Color blindness is the condition in which a person can’t discern between certain colors. Ninety nine percent of individuals with color blindness cannot distinguish reds from greens. A more rare form of color blindness is the inability to see blues and yellows. Monochromasy, the ability to see only shades of grey is an extremely rare occurrence.

How Normal Eyes Perceive Color

Your eyes are comprised of many different parts, including the retina, which plays an important role in vision. Located at the back, inside of your eye, the retina is an area that includes cells called cones. The six to seven million cones that occupy the retina help your brain to perceive colors.

While more than 60 percent of your eyes’ cones are L-cones that read red wavelengths, over 30 percent are M-cones that read green wavelengths. The rest of the retina’s cones are known as S-cones, perceiving blue wavelengths.

What Causes Color Blindness?

Color blindness occurs when the retina’s cones do not work correctly or aren’t present in the eye. In general, people who suffer from color blindness inherit it as a defect on the X-chromosome. Because men only have one X-chromosome (and one Y-chromosome), any defects, including color blindness, that it carries will affect the resulting male child.

In contrast, women are the result of 2 X-chromosomes (and no Y-chromosome), meaning that any defect that one carries can be negated if the other X-chromosome is healthy. This means that a woman can only genetically inherit color blindness if both of the X-chromosomes carry the trait for color blindness. As a result, men are far more likely to inherit color blindness than women.

While color blindness is primarily an inherited defect, people may also suffer from this condition due to:

• brain damage
• damage to the retina or optical nerve
• retinitis pigmentosa
• side effects of Alzheimer’s disease, leukemia Parkinson's disease.

Types of Color Blindness

There are many types of color blindness, including:

• Anomalous Trichromacyis the condition in which the color-sensitive cones are damaged, preventing you from being able to identify certain colors. One type of anomalous trichromacy is protanomaly, in which L-cone damage causes trouble perceiving reds. Another type is deutanomoly, in which M-cone damage prevents normal perception of greens.

• Dicromasy is a type of color blindness that results from the complete lack of one type of cone. Dicromasy is a much more severe problem than anomalous trichromacy.
  
  The various types of dicromasy are based on the cone that you are missing. For example, if all your L-cones were missing, a condition known as protanopia, you would not be able to perceive colors in the red wavelengths. If you lacked M-cones, you would have deutanopia and would not be able to see greens wavelengths. If you didn’t have S-cones, you would not be able to see blue wavelengths and would have tritanopia.

• Monochromacy occurs when an individual is missing or has defective cones in two or three of the cone types. Those suffering from monochromacy can’t discern more than a few colors, if any at all. Monochromacy is the most severe type of color blindness.

Tests for Color Blindness

When it comes to diagnosing color blindness, doctors can use one or a combination of three existing diagnostic tests, including:

• Ishihara test: One of the most commonly used tests for color blindness is the Ishihara Color test, developed in 1917, that measures red and green deficiencies.
  
  The Ishihara tests consist of plates that use multiple colored dots of various sizes with a number "hidden" color spots within the dot pattern. When a person with normal vision looks at one of these dotted cards, he sees a circle filled with red dots, as well as dots of other colors that form a number in the middle of the circle.
  
  While those suffering from protanomaly (the inability to see red) will see a number different than the one that those with normal vision will see, those suffering from deutanomoly (the inability to see green) see yet another number. Thus, this test not only identifies the presence of color blindness but also the type of color blindness a person has.
  
  However, because the Ishihara test revolves around identifying numbers, it isn’t the best way to diagnose children. More commonly, color blindness tests for children call for kids to recognize shapes of different colors.

• American Optical/Hardy, Rand, and Ritter Pseudoisochromatic Test (A.O. / H.R.R.): This test is a watered down version of the Ishihara test. The A.O./H.R.R. test uses cards with colored dots to evaluate whether or not a person suffers from color blindness. Within a circle of dots of one color is a shape or number of another color of dots. While those with normal vision can see the inner shape, the color blind don’t. One of the biggest drawbacks to this test is that it doesn’t identify which type of color blindness a person has.

• Titmus II Vision Tester Color Perception Test: In this test, a stereoscopic machine presents a subject with six images set on a black background that is bordered by yellow. While this test is uniquely advantageous because it can test each eye individually, one of the main drawbacks to it is that it can only highlight the inability to see red and/or green. Similarly, because it isn’t always accurate, it is generally used in combination with another color blindness test.

Color Blindness Treatments

Unfortunately, there are currently no color blindness treatments for those who have inherited the disorder. However, because they have dealt with color blindness since birth, they adapt to this vision deficit early on in their lives.

If color blindness arises out of some other cause, then it may get better, may worsen or may stay the same over time.

If you suspect that you or your child are color blind, schedule an exam with your optometrist or ophthalmologist. Your doctor can teach you tools and techniques that can help you cope with this condition.