Overcorrection and True Myopia Value

New and excited to be here and embark on this journey.
I did do a search on this topic but didn’t find the exact conversation I was looking for.

I just did the prescription lens check and blown away by what came back…

R = 4.5
L = 5.5

I was just prescribed for glasses on Monday
R = 6.0
L = 8.0!

I tried the contact lenses she prescribed at 6.0 for each eye because I do mono-vision lenses. I can see very clearly, there is no blur.

Can they really be that off and over-prescribed? She was the first one to warn me I was entering high myopia. I was a little depressed when she told me because no other eye doctor warned me that I was close to high myopia. No one talked to me about prevention. Even she didn’t really know what to tell me other than to eat right and exercise. Which I pretty much already do.

So, does this mean that my myopia isn’t as bad as they are telling me?

I just ordered my new normalized based on these readings.
We’ll see how I did when they get here. Very excited!

Thank you!


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I think so! One potential problem is that when optometrist does a refraction they ask “which looks better, 1 or 2” and a lot of people like minus. To avoid over-correcting they need to make sure that you can actually read an additional line or two on the eye chart before they give you more minus. I saw one professor describe additional minus power should be treated like money, you don’t freely give it out, you have to get something in return (being able to read another line on the eye chart.) It’s possible when they performed the refraction you thought -5 looked better than -4, and -6 looked better than -5, even though you couldn’t actually see better with -6 than -4. The text probably looked a little smaller and darker or cleaner, but all that extra correction didn’t actually “buy” you improved vision.

You can try the duochrome test yourself with your glasses and see if you are over or under-corrected.

If the green side looks clearer and the red is blurry, you have too much minus. If the they look the same that’s “full correction”. If the green is blurry and the red is clear you have too much plus for full correction, which might be OK for your normalized.

It’s possible they could have given you such a large over-correction, certainly.


Can I ask why the red would be blurry in case of overcorrection?


Because of physics I believe. Different wavelengths of light are refracted differently in the eye, either a bit in front or a bit behind the retina.


This is interesting! I wonder why no optician has ever performed that test with me…
I sometimes wondered in the past why I would see green traffic lights clearer than red ones with my glasses. I always assumed it was because different wavelengths are refracted slightly different, so I’m happy so see I was right about that. What I didn’t know though is that blurry red means I was over corrected. :frowning: I do remember seeing some red and green things at the optometrist on the eye chart projector, but they were never used or talked about…


This is really helpful and makes a lot of sense. Thank you!
Does this work with contact lenses too? I have a sample pair of 6.0 she gave me.

I am not filling my new eye glass script. I ordered glasses based on the End Myopia calculator. They don’t arrive until May 20. I am using my old 4.25 contact lenses for computer and day time. But I do know I need something higher for night and long distance driving which I don’t do very often. I will save the 6.0 for those moments.
Hopefully, I will never need them.

Update: I just tried it with the -6.0 contacts and both sides look pretty clear :frowning:
There is a little blur with my -4.25.

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You’re almost certainly using a lot of accommodation with the -6.0 contacts if you can see it with a little blur with the -4.25 contacts. By that I mean that your cilliary muscle has to contract to bring the screen into focus which is what you don’t want (that’s what causes cillary spasm leading to psuedomyopia and myopia.)

It should work with contacts. You have to get far enough away from the screen that you’re at “distance” and you’ll probably want to be in a dark room, if you have the screen up close with no blur they’ll look the same. It takes a little playing around with to get the effect or see how it’s supposed to work.


Just to be clear on what you are saying.
The 6.0 are causing the ciliary spasm. Not the 4.25,

Thanks so much for all your help!

I just retested in a dark room at a distance…and it’s still pretty clear in both eyes :frowning:

Maybe, I need to go up from a 4.25?

If you can see OK with your -4.25 contacts (OK meaning better than 20/40) I would wear those instead of the -6’s most of the time.

If I understand you correctly, when you self-measure you get R = -4.5, L = -5.5, so if you’re wearing -6 contacts your right eye has to accommodate 1.5D to give you clear vision at distance, and your left eye has to accommodate 0.5D at distance, which means the cilliary muscle is working all the time even when you’re looking off into the distance. And if you’re looking at something closer than 20 feet away (like your phone or computer) then your eyes have to accommodate even harder, probably to their maximum, which creates cilliary spasm.

If you have access to lower-powered contacts, glasses, or trial lenses, I’d be curious to see how those work for you, -4.25 sounds good for your right eye, but that’s a big under-correction if your left eye is at -5.5 (reasonable for doing near work though).

I think when you’re trying the duochrome test with the -6 contacts your eyes are accommodating a lot, so they’re bringing you to your “full correction” by having to contract the cilliary muscle, which isn’t what you want. [With your right eye you’re looking through -6D of contact lens +1.5 accommodation of your own lens=-4.5D full correction.]

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So if we tell the optometrist that the green is clearer, would he reduce the minus a bit?

Probably, but I wouldn’t bother lying to the optometrist, it’s much easier to just be honest and order your own glasses or contacts with the prescription that works best for your purposes.


Really, thank you again for all your help. Everything you are saying is really helping find the correct Normalized and Differentials for me.

I spent today walking and driving to re-evaluate everything. And came back home trying different lenses on. I only have -4.25, -5.50, and my new -6.0 samples on hand. I check all my old travel bags for lower old scripts but nothing. Something huge I forgot to mention, that I’m so sorry about. I completely forgot, I do monovision. So, my left eye is under corrected on purpose. What I didn’t realize until today, is how bad my left eye is. The -4.25 is not nearly strong enough to challenge blur. It’s just blurry. I tested with -5.50s and the -6.0 contacts, and it was still kind of blurry :confused:

I could probably go up to -6.50 in my left eye and still have a little blur. While my left eye doesn’t like any of the lenses. My right eye is my dominant eye and seems to like everything, 4.25, 5.50. I saw one of Jake’s videos where he said if the weaker eye is not challenged it will let the dominant eye do all of the work.

So here is what I am going to do now. It’s pretty close to True Myopic calculator for my close up which was R: -4.5, L: -5.5. I realized the calculator is for close up and you have to add for distance.

Close up Differentials
These are contact lens measurements.
I was doing -4.25 in both eyes for close up before we spoke. This feels much better.
I can see but there’s still a little bit of challenge in both eyes separately but together they see well. I could probably go down .25 in each eye too.
R: -4.25
L. -5.50

R: -5.50
L: I’m kind of stumped. I am may need a 6.50 :confused:
You can’t do mono vision with active focus.

Original Prescription
Glasses Contacts
R: -6.0 R: -6.0
L: -8.0 L: -6.0 (mono vision)

So this makes sense now.

Sorry, again about forgetting about the monovision and if this is more information than you wanted to know, but it helped me writing it all down.

Thank you again for all your help in helping this newbie figure things out!

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