Color blindness is a condition in which a person has difficulty seeing red, green, blue or a combination of these colors. In rare cases, a person may see no color at all. Color blindness is more common in males than females and is typically genetic (inherited or passed on from parent to child). Genetic color blindness is caused by a mutation of the X chromosome. Since only males have an X chromosome, 8% of men are affected, while only 0.5% of women.
Scientifically speaking, cone cells in the eye (there are approximately 6 to 7 million) control color sensitivity. Different cones – red, green and blue – perceive colors. These cells are concentrated in the center of the retina in an area called the macula. If a person is missing one of these cone cells, or one of the cone-types is malfunctioning, then color perception becomes irregular. This could mean a color is not at all visible or that colors appear in different shades.
Though the majority of those with colorblindness were born with it, it can be developed after an injury, as an effect of aging or medication, or as a consequence of other eye diseases.
Color vision problems often make reading, and sometimes even learning in general, more challenging. It can even limit career choices to positions that do not require the ability to discern colors.
Color Blindness Tests
There are two common types of tests performed to diagnose and assess color blindness.
- The Ishihara Color Test (also known as the Ishihara Plates Test) was created in 1917 by Dr. Shinobu Ishihara. It remains the most commonly used test today and consists of 38 plates. The plates contain sets of colored dots with an inlaid pattern – a letter or number. When a patient with a color vision problem is tested, the issue typically appears within the first few plates. The standard administration of the test (all 38 plates) will assess the severity of the color blindness.
- The Farnsworth D-15 arrangement test was created in 1947 by U.S. Navy Commander Dean Farnsworth and requires the arrangement of colored chips or blocks ordered according to the similarity of their hues. The test determines the type of color blindness as well as the severity of the condition.
Types of Color Blindness
After the testing and assessment, color blindness is classified into three common types. The mildest and most common is known as green deficiency while the second most common is red deficiency. These color deficiencies make up nearly all the cases of color blindness.
Color Blindness is classified as follows from most common to least common:
- Red-green Color Deficiency.
- Blue-yellow Color Deficiency.
- Total Color Deficiency (True Color Blindness).
People who are truly color blind see the world in black, gray and white. Other conditions commonly referred to as colorblindness are, in reality, color vision problems or color deficiencies. These are more critical than common colorblindness.