Color blindness, or color vision deficiency, affects millions of people worldwide, making it challenging to distinguish between certain colors. While most people with this condition are born with it due to genetic factors, understanding how it works and learning to adapt can help those affected live full, independent lives.

Epidemiology

Color blindness is a surprisingly common vision condition that affects a significant portion of the global population. Estimates suggest there are approximately 350 million people worldwide living with red-green color blindness, which represents about 4 percent of the total population^[4]. The condition shows a striking difference between males and females in terms of how frequently it occurs.

Men are much more likely to experience color vision deficiency than women. About one in twelve men, or roughly 8 percent, have some degree of red-green color blindness, while only about one in 200 women, or 0.5 percent, are affected by this condition^[3][4]. This dramatic difference relates to how the condition is passed down through families, which we’ll explore further in the causes section.

The prevalence also varies across different ethnic groups. Research has found that color blindness is most common in non-Hispanic white boys, affecting about 5.6 percent of this population. It appears less frequently in Black boys at 1.4 percent, with Asian children at 3.1 percent and Hispanic children at 2.6 percent falling somewhere in between^[16]. White individuals overall appear to have a higher risk of developing color vision deficiency^[1].

While red-green color blindness receives the most attention due to its prevalence, blue-yellow color deficiency may also be quite common, though precise statistics are harder to establish. Some estimates suggest the total number of people affected by blue-yellow color blindness may be at least as high as those with red-green deficiency, and these numbers may be increasing due to aging populations worldwide^[4].

Causes

Understanding what causes color blindness requires looking at how our eyes work. The light-sensitive layer at the back of the eye, called the retina, contains special nerve cells called photoreceptors that turn light into electrical signals your brain can interpret. Among these photoreceptors are cells called cones, which are specifically responsible for color vision^[5].

Most people have three types of cones, each sensitive to different wavelengths of light. Red-sensing cones (also called L cones) respond to longer wavelengths around 560 nanometers, green-sensing cones (M cones) absorb light near 530 nanometers, and blue-sensing cones (S cones) absorb shorter wavelengths near 420 nanometers^[12]. Your brain compares signals from these three cone types to create the full spectrum of colors you perceive.

The overwhelming majority of people with color blindness are born with the condition. This happens because the most common types of color vision deficiency are genetic, meaning they’re inherited from parents^[1]. The genes responsible for producing the light-sensitive proteins (called opsins) in the cones can be missing or faulty. When one or more of these genes doesn’t work properly, the affected cones either don’t function correctly or are absent entirely, leading to altered color perception^[4][5].

These genetic mutations cause what’s known as a molecular substitution in the retinal photopigment molecule, which shifts how it absorbs light. This shift reduces the available color information, as the absorption ranges of different cone types overlap more than they should^[4].

A drug used to treat rheumatoid arthritis called Plaquenil is noted as one of the most common medications that can cause acquired color blindness^[6]. Additionally, color vision naturally tends to decline with age, even in people who had normal color vision throughout their younger years^[3][4].

Risk Factors

Several factors can increase a person’s likelihood of having color vision deficiency. The most significant risk factor is biological sex. Men have a much higher risk than women for color blindness because of how the genetic condition is passed down through families^[1][8].

This sex-linked pattern occurs because the genes responsible for the red and green cone pigments are located on the X chromosome. Males have one X and one Y chromosome, while females have two X chromosomes. For a male, just one faulty X chromosome is enough to cause color blindness. However, females would need both of their X chromosomes to carry the defective gene to be affected, which is much less likely^[3][16]. If a mother has color blindness, the chances that her son will also be color blind are very high because she will pass the affected X chromosome to him^[16].

Family history is another major risk factor. If you have relatives with color vision deficiency, particularly on your mother’s side of the family, you’re more likely to have it yourself^[1][8]. This is why eye doctors often ask about family history when screening for the condition.

Certain health conditions increase your risk of developing color blindness later in life. People with diabetes are at higher risk because elevated blood sugar can damage the back of the eye where the cones are located^[17]. Other conditions that raise risk include Alzheimer’s disease, multiple sclerosis, and various eye diseases such as glaucoma and macular degeneration^[1][8][17].

Taking certain medications, being white, and advancing age are also factors that can increase the likelihood of experiencing color vision problems^[1][8]. Exposure to harmful chemicals or medical treatments can also contribute to developing acquired color blindness^[2].

Symptoms

The main symptom of color vision deficiency is seeing colors differently than most people do. However, this doesn’t mean that people with color blindness see no color at all, despite what the name suggests. Instead, they have difficulty distinguishing between certain colors or seeing different shades of the same color^[1][2].

For people with the most common type of color blindness, red-green color deficiency, it becomes hard to tell the difference between various shades of red and green. They might confuse these colors with each other or with other colors entirely. For instance, someone might have difficulty distinguishing between red and black, green and brown, or pink and gray^[4][5].

Those with blue-yellow color blindness struggle with shades of blue and confusions between blue and green colors. They may also have trouble seeing yellows clearly^[4][5]. In these cases, colors like blue might appear green, and yellow may be difficult to perceive at all.

The symptoms of color vision deficiency are often quite mild, which means many people don’t even realize they have it. People naturally adjust to the way they see colors, assuming everyone sees the world the same way they do^[1][8]. It’s not uncommon for someone to go years or even decades without knowing they have a color vision deficiency.

In everyday situations, people with color blindness may have trouble determining if colors match, seeing how bright certain colors are, or distinguishing different shades of the same color^[1]. These difficulties can affect various daily activities in subtle but important ways.

People with very serious cases of color vision deficiency, particularly complete color blindness (where they see only in shades of gray), may experience additional symptoms beyond just altered color perception. These can include rapid, involuntary side-to-side eye movements called nystagmus, extreme sensitivity to light, and severely reduced vision overall^[1][6][8].

Prevention

For the inherited forms of color blindness, which account for the vast majority of cases, there is unfortunately no way to prevent the condition. Since these types are passed down genetically from parents to children through chromosomes, they are present from birth and cannot be avoided through lifestyle changes or medical interventions^[1][3].

However, because color vision deficiency can sometimes develop later in life due to other medical conditions or exposures, managing your overall health can help reduce the risk of acquired color blindness. Taking good care of your eyes and body is important.

Managing chronic health conditions properly, particularly diabetes, may help prevent damage to the eyes that could affect color vision. Since diabetes can harm the back of the eye where cone cells are located, keeping blood sugar levels well-controlled through proper diet, medication, and regular medical care is beneficial^[17].

Regular eye examinations are valuable for detecting any changes in vision early, including problems with color perception. If you have a family history of color vision deficiency or other eye diseases, letting your eye doctor know can help them monitor for potential issues.

Being aware of medications you take is also wise. If you’re prescribed medications that have been associated with color vision changes, such as certain drugs used for rheumatoid arthritis, discussing potential side effects with your doctor and having your vision monitored can be helpful^[6].

For children with a family history of color blindness, early testing is important not for prevention, but for early identification. Getting your child’s eyes tested if they have a family history of the condition or if they seem to struggle learning colors allows for earlier support and adaptation strategies^[1][8]. This testing can occur through their eye doctor or sometimes through school screening programs.

Pathophysiology

To understand how color vision deficiency affects the body, we need to look at the normal process of color vision and what changes when someone has color blindness. Your eyes work like sophisticated cameras that capture light from the world around you and translate it into signals your brain can understand.

Light enters your eye through the front and travels to the retina at the back. The retina contains millions of photoreceptor cells that respond to light. There are two main types: rods and cones. Rods help you see in dim light and detect movement, but they don’t process color. Cones are responsible for color vision and work best in brighter light^[5][9].

In typical color vision, also called trichromatic vision, you have three types of cone cells. Each contains a different light-sensitive protein (opsin) that responds to a specific range of light wavelengths. Even though we think of them as red, green, and blue cones, they actually respond to long (L), medium (M), and short (S) wavelengths of light respectively^[5][12].

When light hits these cones, it triggers a chemical change in the opsin proteins. This chemical change gets converted into electrical signals that travel along the optic nerve to your brain. Your brain then compares the signals from all three types of cones. By analyzing the differences in how strongly each cone type responds, your brain can determine what color you’re looking at. These signals are processed through what scientists call “opponent channels” that perceive balances between red-green, blue-yellow, and black-white^[12].

In people with color vision deficiency, this system doesn’t work as intended. The problem typically lies with the cone cells themselves or the opsin proteins they contain. In the most common forms of red-green color blindness, either the red or green opsins are missing entirely, or they contain genetic mutations that cause them to function abnormally^[4][5].

When opsin genes are mutated, the proteins they produce may be shifted in how they absorb light wavelengths. This causes the absorption ranges of different cone types to overlap more than they should. When this overlap increases, the available color information decreases because the signals from different cone types become too similar for the brain to distinguish properly^[4].

People who are completely missing one type of cone are called dichromats because they only have two functioning cone types instead of three^[10]. This means one of their opponent process channels is inactive. For example, if someone lacks functional red or green cones, their red-green opponent channel doesn’t work, so they can’t distinguish between reds and greens. Their brain simply doesn’t receive the comparative information it needs to tell these colors apart.

Those who have all three cone types but with one that functions abnormally are called anomalous trichromats. They technically have three-color vision, but their color perception is shifted or reduced compared to typical vision^[10][12]. Colors may appear muted or different shades than what others see.

In very rare cases of complete color blindness (achromatopsia), either all cone types are missing or other parts of the cone cells’ machinery that transmit light signals to downstream neurons are broken^[12]. People with this condition rely solely on their rods for vision, which means they see only in shades of gray and experience poor visual acuity and severe light sensitivity.

For acquired color blindness that develops later in life, the pathophysiology involves damage to the existing color vision system. This could be physical damage to the retina from detachment or injury, damage to the optic nerve from tumors or pressure, degeneration of cone cells from diseases like glaucoma, or interference with the visual processing areas of the brain^[1][8]. In these cases, cone cells or the pathways that carry their signals may be working properly, but the system has been disrupted at some point along the way from eye to brain.