Part II — Color Vision Deficiencies
Andy is a 35-year-old male. Much to the chagrin of his paternal grandmother, he has been color vision deficient all of his life. As a young child entering into kindergarten he was given the Ishihara pseudoisochromatic plate test, a common metric for testing color vision deficiencies. As he was shown the colored series of dots arranged in a circle, he would struggle to find the numbers he was told were there. Sometimes, even though he saw a number, the number he saw was different from what the test administrator was expecting. Other times, he could see numbers where others couldn’t see any. These results confirmed what his color vision deficient mother had known all along, that he too was color vision deficient. Growing up, his difficulties with color vision were ever present but generally didn’t affect his life; he could use all colors while coloring as long as the crayons were labeled, he wore solid color clothes that he knew the color of and he avoided the color purple. Still, there were some times that his color vision deficiencies made his life more difficult especially in determining whether bananas were ripe, ensuring that raw chicken was cooked fully and buying clothes for himself. He also firmly believed that the color purple was a figment of marketing rather than a color that was distinguishable from blue.
As he grew older, he noted that most color confusions mentioned by ‐red-green color blind‐ people didn’t seem to bother him as much as some others. He could easily distinguish the colors red and green whether in a match between two football teams, spotting an orange cone in a green field of grass or in other ‐common‐ confusions. Still, other color combinations were difficult for him. Despite knowing that his ability to see color was different from others, he had not known the extent, nor the specific colors that he was unable to see. To combat this, Andy took as many different color vision tests that he could in hopes that he could learn about the extent of his color vision deficiencies. Unfortunately, most of these tests were limited in their ability to differentiate between the varieties of color vision deficiency, and simply noted whether a deficiency existed or not.
Last year, he heard a story about a company that claimed to make glasses that could help colorblind people (for an example of a product see EnChroma, http://enchroma.com). It was alleged that when people affected by color vision deficiencies put on the glasses, they could suddenly see a variety of colors that they had never been able to see before. These ‐magical‐ glasses seemed to be able to transform the light coming into your eyes, intensifying some wavelengths that would allow the wearer to see many other colors than previously. Despite the promise of allowing him to see the infamous color purple, Andy was not willing to purchase the glasses on a whim, especially since there was a warning on the company’s website that the glasses may not work with all types of color vision deficiency. Curious about the possibility of fixing his color vision issues, he began to do more research and learned that the problems he was facing were likely more complex than not seeing red or green as he assumed.
Questions
3. What are the different types of color vision deficiency and how do they differ? What is the difference between the ‐opia‐ and ‐anomaly‐ versions of a condition? (Give an example if it helps to clarify your response.)
4. Why are protanopia and deuteranopia more common in males than females? Is it possible for females to be afflicted? Why or why not?
5. Why is tritanopia less common in the general population than the other forms of color vision deficiency? Are there different inheritance modes of tritanopia?
6. Since most forms of inherited color vision deficiency are recessive, postulate why color vision deficiencies would not have been reduced to the point of disappearance. Specifically, in what ways could color vision deficiencies be evolutionarily advantageous when compared to a population in which all people perceive the same colors?
7. Using your knowledge of absorbency of the cones how would someone affected by the different deficiencies perceive different colors? Which colors would possibly be confused?