how is colour blindness caused ? how it can be cured?
What is color blindness?
Color blindness means that you have trouble seeing red, green, or blue or a mix of these colors. It’s rare that a person sees no color at all.
Color blindness is also called a color vision problem
What causes color blindness?
Most color vision problems are inherited (genetic) and are present at birth.
People usually have three types of cone cells in the eye. Each type senses either red, green, or blue light. You see color when your cone cells sense different amounts of these three basic colors. Most cone cells are found in the macula, which is the central part of the retina.
See a picture of the eye 
that shows the retina and the macula.
Inherited color blindness happens when you don't have one of these types of cone cells or they don't work right. You may not see one of these three basic colors, or you may see a different shade of that color or a different color. This type of color vision problem doesn't change over time.
A color vision problem isn't always inherited. In some cases, a person can have an acquired color vision problem. This can be caused by:
- Aging.
- Eye problems, such as glaucoma, macular degeneration, cataracts, or diabetic retinopathy.
- Injury to the eye.
- Side effects of some medicines.
What are the symptoms?
The symptoms of color vision problems vary:
- You may be able to see some colors but not others. For instance, you may not be able to tell the difference between red and green but can see blue and yellow.
- You may see many colors, so you may not know that you see color differently from others.
- You may only be able to see a few shades of color, while most people can see thousands of colors.
- In rare cases, you may see only black, white, and gray.
How is color blindness diagnosed?
Tests measure how well you recognize different colors.
- In one type of test, you look at sets of colored dots and try to find a pattern in them, such as a letter or number. The patterns you see help your doctor know which colors you have trouble with.
- In another type of test, you arrange colored chips in order according to how similar the colors are. People with color vision problems cannot arrange the colored chips correctly.
Because a color vision problem can have a big impact on a person's life, it is important to detect the problem as early as possible. In children, color vision problems can affect learning abilities and reading development. And color vision problems may limit career choices that require you to tell colors apart. Most experts recommend eye exams for children between ages 3 and 5. Vision screening is recommended for all children at least once before entering school, preferably between the ages of 3 and 4.