Comments on: Colorblind Person Taking a Visual Acuity Test

By: Clive

Clive — Thu, 08 Jan 2009 01:11:30 +0000

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.

By: An optometrist

An optometrist — Sun, 12 Oct 2008 15:53:53 +0000

…..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)

By: An optometrist

An optometrist — Sun, 12 Oct 2008 15:44:46 +0000

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.

By: Michael Nash

Michael Nash — Fri, 14 Dec 2007 02:36:42 +0000

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.

By: Daniel Flueck

Daniel Flueck — Tue, 04 Dec 2007 20:13:39 +0000

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…