How do I handle big diopter differences in my eyes?

Hi everyone,

I’m at the beginning of my EM journey. Already got my overcorrected glasses reduced so I can see 20/20 with them and got my first differentials, so far so good. When reading a little more about EM, I began to wonder how I should handle the diopter difference in my eyes. It’s -2 to -2,25 diopters (my right eye is the stronger one). Do I even need to worry about this in the beginning?

Thanks for your help!

I wouldn’t worry about it at the beginning. As your eyes improve you can try to make the gap a little smaller, but right now the main things are keeping the computer and reading at the edge of blur (as far away as you can without it getting blurry), and increasing your outdoor time and paying attention to as much detail as you can outdoors. Try to focus on every sign, license plate, leaves on trees, birds and squirrels, boats on the water, whatever there is to look out outdoors. Get outside as much as you can.

[In case I’ve misunderstood and you’re saying your current prescription is Right Eye is -2 and Left Eye is -2.25]

If you’re saying there is only a 0.25 D difference in your eyes I would just keep the lenses in front of them the same. For example, you could use -1.75 D in each eye for your normalized (distance) glasses and use -0.5 (or even zero correction) for viewing the computer.

Try to avoid putting -0.75 in one eye and -0.5 in the other.

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-0.25 D difference is BIG??? what would be a small diopter difference for you? something smaller than the smallest increment they normally manufacture? :smiley:

anyhow Jake recommends handling equalisation at the end

and also 0.25 D is not significant, don’t worry about it

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I think she’s saying the DIFFERENCE between the eyes is 2 to 2.25 diopters. Like maybe she’s -5 in one eye and -3 in the other or -2.75 (or -10 and -12) … but the way the question was asked made it a bit tricky.

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Oops Well anyway people should find Jake’s blog post on prescription complexity. Equalise at the end


Sorry, I should have explained better. As @nycmao said, I meant that the difference between my eyes is 2 to 2,25 diopters. My full prescription glasses are -2,25 on the right and -4,5 on the left. My differentials are -0,5 on the right and -2,5 on the left.

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Baby steps. You are on the right track just getting that basic first step. You can measure yourself each eye and gauge how much of that gap is strictly needed as you get to know your eyes. Certainly read up on equalizing before trying to tackle it. And maybe tuck this away for furture reference: Tag-In Method - YouTube


The general advice is to have the same sph drops from both eyes a few times to get the hang of it and then have a single eye 0.25D sph drop and rinse and repeat. However, when the gap equals the lower diopter value as in your case, I think it is totally up to you how and when you tackle the gap part.
I’d say the most important is to establish how much the real gap is without the opto overcorrection. You may find that it is not 2.25D but just 1.75D. Make sure this doesn’t increase during the drops, i.e. you don’t let your right eye run ahead leaving the left eye completely behind and end up with zero and -4.5D.

You can try equalising in between standard drops but I guess it will be a learning curve to understand if your left eye is switching off and needs ‘re-activation’ or the left eye participates in the party if given enough corrections.
You may want to get to 0 and -2D (or -1.75D) with your differentials before seriously targeting the gap reduction. I’d keep diffs and norms with the same gap first and later maybe I’d have a 0.25D less gap in diffs then in norms.

Currently there seems to be a trend with optos sometimes actually encourage having one eye with good vision for distance and one eye with good vision for close up. I wouldn’t encourage teaching this to semi equal eyes as the optos do as it is quite taxing on the brain, but when this is the initial set up anyway you might want to take some advantages from it? Equalising is often a game of patience.

I believe you’ll have a unique journey. :unicorn: Good luck.


Thanks for your help! I measured my eyes with the EM App again and the results were -1,7 on the right and -3,8 on the left. I also put up a Snellen chart and I can still read 20/15 with my full prescription glasses and both eyes. The 20/20 line is tinily blurry with just the left eye and with the right eye I can still see 20/15 very clearly, so I guess my right eye is for sure still overcorrected. I think when I’ll get my normalised, I’ll drop -0,5 on the right and -0,25 on the left to get rid of the overcorrection. I decided that I’ll tackle equalising after I’ve done my first or second reduction; it just makes more sense. I feel like equalising is still too difficult for me at the moment.


Thanks for your detailed answer :slight_smile:
As I already said in my previous answer, I put up a Snellen chart and I can still read 20/15 with both eyes, so I’m still overcorrected… With the right eye only, I can still read 20/15. With the left eye only, the 20/20 line is very tinily blurry, so I guess the prescription for the left eye is fine, but the right one is definitely still overcorrected. I guess I could do with -2,0 or even -1,75 as you mentioned.
I plan to buy my first normalised at the begining of July because I still need to get used to my differentials (but they already work well for me). But I’m wondering whether I should just drop 0,25 diopters from my full prescription glasses (because that is what the Wiki and everyone else recommends) or if I sould drop 0,5 from the right and 0,25 from the left since my right eye is still overcorrected… anyway, I still have some time to make that decision.
But I know I only want to try equalising when I’ve done my first or second reduction. It’s still too challenging at the moment and I need to get the hang of other things before I start equalising.

I think this is a great call eliminating the over correction now and not taking on any more till you get a handle on things. Quick note be sure when you change the ratio that you get diffs to match. So when you eliminate the .5 on the side that is over corrected, knock out another .25 on that side for your diffs.


If it is right eye 20/15 and left eye 20/20 with tiny blur then I would avoid increasing the gap by all means and I would go for the same drop in both eyes. Just my opinion.