Astigmatism Doubts

Hello
I know there has been a lot of astigmatism post lately in the forum and here is another one. This might be a silly question. I always see in several post. Where Jake mentions if you have more than -1 D of astigmatism than you can gradually reduce the correction down the road. If you have less than -1 D of astigmatism you can drop it and replace it for spherical. What if I have exactly -1 D of astigmatism in one eye? What approach is suggested or usually taken?

On a Side note this is not a diopter specific question but I notice that when I look at the eye chart from afar I really cant tell if I have astigmatism blur. I can’t notice it however when I do the line tests I can see some lines bolder than others. I’m not sure if dropping astigmatism will be the best option or just leaving it on. I have tried on a test lens kit and don’t notice much difference when looking at the snellen chart.

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I believe astigmatism is more tricky to reverse because it’s a cornea’s aberration and AF will not change the shape of your cornea.

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It could be a cornea aberration. Usually it’s just that the eyeball didn’t elongate in a straight line but under an axis, You can solve it with AF and replacing some astigmatism with a little extra spherical added (in most cases). You’d wanna eliminate the axis from the total equation. This will make future reductions much easier.

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i made my first reduction four months ago in this way:
Original Prescription -4L -3,75R and CYL +0,75 both eyes
Normalized: -3,75L, -3,5R, +0,50 CYL

Now i’m using a-3,25 both eyes without CYL correction to look the PC screen at the TV in my living room (about 3 meters), and can see most small letters with no much effort, but constantly blinking to produce more clarity.
Sometimes i check my more myopic eye status and seems to get better.
I’m a afraid i’m doing some thing wrong, because i’m also learning english and must missundertood some things.
I’m glad to talk with more advanced students.

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i have founded this gem
i took a time to watch because is 1 entire hour last long!
hope help you guys

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This was helpful. Thanks for the post. I do notice that when I don’t ‘try’ so hard and just relax, I improve faster.

glad i helped. good look at your vision improvement

Since the two different notations of cylinder had me confused before (as if astigmatism as such wasn’t confusing enough already), it might be worth noting that your astigmatism cylinder can be indicated as either a positive or a negative cylinder value on your prescription (it seems to be a random choice by country, profession, personal preference or maybe the weather).
One notation can be converted into the other one. The conversion affects both the sphere and the axis (90 degree change). Basically -2.00 SPH +0.50 CYL 10 Ax is just a different notation for -1.50 SPH -0.50 CYL 100 Ax.
Thus dropping a plus cylinder should have a different effect on your choice of sphere than dropping a minus cylinder. If you just adapted sphere like ‘add 0.25 for every 0.5 cylinder’ no matter the notation, you would otherwise end up with two very different results for basically the same original prescription, in the case of the above example:
-2.25 SPH for the ‘plus’ notation vs. -1.75 SPH for the ‘minus’ notation. My guess is that the negative cylinder is the more common one in EM and that the suggestions in general refer to negative cylinder values (so the -2.25 would probably leave you somewhat ‘overcorrected’ in an attempt to reduce cylinder complexity).
It would be great if someone with more knowledge about the matter could confirm whether the general advice as to handling the reduction of cylinder complexity does indeed refer to the ‘minus’ notation.

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the astigmatism notation must be interpreted by the optometrist.
If you are nearsighted (minus prescription) you probaly will start to notice astigmatism blur before myopia’s blur when you’re puting away an object far from your eyes.

try this:
astigmatismtest
26cm

This means if you your axis is 180º, the blur will appear in horizontal way, with sharpness in the vertical way. So, if you see perfectly sharp at 25cm, and at 30 cm you notice a horizontal blur, this means you’re more myopic in the horizontal way. In order to correct this aberration, you need to consider the minus from the myopia combined with the minus from astigmatism.

A plus astigmatism prescription would weaken the minus prescription, but only at the perpendicular edges of the cylinder axis. So you need to put a stronger prescription only at the left and right edges of your sight.
:
For example (the amount of diopters are slightly random):

  • image starts to blur at 30cm = -3,00 Spherical

  • 180º sharper line noticed at 25cm (blur kept at left and right edges) = - 0,50 90º . This will need a cylindrical correction, which is -3,50 myopic only at the left and right edges, and still -3,00 vertically.

Most optometrist uses the plus convention for astigmatism, so the CYL would be +0,5 180º, which means the vertical axis will be weaken by the CYL correction, keep the vertical axis proportionally less myopic than the horizontal one.

So if you see -3,0SPH and 180º +0,50CYL at the prescription , the glasses manufacturer understand this as a sharpness on the vertical way and the need of more prescription at the horizontal way, (because the spherical prescription is the stronger one) and actually will manufacturate a -3,50SPH 90º +0,50CYL, keeping the horizontal axis at -3,50 and backing the vertical to -3. It’s the same thing, doesn’t matter.

I’m actually, had this doubt at the zenni optical website, and just ignore my CYL and order an only SPH glasses.

Result: after three weeks, my astigmatism seems to be weaker than before

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Wow thank you. Now I know what cause my astigmatismI I will post an update in a month

I have not watched the video yet and don’t consider myself having more knowledge.
But I can confirm that reading the EM blog, I also understood that reducing prescription complexity refers to - cyl.

I think @FMR has been reading on this, if I remember correctly?

Yes and no. Technically, notation makes no difference if you understand what you’re doing. But in practice, it’s easier (at least for me) to think in terms of certain notations in different situations.

Let me take a look.

@Bridge, I read your post, and I agree with everything (without having read any other posts in the thread yet, though). You have it down perfectly.

So, I think what you’re trying to clarify, is whether or not minus cyl notation is the one in which people sometimes add minus sphere back in when removing. The answer is yes. Minus cyl is just myopia that’s in one axis. If you remove it, the glasses may be too weak, so you add it back in as sphere (but usually only half the amount, because sphere acts in the perpendicular axis, too).

With plus sphere, you would have to add in plus power (or remove minus) to keep the same spherical equivalent. If you had -2.00 SPH +1.00 CYL x90, and you dropped the CYL, you’d be left with -2.00 SPH. Now let’s try the plus notation. -1.00 SPH -1.00 CYL x180 (or x0 - same thing). if you dropped the CYL, you’d be left with -1.00 SPH. Big difference.

Now let’s look at keeping spherical equivalent. Add half the CYL to the SPH and remove the CYL. -2.00 SPH +1.00 CYL x90 becomes -1.50 SPH. And the same for the plus notation. If you needed a bit extra power, you could just drop the minus cyl and go with -2.00 SPH. If you needed a bit less, and dropped the plus CYL, you’d have -1.00 SPH.

Lots of ways to lens the cat, and it would vary by person and situation. If you’re undercorrected to begin with, just dropping plus cyl and not doing anything else might be a good idea. If you’re overcorrected, it would be a bad idea.

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