What Is Red-Green Color Blindness?

Red-green color blindness is the most common type of color blindness, a condition in which a person has limited ability to differentiate between certain colors. In red-green color blindness, this means difficulty distinguishing between shades of red, green, and yellow. Sharpness of vision typically is not affect. Color blindness is almost always inherited, in which case it cannot be treated, although there are ways for coping with it.

How the Eyes Perceive Color

The eye perceives color with a specific type of photoreceptor cell in the retina called a cone. (Photoreceptors are the cells that detect light; rods are the other type of photoreceptor cell.) Cones are concentrated in the center of the retina; besides perceiving color these cells make it possible to see fine details.

The retina has approximately 6 million cones. Each type of cone is sensitive to different wavelengths of visible light. There are three types of cone cells, each making up a certain percentage of the total cones in the retina:

• Red-sensing cones (60%)
• Green-sensing cones (30%)
• Blue-sensing cones (10%)

Color blindness can occur when one or more of the cone types do not function properly.

Symptoms of Red-Green Color Blindness

The primary symptom of red-green color blindness is a diminished ability to see differences in red, green, and yellow. Most cases are mild; in fact, some people never realize they aren't perceiving these colors as sharply as they could.

However, parents may notice early signs of color blindness in children:

• Using the wrong colors for an object–for instance, coloring leaves on trees purple
• Using dark colors inappropriately
• Seeming lack of interest when coloring in worksheets
• Difficulty identifying colored pencils with red or green in their composition (for example, purple and brown)
• Diminished ability to identify colors in low level light or in small areas
• Inability to distinguish easily between colors of the same hue
• Smelling food before eating
• Enhanced sense of smell
• Exceptional night vision
• Sensitivity to bright lights
• Problems reading pages or worksheets produced with color on color
• Complaints of eye or head pain when looking at a red image on a green background or vice versa.

Causes

Color blindness is caused by a reduced number of cone cells in the retina of the eye. In varying forms of color blindness, there can be a reduced number of cone cells, a reduction of cone density, or the number of cone cells within the macula, and defective or malfunctioning cone cells in the retina. 

The most common form of color blindness is inherited. Women can be carriers of hereditary forms of color deficiency that is passed through a defect in the X chromosome. However, because women have 2 copies of the X chromosome, women are not affected as frequently as men because their "normal" X chromosome compensates for the abnormal one. Female carriers of the abnormal gene can, however, pass on the defective X chromosome to their children, including their sons who will then manifest the condition. White men are disproportionately affected.

However, color blindness can be acquired, typically as a complication of diseases and conditions that affect the retina or the optic nerve, including:

• Eye diseases such as macular degeneration and glaucoma
• Brain and nervous system diseases, such as Alzheimer’s or multiple sclerosis
• Side effects of drugs such as Plaquenil (hydroxychloroquine) used to treat rheumatoid arthritis
• Aging
• Eye or brain injuries
• Leukemia
• Sickle cell anemia
• Chronic alcoholism

Diagnosis

The American Academy of Ophthalmology does not recommend routine testing for color blindness as part of routine comprehensive eye exams. However, the conditions is easy to diagnose using a simple test called the Ishihara test.

This test involves looking at images formed by multicolored dots on a field of multicolored dots of a different color, known as a pseudoisochromatic plate. People who are color-blind will be unable to distinguish between the different colors in order to identify the image.

Coping

There is no cure for inherited color blindness, but there are ways to cope with it if it is severe enough to interfere with everyday tasks. For example, if you drive it's important to memorize the order of traffic lights. Other options:

• Glasses and contacts: Special contact lenses and red-green color blindness glasses may help you tell the difference between colors.
• Visual aids: You can use visual aids, apps, and other technology to help you manage color blindness.
• Labeling items by color: This can be especially helpful for identifying personal items such as toothbrushes and face towels and coordinating outfits.

Color blindness caused by a health problem may subside once the underlying condition is treated. For instance, if you’re taking a drug that causes color blindness, your healthcare provider may adjust your dosage or suggest switching to a different prescription.

EnChroma Glasses

EnChroma glasses feature tinted plastic lenses coated with nearly 100 layers of dielectric material that filters out specific wavelengths of light that overlap in red-green color blindness. Although EnChroma glasses do not improve color contrast enough that a person can pass a color blindness test, it does help people with color blindness get a taste of what it is like to have color vision.

EnChroma glasses aren't a cure-all, nor will they appreciatively improve a person's ability to distinguish color. At best they help people with color blindness better appreciate things like an orange blazer or a lavender flower petal. They also take about 30 minutes to take effect and are expensive.

A Word From Verywell

If you have color blindness, you've likely figured out ways to prevent it from interfering with your daily life. If you have a child you suspect may be color-blind, however, take them to a pediatric ophthalmologist for confirmation. The sooner you know the extent to which your child's ability to distinguish between colors is impaired, the better able you'll be to help them learn to deal with it.