Sep 29th 11 Posted by Randy in Web Design

Color Blindness & Leprosy Revisited

The connection between color blindness and leprosy I found and blogged about several days ago was so bizarre I had to investigate. The only reference to clinical research I could find on the subject was this page from PubMed:

Indian J Lepr. 1992 Oct-Dec;64(4):483-6.

Prevalence of colour blindness among patients with leprosy.

Shwe T.

Clinical Research Unit (Malaria), Department of Medical Research, Dagon, Yangon, Myanmar.

Using Ishihara test plates the prevalence of colour blindness was studied on six hundred and ninety-seven leprosy patients and two hundred and ninety-two normal healthy controls. 7.88% of male patients with tuberculoid leprosy, 12.18% of male patients with lepromatous leprosy, and 0.67% of male controls were detected to be colour blind (red-green deficiency or total colour weakness). The differences between the different groups are significant. Among female patients and controls, only one lepromatous leprosy patient was detected to have red-green deficiency. This suggests the possibility of a genetic predisposition to Mycobacterium leprae infection in patients with leprosy.

When I saw the numbers, my first reaction was, “This study is flawed. The number of color blind controls is way off.” After I thought about it for a moment, I realized the number of color blind male controls, 0.67%, is a typo. The number should be 6.7% (or 0.67). The percentage of color blind males is often reported to be 8.1%. In the study cited above, not all color blind males are part of the control group. The 1% with blue-yellow deficiency is not included. Hence, 6.7% sounds like a reasonable number.

What the researchers have reported is that a higher percentage of leprosy victims are color blind. To conclude that color blindness causes leprosy is wrong. Logically, it must be the other way around; leprosy causes color blindness. Color blindness impedes a person’s ability to see things. It does not cause disease. I’m sure we will all sleep better now that that’s been cleared up.