It’s that time of year again. Every fall, our local doctors of optometry, along with school nurses and a plethora of volunteers, corral students through our Lions Club’s Sight Savers trailer performing vision screening. And, every fall I have concerned parents rushing in their children to confirm if there is an eye problem. This year was no different.
Last week I entered my exam room to see a first grader who, it was determined, was color blind. Of course, his father did not believe the testing was correct and proceeded to confirm that his son new ALL of his colors and that there was NO WAY he could be color blind. I pulled out my trusty color vision test; administered the test to the son; and showed that indeed he was color deficient. On one page of the test with the number “35”, a color deficient person would only be able to see one digit. The boy proudly and confidently proclaimed that the number on the page was “5”. Even with prodding and cajoling from the father, his son could only see the number “5”.
A little physiology lesson:
In the retina, there are two types of nerves – cones that see color, and rods that see light. The cones are further differentiated in to three types – one that is stimulated by red light, one by green light and one by blue light. In order to have “normal” color vision, all three cones need to be present. If one of the cones is missing, or more commonly not as sensitive, then the person would have confusion of certain colors. This student has a deficient green cone. I explained this condition to the father and the student and how it would affect him.
If we have green paint and mix it with red paint, we make brown paint. (Green + Red = Brown)
If you cannot see the green, then red and brown look the same. (Green + Red = Brown)
If we mix green with blue, we make aqua. So, blue and aqua look the same. (Green + Blue = Aqua)
This confusion of colors is what is known as “color blindness” or more correctly “color deficiency”. I explained that it is important to let the teachers know so they do not grade down for improper answers, and discussed job restriction for color deficient people. The two most common job restrictions are law enforcement and commercial aviation. If a color deficient police officer was told a suspect has a brown coat on and stops someone with a red coat on, that just doesn’t work. I do have several patients who are pilots and are color deficient. They are able to get licensed to fly, but not to fly at night due to the need to differentiate the colored lights on airstrips – no commercial or airliner work.
Facts about color deficiencies:
- The gene for color deficiency is carried on the X chromosome
- Somewhere between 8 to 10 percent of the male population in the US is color deficient
- Less than one half percent of the female population in the US is color deficient
- Men cannot pass color deficiencies on to their sons; it passes through mothers who are carriers for the gene
- The incidence of color deficiency is highest in Caucasians; then Asians, then Hispanics, and lowest in African Americans
- Red-Green defects account for over 95 percent of color deficiencies
- Blue-yellow color blindnessis a dominant, not sex linked trait, which means both men and women are equally affected.
- John Dalton wrote the first known scientific paper (1794) regarding color blindness. He was color blind himself.
- Color deficient people hate to be asked “What color is this?”