Positive CYL conversion and prescription reduction

Prescription -2.0 CYL both eyes
which equals to -2.0 SPH/+2.0 CYL

Here is the QUESTION on lowering prescription
Do I add +.25 CYL to -2.0 CYL which equals = -1.75 CYL
OR
Do I subtract -.25 CYL from +2.0 CYL which equals = -2 SPH/+1.75CYL

PS: watched Ian squire, read forum, Jakes youtube regularly.

After a second reading of your post, do you mean you have 0.00D in both eyes and -2.00 CYL in both eyes?

Exactly. 0 SPH and -2 CYL. I can add prescription to the post later.

Wow. That’s very special, even here at EM I would say :astonished:
Axis suggests you have vertical double vision or ghosting without glasses.

If I were you I would choose one from the below options depending on what I can tolerate and how much the cyl disturbs me.

  • Keeping SPH zero and gradually reduce cyl by 0.25 or by 0.5 each time and alternating it with no glasses when it feels ok

  • Increasing SPH by half of the cyl dropped: -0.5D SPH and -1.00 cyl (aggressive version) or -0.25D SPH and -1.5 cyl (more cautious approach)

  • Cold turkey on glasses when possible / existing prescription when not and drop when the existing prescription already feels too much (this version may be super aggressive and may mess up your visual cortex too much due to high cyl value at the start)


Edit: all of these “next glasses options” I listed were meant with the original positive axis at 3 and at 10. And then wichever you opt for, pop it into the converter you found if you are ordering from a place that doesn’t deal with positive axis cyl.
Actually it’s no longer your eyes that are very unusual but your opto’s prescription :sweat_smile:


Which will work best for you? This is a totally complex area, a lot depends on lifestyle, lights condition, screentime, how much you got dependent on correcting cyl, etc…

Based on my readings your case is the one when it is worth playing around with a test lens kit instead of ordering glasses and try and fail.

And of course, all above is simply my brainstorming for my eyes if they had this prescription. You’ll need to make a decision for yourself considering what you have already learnt about your eyes and vision, and reactions to prescription changes.
Good luck!

This video is a bit difficult to listen to but describes a similar case (though starting from higher SPH higher cyl, but now at 20/20 with some remainder of cyl - very sensitive to bad lights.)

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I’m not an expert, but I guess that:
Prescription 0.0 SPH/ -2.0 CYL <your_angle>º
equals to -2.0 SPH/+2.0 CYL 180-<your_angle>º

As the part of the eye that needs the -2.0 diopters is directed to <your_angle>.

https://www.aclens.com/positive-cyl-converter
Axis is not a problem … problem is the way of reducing prescription …
Because
+.25 Cyl to -2.0 Cyl euqals to converted -1.75SPH/ -1.75 CYL
which is different from
-.25Cyl to -2.0SPH/ +2.0Cyl which equals to -2.0SPH/-1.75CYL

I understand what Jake says about not messing with prescription and change 1 thing at a time … but as you can see here we have a Scenario :slight_smile:

0.0 SPH/ -2.0 CYL <your_angle>º
equals to
-2.0 SPH/+2.0 CYL 180-<your_angle>º
(as it will also range from (-2.0+2.0 =) 0.0 to (-2.0+0.0 =) -2.0)

So, you can now reduce to either:
0.0 SPH/ -1.75 CYL <your_angle>º
or
-1.75 SPH/+1.75 CYL 180-<your_angle>º

1st is simpler, so why not just use it !?