Maybe you are thinking that all of color blind people see the world consisting of black and white only. But actually not, not all of the patients are suffered from total color blindness. In fact, the majority of them were suffer from partial color blindness. It means, they can still see colors, but not as complete as a normal person.
There are three types of partial color blindness: Deuteranopia, Protanopia and Tritanopia. Again, they, who are suffered from one of this type, could see colors too. However, for certain colors, they have difficulties in distinguishing them. For example, Protanopia and Deuteranopia have difficulties to distinguish green from red colors, that’s why these types of color blindness are also called as red-green defficiency or red-green color blindness. Whereas, Tritanopia has difficulties to distinguish colors in bluish color spectrum.
All of them are caused by the lackness of one of three cone cells. Cone cells are responsible to absorb lights and activate color pigments. In normal conditions, eye’s retina contains all of three cones. They are S-cones, M-cones and L-cones, they are also reffered to Blue- Cones, Green-Cones and Red-Cones respectively. To see colors completely, we need all of those cones presences to work together. They process color information captured by retina and then this information will be sent to brain to be perceived. The lackness of three types of cone cells, even only one cell, results incomplete color information for brain. This condition of lackness often called as color blindness.
This article will not reveal about how and the cause of color blindness in detail. Because it will need so many technically words and phrase. We are talking about how color blindness perceive colors. What is the difference between colorblind and normal color perception? Why are they cannot pass the Ishihara test, which is the common test for color blindness. We need a simulation to understand colorblindness color perception.
These are the simulation:
Simulation 1. Rainbow Colors
We can see that color blindness could see colors, could’nt they? But the simulation reveals that color blind perception of colorblindness’ are differ to that of normal color vision. We can see Deuteranop and Protanop color perceptions are almost similar to each other, their color spectrum is only consists of two colors: red and green. Deuteranop and Protanop will perceive Yellow, Green and Red color to yellowish color, which are differ only in brightness. Whereas, blue colors are not affected very much, they are still blue.
For Tritanop, who is lack of S-cone or Blue-Cones, confuse blue with green and yellow with violet.
Simulation 2, Color of Pencils
What is the Ishihara test?
Ishihara Test is a common test for assessing color defficiency to human. This test is ivented by Dr. Shinobu Ishihara, a professor at the University of Tokyo, this test is published in 1917. This test will show people to a number of colored test. Each plate contain a circle of colored dots. The dots form a number or pattern which is visible to normal color vision and is difficult to see for the people who are suffered to color vision defect.
This simulation below shows one of Ishihara Plates. Normal Color Vision will show a number of 6, so does the Tritanope. If people is tested by this plate and do not recognize any number on it, it means there is likely the person is suffering from one of red-green colorblindness, Protanopia or Deuteranopia.