Monday, December 24, 2007

How To Assess Colorblindness

Quick site update: I installed Photoshop this past week and started playing around with it. Heh, probably not the best software for the colorblind. Anyway, check out the new logo up top!

When I was on Family Medicine, my preceptor was involved with clearing people medically before they could fly. Usually it was fairly routine, but the one thing that differed from the typical physical is that he had to scrutinize their eyesight much much more than usual. One of the items he had to check was their color vision and make sure they were not colorblind.

There are several ways to do this, but the most popular method involves the Ishihara Color Test. We have all seen these before. They are basically dots of different sizes and colors that form a number that is visible only to people who are not colorblind. Here is an example (do you see a number below?):

Can you see the '74' in the middle in green dots? If not, that might mean you're colorblind (or illiterate, I suppose). The reason the dots are red and green is that this is the most common form of colorblindness with up to 10% of males having this disability. I mention 'males' because the gene for the red and green receptors are on the X chromosome, which means the inheritance is X-linked. There other forms of colorblindness like blue-yellow colorblindness, but this has autosomal inheritance and is less common.

However, even after one has diagnosed a patient, it is interesting to consider how they see the world. A colorblind person went ahead and tried to demonstrate through photographs, which I found interesting. I wonder though, when making the page, didn't the images look identical to him since he couldn't actually see the full color images like most of us can? How does he know he did it right? I guess there really no way to see the world exactly as he does, but it's still an intriguing approximation.

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