Duochrome test: Green and red light have a different wavelength

With a Duochrome test an optometrist checks the trial lenses.


So if the patient would say the GREEN is better the lenses given is more likely to be the one desired by endmyopia?

Another video similar to the one above.

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The patient would like to see green better so the diopters would be reduced. But then it has to end with red being better, or it’s overcorrected. I remember my eye test, where I couldn’t tell the difference between the letters on the colors and the optician said that’s not possible. It’s not always so clear.

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If you see green better (i.e. red is more blurrier) you are overcorrected.
If you see red better (i.e. green is blurrier) you are slightly undercorrected
If both red and green are the same, then this means that you reached the circle of least confusion.
If you see clearly at this point then this is a good prescription for full correction for the current lighting conditions.
If you dont see clearly you might have astigmatism.

When you are wearing your normalized or differentials, you should see red a little better than green, because you should be slightly undercorrected.

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Been reading about the Duochrome test and it brings up several thoughts about leveraging chromatic aberration.

  • To maximize focus stimulus without introducing blur adaption, would you want to measure your cm with a duochrome chart, and aim for the red side being clear and the green a little fuzzy? This should improve the precision of the measurement, and provide a quarter diopter nudge. When the green side is clearer you’re ready to move +0.25D.
  • The difference between the red and green side is a half a diopter, which is similar to normal eye dominance difference. Is our body intentionally keeping the lens correction imbalanced so it can get a clear red and a clear green image to combine in the visual cortex? Is balancing that last half diopter of difference between the eyes actually beneficial to binocular visual acuity and not just monocular visual acuity?
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I really like your second point, and have pondered the same.

@Varakari’s tool does exactly that :slight_smile: It provides a measurement image with both green and red text:

The difference between the red and green side is a half a diopter, which is similar to normal eye dominance difference. Is our body intentionally keeping the lens correction imbalanced so it can get a clear red and a clear green image to combine in the visual cortex?

It would explain why can you better with the combined vision of the two eye than with either one on its own. Also @jakey’s wisdom of use binocular vision and don’t really do patching (frequently and for too long) would get some confirmation.

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So, how well does the visual cortex deal with you switching your green and red eyes with lenses? Is it important to maintain that difference?

Sorry, but I understand your question. What you have in the tool is an image with both red and green text next to each other. When you want to measure your cm you go as close as needed to make both text sharp, and starts backing up. When the green one gets blurry, you can check that the red is still clear (so you’ve not backed up too much). There is no switching involving.

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At the end of the video posted above, it says that the duochrome test is not used for people with vision worse than 20/30, so it does not seem very useful for most of us.

They talking about using as a colored Snellen chart without glasses. Which of course is not useful, but that does not mean using different colored (or background) texts cannot be helpful.

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Good points. First point : use Varakaris vision log tool from the tools section of the forum, he has a red and green image to measure on. It’s what I do

It is useful for setting up the last part of your prescription, fine tuning. In the UK they always used it on me

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why not reduce the complication and just do cm measurements on a B/W snellen chart?

Because it’s not very accurate…

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I find the cm measurement tool on the program with magenta and turquoise ring more confusing to use, and I can’t seem to get a consistent measurement as compared to B/W printed text.

I don’t use the rings, just the text. And the text colors made it easier for me, not more complicated.
But of course it’s subjective, it the bw text works for you and you get stable measurements with them, then no need to use something else.

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I think that’s corrected acuity, because I’ve definitely had the doctor use this on me.

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(If you have vision deficit other than refraction error, or the doc can’t dial in within a quarter diopter, then both images will be fuzzy no matter how good or bad the refraction is.)

Thanks. I vaguely remember some green and red testing, but very many years ago, and I was certainly already more myopic than 20/30 then.

I guess I’m lucky that as myopic as I am in almost fully correctable. (Although I hate that term, its compensation, not correction.)

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