1.00 in my right eye and -1.50 in my left eye. The astigmatism prescriptions for my NEW lenses are now -1.00 in my right eye and -1.75 in my left eye. (NOTE: My eyes did not get worse. My true astigmatism prescription is -1.00 and -1.75, however my optometrist decided that the change was too small to put in my previous differentials.)

I never talked to my optometrist about under correcting my astigmatism, so my cylinder prescription is my true astigmatism prescription in my differentials, which is -1.00 in my right eye and -1.75 in my left eye.

I know that using my new lenses would be beneficial because my spherical is reduced .25 diopters, but I was wondering if using my new differentials would cause my astigmatism in my left eye to get worse, since my cylinder prescription was previously -1.50 and now it’s -1.75.

What are your 20/20 sphere and cyilnder numbers?

For finding out the right cylinder correction, if you want to improve astigmatism or just correct it, there is no better way than try out cylinder test lenses, because of your individual distance.

Of course using higher diopters is not good, if the previous diopters were ok for you. It will probably make astigmatism worse. If you have improved to -1.5 in your left eye, then -1.75 would be worse. But if your left eye is at -1.75, then you won’t make anything worse.

I know that there is an online end myopia tool to see what spherical prescription you have, but do you know if there is a tool I can use to see what astigmatism prescription I have?

On my last eye checkup, which was a few weeks ago, all my optometrist said was that I was seeing better out of my lenses, but my true prescription has not changed.

you could only find out the degree with an “astigmatism 360 degree line test picture”, but finding out the cylinder diopters is even with a test lens kit not easy, espacially if you are not sure about the degree. And in the beginning it is even more confusing.

I have bought EyeQue VisionCheck and it gave me the correct cylinder values,
I have confirmed them with test lens kit.
Without that device, I would really need to go to an eye doctor or lens shop,
because I think it is really not easy, almost impossible for beginners.

when it is about astigmatism correction, nothing is better than a test lens kit and some values (especially correct degree), which you can test out.


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image
Can you walk me through on how I could find out the degree with this image?

Just move from very blur distance slowly closer to the picture without any glasses and see which lines are getting clear first. I have made a detailed degree pic I will upload later.

The other way can work even better. Move from clear and close distance to blur and far distance and see which lines are the last which remain clear.

Test lenses are extremely helpful for astigmatism. I had -0.75 CYL of astigmatism in my left eye according to an optometrist, but I found I could see perfectly clearly with just -0.25 CYL, and now I don’t need it at all. You might find that you either don’t need astigmatism correction at all (most people who wear contact lenses don’t get the kind that offers any cylinder), or you might find that you can see perfectly with much less CYL than you were initially prescribed.


It is anyway impossible with this test to find out the correct degree.

For me the easiest is to start with the 4 circles with the parallel lines from the above post.
image

The more detailed, the more precise the astigmatism fans / circles are, the easier it is to get lost with them, i.e. be unsure about which line has the most blur.

With the 4 circles I go as close as needed to get the lines black and equally sharp on all 4 directions. Then I start increasing the distance and notice which one goes grey or blurry first.
Because cyl can be different per eye, I’d recommend measuring it per eye.
This basic test will give you an idea if you really have an astigmatism (transient or permanent) issue at the moment. But note that astigmatism can change in power and in axis quite quickly especially if you are not wearing corrections for the cyl. I could get 5 different measurement from 5 different optos within 5 days. Different in axis and different in strength…

I most typically have cyl prescribed by optos around 90 degrees (anything from 86 to 104 degrees, and 0 to -0.75D in strength), and not surprisingly the first circle that blurs is the one with the vertical lines. Because I’m just checking the presence of astigmatism but I do not add to corrections, it is enough for me to know it is around 90 degrees and if it is significant or not on the given day.
But I could then go on looking at the more detailed drawings, do the same process to figure out if it is 85, 90 , 95, 100 or 105. Then I could go further with test lens kit or other tools to guess what in between the 5 degrees exactly.
20 years ago, most optos corrected to rounded 5 or 10 degrees, nowadays we can measure so well that optos prescribe cyl by 1 degree. But all optos I talk to admit that the error is minimum +/- 5 degrees, but sometimes it is +/- 15 degrees, because the “which is better this or this?” question is very subjective.
20 years ago most optos - at least the ones I met - started to convert cyl to sph automatically if cyl was measured above -0.5D to keep the prescriptions with low complexity and to allow for contact lenses without cyl correction (because the ones with cyl added rotate constantly on the eye making them super uncomfortable)

Whichever is the direction of lines that blurs first, that will be the axis corrected with cyl if you let the opto do that.

This picture shows what you should see before you start increasing the distance (right side) and how the blur appears first (left side). So in the example the blur appears around 10-11 or 4-5


Source post

Looking at a test lens frame that 10-11 / 4-5 will translate to a cyl correction at about 120 to 150 degrees.
image

Note: The cyl correction in the glasses is stronger diopter added on one line like this (obviously then worked together with the main diopter so the edges are not as sharp as on this pic but gradually changes from the cyl extra to the main)

image

So the cyl is one line but your eyes can have uneven surface and have a main angle and a secondary angle. That’s why in my opinion 90% of cyl corrections is almost pseudo scientific… All depends on how you are that day and you might unconsciously tweak the result by turning your head or eyes left and right or up and down by just a few mms…

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I dont believe in quickly changes of the astigmatism. I think the used devices have different calibration.
Im happy that I have Eyeque’s Visioncheck, so I will trust only its results.
But I just started with measuring astigmatism. I will track how fast it changes.

There’s a big mental component to astigmatism and there’s also some evidence that it’s something you can get under conscious control (just like you can cross your eyes or wiggle your nose or ears…) Lasik surgeons have noticed that posture changes astigmatism (people get a very accurate reading in the office while sitting down in front of the machine, and then have different values when they get another very accurate measurement while lying down on the operating table.) Even sitting quietly and relaxing for a 20 minutes can change astigmatism values significantly.

It’s like blood pressure. If you start thinking about something that makes you nervous it can go up. If you relax it goes down. It changes all the time based on what you’re doing and what you’re thinking.

You might experiment some with your device and find that you can get different (accurate) astigmatism readings with the same equipment without calibration issues.

https://eyewiki.aao.org/Physiology_of_Astigmatism

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What I was talking about is my experience with different optos measuring my eyes on different days in a row. The measured axis and the measured strength changed from opto to opto which proves that there is a big element of guesswork on astigmatism measurement even in the “big official opto world”.

Many people don’t believe that most people could get different astigmatism prescription from different optos within the same day - at least they don’t believe it until they try it on themselves.
And if you only get one measurement and that happens to go bad and measure a silly axis with too much cyl then without EM you’ll take those glasses and get your eyes and brain used to them. :confounded:

So I wasn’t talking about tools like Eyeque’s VC measuring completely different axis and strength (I don’t know if that would change and how much - but I’m quite confident I could influence EVC’s result, too, though most probably to a lesser degree). I was talking about optos doing a measurement with autorefractor and then turning it into a prescription after trying test lenses on you. The latter can give totally different results - depending on the opto’s preference and bias and belief, on the lights and quality of the signs to read as well as your tiredness or anxiety or posture.
I tested multiple optos with getting my eyes measured several times just within a short time and ended up with the mentioned 20 degrees and 0.75D differences in the opto measurements.

In my view the reality with 99% of people is that they go and get their eyesight checked by optos working with an autorefractor and test lenses. And they only visit one opto. And that is the measurement they accept.

So I’m just raising awareness of optos not holding the truth about the cyl measurement and corrections.

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Yes, that’s why I would not trust anyone’s measurements any more. Especially the cylinder correction has a high risk, that it is not accurate. I think also most people just accept the one measurement and this causes probably more lens-induced astigmatism. Mainstream is so screwed.

But still before using EVC, I thought I could never find out the right cylinder values just with the test lens kit. I needed some values, which I can confirm or test with.
So I would advice use EVC or get 3 measurements and confirm the right cylinder correction with test lens kit and snellen at 6 meters with the big E letter.

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