Parts of the thalamus and the visual cortex in the brain are involved in "seeing", also seeing colors. Color blindness can therefore also result if these areas of the brain, the optic nerve or the retina have been damaged. These types of color blindness usually happen because of an accident. They are not inherited. Inherited forms of color blindness affect the retina only.
That way it is possible that only a part of the visual field is affected by color blindness, but in the rest, there is no color blindness.
Some types of color blindness, but not inherited color blindness, can be cured.
There are several different problems that can cause color blindness.
This condition is very rare. People who suffer from it can only see in black, gray and white: They can perceive only differences in "brightness" and do not see "color". This is called "monochromacy".
There are two main types of total color blindness:
There are two kinds of red-green color blindness: protanopia or deuteranopia. Deuteranopia is the most common form of color blindness; between five and ten percent of males suffer from it. It is called Daltonism because John Dalton discovered it. Those affected have trouble telling the difference between red and green. As seen by protanopes (people suffering from protanopia), red is darkened. Most often, this is because they lack the receptors for long (protanopia) or medium (deuteranopia)-length light waves or because these receptors have changed their sensitivity.
Although the name is blue-yellow color blindness (tritanopia), people affected by this type of color blindness can usually tell the difference between blue and yellow. Instead they cannot tell the difference between blue and green, and also yellow and violet. It is different from the other types of color blindness because it is not linked to sex. It is equally possible for anyone to develop blue-yellow color blindness. It is caused by having few or no cones in the retina which can sense short wavelength light.
Sometimes, people do not have problems seeing color, but their brain has trouble "telling" the color, and interprets it wrong. It is also possible that only certain parts of the eye have color blindness; people may become color blind because of other diseases, but after the disease goes away, see normally again. This seems to be the case with certain forms of migraine.
Males have one X and one Y chromosome; females have two X chromosomes. Many of the genes involved in making color vision work are on the X chromosome: they are sex linked. For this reason, men are more often affected by color blindness than women.
The "color blind" gene allows non-color blind people see the difference between red and green. The gene is located on the X chromosome. This means that a male will be color blind if the single X he inherits from his mother contains the color blind version of the "color blind" gene. A female will inherit color blindness only if she inherits two X chromosomes containing defective (mutant) color gene alleles. In other words, a female needs to inherit "color blind" genes from both parents in order to be color blind.
The Ishihara plate test has been in use since 1917. Each plate has an image with dots of different size and color. People will then "see" different images (most often Arabic numbers). Those with certain types of color blindness will see different numbers from those not affected by color blindness.
Because many young children have not learned numbers yet, other tests have been developed. They use symbols, like a square, a circle or a car instead of numbers.
A color code is when there is much information in the color of certain item. Such codes cannot be understood easily by those who are color blind. For this reason, color should not be used alone to give information. Good graphic design avoids using color coding or color differences alone to give information. This does not only help color blind people, but also normally sighted people.
Cascading Style Sheets can be used on web pages. They allow to give a different color scheme for color blind people. Certain color scheme generators help graphic designers see color schemes as eight types of color blind people see them.
Color blindness is very sensitive to changes in material. A red-green color blind person may be unable to see the difference between colors on a map printed on paper. The same map on a computer screen or television may appear normally. In addition, some color blind people find it easier to tell the difference between colors on artificial materials, such as plastic or in acrylic paints, than on natural materials, such as paper or wood. Thirdly, for some color blind people, color can only be distinguished if there is enough color: thin lines might appear black, but a thicker line of the same color can be seen in the correct color.
In certain cases when it is important to understand information very quickly, the visual system may drop the colors, and only work in shades of gray. This is important to know when designing the interfaces for objects that need to be used in an emergency situation, like emergency brakes, or emergency telephones.
Because color blind people may not see the difference between colors such as red and green, some countries, such as Romania have refused to give them driving licenses. In Romania, people have started to change the laws so that color blind people will also be able to drive legally.
In the United Kingdom, electricity wires in houses used to be red, black and green. They were changed to brown, blue and green/yellow to help color blind people see the difference between the "live" and "earth" wires.
Many people do not understand color blindness. People who are color blind never swap the colors they are blind to. They may have trouble telling two colors from one another. That way they may have a problem finding the right kind of apple in the supermarket. The image below first shows the way that two apples look to a person with normal vision, and then the way it looks to a person with red-green color blindness. The left apple is a "Braeburn"; it is red in color. The apple on the right is a "Granny Smith"; it is green. To someone with red-green blindness, the apples look like they are almost the same color.
Sopron
Sopron ( ]; , ; Central Bavarian: "Ednburg", ) is a city of Hungary, near the western border of Hungary with Austria, at the foot of the Alps, 60 km from Vienna (in Austria) and 220 km from Budapest. The people of this city are famous for their loyalty to their country, and their hometown. A famous monument is 'Gate of Faith' which is the symbol of the people's faith to Hungary in 1921.
At the time of the Roman Empire, there was a city here called Scarbantia. The main square of Sopron is in the same place as the forum (or main square) of Roman times.
After this, the city was probably deserted. When the Hungarians arrived in the area, it was in ruins. In the 9th–11th centuries Hungarians strengthened the old Roman city walls and built a castle. The town got its Hungarian name of Sopron from a steward of the castle named Suprun. By 1153 it was an important town.
In 1273 King Otakar II of Bohemia took over the castle and took the children of Sopron's noble families as hostage. But the people of the city opened the gates when the army of King Ladislaus IV of Hungary arrived. The King Ladislaus made Sopron a free royal town.
In 1528 Hungary was invaded by Ottoman Turks who destroyed many parts of the city but did not take it over. Many people from other towns fled to Sopron for safety.
In 1676 most of the ancient buildings in the city were destroyed by a fire. When they were replaced, they were in a new style, called Baroque. Many of the Baroque buildings are standing today.