Colorblind Person Taking a Visual Acuity Test

I need a new pair of glasses and therefor I went to visit the optometrist to test my eyesight. Just before I shook hands with the optometrist I told my wife, that they are always using those tests with a red and a green half, differing in acuity and my color blindness doesn’t let me name them 100% accurate.

Usually the optometrist asks, if the acuity of red or the green half is better and I answer with left or right just because I’m not sure if I pick the right color name. This time it was even better. After a few tests…

Optometrist: You’ll see a red and a green part.
Me: I’m colorblind.
Optometrist: Oh, doesn’t matter. Just tell me which side is better for your eyes.
Me: I can’t really see the red one.
Optometrist: Doesn’t matter. Just tell me.
Me: Green on the right.
Optometrist: Ok. — And now?
Me: The red has no contrast for me. I can’t really see it.
Optometrist: We will see. Which is better for you?
Me: Green again.
Optometrist: And now?
Me: Green. I can’t see the red. And green doesn’t look sharp at all.
Optometrist: Hmm. — What about this?
Me: Green. But very bad.
Optometrist: Ok. We will switch to another test.

She changed the test to another one which was no problem for me. But after a short while she switched back again to the red and green halves.

Optometrist: Can you see this?
Me: Not really.
Optometrist: Which is better?
Me: Green again. But I can’t see the red.
Optometrist: Ok. — And this?
Me: Green, but very blurry. There is no contrast on the red side.
Optometrist: Well, doesn’t really matter. We go on from here.

Finally. – Finally she understood that I can’t see any contrast on the red side because of my color blindness. It was just impossible for me to compare those two parts.

Only after the test I really realized, how crazy this must have sound to the optometrist. Maybe she encountered the first time someone like me with a strong red-blindness. How strange to hear that someone can’t see although he can see.

But I ask myself, why do they still have those tests in use. Shouldn’t they have learned in the last years? I suppose those tests easily could be switched to another color which is much better visible for us red-blind guys. — Dear optometrists, change your test setup taking also color blindness into account.

6 responses on “Colorblind Person Taking a Visual Acuity Test”

Ling December 4, 2007 at 3:53 pm

Hi. I am from Singapore and I just happened to bump into your web. I have to disagree with you about the optometrist part because I ,myself , will be graduating with a Diploma in Optometry in the near future. The red-green chart, often referred to as Duochrome Chart, helps refining the best vision sphere (which is the prescription we’re giving you). This is performed so that the spectacles given would not be over or under corrected. While doing that test, what you are supposed to see is the black letters against the green/red coloured background, so it does not really matter if you’re colour-defective or not. All you have to do is just to compare the letters on both side, and decide which letters appear darker and sharper, instead of judging it against the background itself.

Daniel Flueck Post authorDecember 4, 2007 at 9:13 pm

Ling, thank you very much for your contribution. I suppose you are not colorblind yourself :-)

I just wrote down what happened to me and nothing else. I’m severely red-blind and definitely couldn’t spot the black letter on the red background.

For red-blind persons, red looks much darker. So it blurs with the black letter which makes it not to judge against the other green letter.

Believe me, I really couldn’t see the letter…

Michael Nash December 14, 2007 at 3:36 am

I think that the optometrist is really missing the point. To someone with a strong red deficiency, the black letters on a red background are black letters on a black background, and the black letters on the green background are like black letters on a dark background. It has nothing to do with the sides, so would be of no use (as far as I can tell) in a test to balance the prescription of glasses in the left-right plane.

An optometrist October 12, 2008 at 4:44 pm

The duochrome test work perfectly well with even the most severely colour blind patients. The optometrist is asking you to make a blur discrimination judgement. Eg ‘Are the circles/letters clearer/sharper on the red side or the green side’. You are NOT being asked to make a colour discrimination judgement. To a protanope (someone with no ability to detect red) the red half of the target will appear very dull, so the optometrist should modify the question to one of ‘are the circles/letters clearer on the top or bottom/left or right side of the picture?’ There is no reason why your couldn’t make this judgement unless you fell into the category of those unable to make comparative judgements. These people tend to think there is a ‘correct’ answer to the question or that the optometrist is playing some curel joke.

It sounds like you could have had better instructions from your optometrist but there is no reason for her to avoid this test on the basis of your colour vision defect.

An optometrist October 12, 2008 at 4:53 pm

…..In fact, even if you could not detect any letters/colours on the red side you can still use the amount of blur on the outside of the target itself (e.g. the edges of the red/green rectangle) which will be as blurred/clear as the letters/circles within them. Again, good instructions form your optometrist would help here.

(e.g. http://www.perret-optic.ch/optometrie/test_vision_pres/opto_tes_pres_image/test_duochrome.gif)

Clive January 8, 2009 at 2:11 am

I had reason to visit the opticians recently and had to do a peripheral vision test. This involved following a red dot as moved around a brightly lit background.

Too often I lost the thing I was supposed to be looking at (the backboard was white but cast in shadow and since red looks a nondescript slate grey to me, it just vanished.

I protested that I only looked where I thought I needed to when I saw something move not because I could see what I was supposed to be looking for.

and again, unhappy to report that odd paradoxical feeling of eye-specialists being essentially uninterested in your own perceived ability of your vision to meet the criteria of the test.

I recognise also the contrast panel with the letters on red and green backdrops and the problems for me of trying to pick out black text on a red background.

Again: my protests availed me naught.

Ling December 4, 2007 at 3:53 pm

Hi. I am from Singapore and I just happened to bump into your web. I have to disagree with you about the optometrist part because I ,myself , will be graduating with a Diploma in Optometry in the near future. The red-green chart, often referred to as Duochrome Chart, helps refining the best vision sphere (which is the prescription we’re giving you). This is performed so that the spectacles given would not be over or under corrected. While doing that test, what you are supposed to see is the black letters against the green/red coloured background, so it does not really matter if you’re colour-defective or not. All you have to do is just to compare the letters on both side, and decide which letters appear darker and sharper, instead of judging it against the background itself.
Daniel Flueck Post authorDecember 4, 2007 at 9:13 pm

Ling, thank you very much for your contribution. I suppose you are not colorblind yourself :-)

I just wrote down what happened to me and nothing else. I’m severely red-blind and definitely couldn’t spot the black letter on the red background.

For red-blind persons, red looks much darker. So it blurs with the black letter which makes it not to judge against the other green letter.

Believe me, I really couldn’t see the letter…
Michael Nash December 14, 2007 at 3:36 am

I think that the optometrist is really missing the point. To someone with a strong red deficiency, the black letters on a red background are black letters on a black background, and the black letters on the green background are like black letters on a dark background. It has nothing to do with the sides, so would be of no use (as far as I can tell) in a test to balance the prescription of glasses in the left-right plane.
An optometrist October 12, 2008 at 4:44 pm

The duochrome test work perfectly well with even the most severely colour blind patients. The optometrist is asking you to make a blur discrimination judgement. Eg ‘Are the circles/letters clearer/sharper on the red side or the green side’. You are NOT being asked to make a colour discrimination judgement. To a protanope (someone with no ability to detect red) the red half of the target will appear very dull, so the optometrist should modify the question to one of ‘are the circles/letters clearer on the top or bottom/left or right side of the picture?’ There is no reason why your couldn’t make this judgement unless you fell into the category of those unable to make comparative judgements. These people tend to think there is a ‘correct’ answer to the question or that the optometrist is playing some curel joke.

It sounds like you could have had better instructions from your optometrist but there is no reason for her to avoid this test on the basis of your colour vision defect.
An optometrist October 12, 2008 at 4:53 pm

…..In fact, even if you could not detect any letters/colours on the red side you can still use the amount of blur on the outside of the target itself (e.g. the edges of the red/green rectangle) which will be as blurred/clear as the letters/circles within them. Again, good instructions form your optometrist would help here.

(e.g. http://www.perret-optic.ch/optometrie/test_vision_pres/opto_tes_pres_image/test_duochrome.gif)
Clive January 8, 2009 at 2:11 am

I had reason to visit the opticians recently and had to do a peripheral vision test. This involved following a red dot as moved around a brightly lit background.

Too often I lost the thing I was supposed to be looking at (the backboard was white but cast in shadow and since red looks a nondescript slate grey to me, it just vanished.

I protested that I only looked where I thought I needed to when I saw something move not because I could see what I was supposed to be looking for.

and again, unhappy to report that odd paradoxical feeling of eye-specialists being essentially uninterested in your own perceived ability of your vision to meet the criteria of the test.

I recognise also the contrast panel with the letters on red and green backdrops and the problems for me of trying to pick out black text on a red background.

Again: my protests availed me naught.