Can directional blur be caused by overprescribed CYL correction?

If CYL is over prescribed, can that cause directional blur as well? I have a feeling my CYL is over prescribed and intend to talk the eye doc down a little in few days, but I am seeing some directional blur in one eye. Does that HAVE to mean the CYL is too low, or could it be too high (he gave me glasses with less CYL correction than I had been using last)? If the SPH is too low will it make existing directional blur more apparent?

When you do have CYL lowered just right, how much directional blur will there be?

For sure. Correct cylinder correction = no directional blur.


Rena are you measuring it yourself? It takes work but once you get good at it that will give you ll the information you need.

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I tried once, but couldn’t figure it out. I may try again, I guess. My main goal in life is to have everything a little underprescribed just to eliminate headaches, and then any gains I make is a wonderful plus.

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Jake - I think I want some directional blur to make sure the CYL is a little low (keep headaches to the minimum in any case, and that’s the next thing I’m reducing as one eye is already at 0 SPH), but I think the directional blur I currently have is from too much correction - is that a possible side effect of too much cylinder correction, or am I horribly wrong?

What Jake says about correct CYL = no blur. I like to use his astigmatism tool that shows axis. I rotate that around and see if or where it blurs with correction. Then I experiment with astig lenses until it’s clear all the way around. Then I go down .025 CYL for a blur horizon effect. Seems to be working for me. Down from -1.25 to -0.50 in one year.


It sounds like you have tools that I don’t have. :smiley: Has blur with correction ever been due to too much astigmatism correction, or is it always a lack of astigmatism correction?

Very interesting! I wondered this too. Just recently printed out the astigmatism tool, gotta assemble it soon.

@Rena Both under- and overcorrection of CYL (or specifying the Axis wrongly) can lead to directional blur.


Here’s the astig msr tools page:

Also do a Google search on astigmatism measuring tools and you’ll find lots to work with. What works best for me is an L shaped right angle double or triple line. When astig is wrong one line will blur while the other is clear. When correct both angles are clear. Rotate around in a circle and see what changes. That’s how you discern axis.

Too much astigmatism correction will cause blur too. That’s why those tools I shared with you are so useful. Helps you see when it’s just right, not enough, or too much correction.

@ryanO_O Thankyou for confirming!

@dsweet440 The part I’m wondering about is how you experiment with different astigmatism lenses. Do you have some kind of kit, or just a ton of glasses??


No worries. It is worth pointing out that just as our myopia can fluctuate during the course of the day, our (nett) astigmatism <CYL, Axis> also varies throughout the day.

I have a test lens kit. Highly recommend them! And yes I also have a ton of different glasses…Most are too strong now :slight_smile:

Where do you get a test lens kit?

Ebay and Amazon. Big selection to choose from.

O_O that’s a little pricey

well if your myopia is not too high, you could go to Zenni, order their cheapest frames (7$ each) with something like -0.25, -0.50, -1.00, -2.00, -3.00 for spherical, and incremental values for whatever astigmatism you have (make sure to use the right angle).
You could order them double to have one for each eye.
Then you remove the lenses from the frame, you label them with a marker, and voilĂ , you got yourself a DIY test kit.