Color blindness is caused, in most cases, by inherited genetic changes that affect the light-sensing cells in your eyes. About 8% of males and 0.4% of females are born with some form of color vision deficiency. Less commonly, color blindness can develop later in life from eye diseases, certain medications, chemical exposures, or simply aging.
How Your Eyes See Color
Your retina contains three types of cone cells, each sensitive to a different range of light wavelengths: short (blue), medium (green), and long (red). No single cone can actually detect color on its own. Each one simply counts how many photons it absorbs, regardless of wavelength. Your brain figures out color by comparing the signals from all three cone types against each other. When one type of cone is missing, damaged, or slightly “off-tune,” that comparison breaks down and certain colors become difficult or impossible to distinguish.
Color vision deficiency falls into two broad categories. In dichromacy, one cone type is completely nonfunctional, so you perceive color using only two channels. In anomalous trichromacy, all three cone types work, but one responds to a slightly shifted range of wavelengths than normal, creating more overlap between cone signals and making fine color distinctions harder. Anomalous trichromacy is far more common and generally milder.
The Genetic Cause Behind Red-Green Deficiency
The genes responsible for red-sensitive and green-sensitive cone pigments sit on the X chromosome. Because this trait follows an X-linked recessive inheritance pattern, it hits men and women very differently. Males have only one X chromosome, so a single altered gene is enough to cause the condition. Females have two X chromosomes, meaning both copies would need to carry the change for color blindness to appear. A woman with one affected copy is a carrier: she sees color normally but can pass the trait to her children.
One important detail of X-linked inheritance is that fathers cannot pass the trait to their sons. A colorblind father passes his X chromosome only to his daughters, who become carriers. Those carrier daughters then have a 50% chance of passing the affected gene to each of their sons. This is why color blindness often seems to skip a generation, appearing in a grandfather and then his grandson through his daughter.
The specific genetic change usually involves either a missing gene or a hybrid gene that fuses portions of the red and green pigment instructions. When the gene is missing entirely, the result is dichromacy. When a hybrid gene produces a pigment whose sensitivity falls somewhere between normal red and green, the result is anomalous trichromacy, a milder form where colors look slightly “off” rather than indistinguishable.
Types of Inherited Color Blindness
Deuteranomaly, a reduced sensitivity to green light, is the most common form of color blindness overall. People with this condition have three working cone types, but the green-sensitive cones respond to wavelengths slightly closer to red than they should. Colors still appear, but greens and reds can look more similar than they do to someone with typical vision.
Protanomaly is similar but involves the red-sensitive cones being shifted toward green wavelengths. People with protanomaly need more red light than usual to match colors that most people see easily. Both protanomaly and deuteranomaly are red-green deficiencies, which is why they’re often grouped together, but the experience of each is subtly different.
The more severe versions, protanopia and deuteranopia, involve a complete absence of red or green cone function. Someone with protanopia sees no red light at all and matches colors using only green and blue. Someone with deuteranopia perceives no green light and relies on red and blue. These are less common than the anomalous forms but more visually limiting.
Tritanomaly and tritanopia affect the blue-sensitive cones and are extremely rare. Unlike red-green deficiencies, blue cone conditions are not X-linked. They follow a different inheritance pattern and affect men and women at similar rates.
Why Men Are Affected Far More Often
The 20-to-1 ratio between affected males and females comes directly from X-linked genetics. With roughly 8% of men carrying one altered gene on their single X chromosome, the condition is common. For a woman to be colorblind, she would need to inherit the altered gene from both parents, which requires a colorblind father and a carrier (or colorblind) mother. That combination is statistically uncommon, which is why prevalence in women hovers around 0.4% to 0.8% depending on the population studied.
Prevalence also varies across ethnic groups. Studies of different populations have found combined rates ranging from about 2.5% to over 7%, with some of this variation likely reflecting how frequently the altered genes appear in a given gene pool.
Diseases That Cause Color Vision Loss
Not all color blindness is genetic. Damage to the retina, optic nerve, or the visual processing areas of the brain can produce acquired color vision deficiency at any age. Common culprits include glaucoma, age-related macular degeneration, and diabetic eye disease, all of which damage the retina over time. Neurological conditions like multiple sclerosis and Alzheimer’s disease can also impair color perception by affecting the optic nerve or brain.
Unlike inherited color blindness, which is stable throughout life, acquired forms can worsen over time as the underlying disease progresses. They can also affect one eye more than the other, which is a key difference. Inherited color blindness is always symmetrical.
Medications and Chemical Exposures
Several widely used medications can interfere with color vision. Hydroxychloroquine, commonly prescribed for rheumatoid arthritis and lupus, can cause retinal toxicity that reduces both sharpness and color discrimination. Ethambutol, a tuberculosis drug, can damage the optic nerve in a dose-dependent way, with toxicity rates climbing from under 1% at lower doses to 18% at higher doses. Tamoxifen, used in breast cancer treatment, can cause crystalline deposits in the retina that affect color and visual clarity. Even digoxin, a heart medication, is known for causing a characteristic yellowish tint to vision.
Some of these effects are reversible when the drug is stopped. Others, particularly with prolonged use, can cause permanent damage.
Occupational chemical exposures pose a separate risk. Workers regularly exposed to organic solvents like benzene, toluene, and xylene show measurable color vision impairment even at exposure levels considered within safety limits. Gas station attendants, painters, and industrial workers face the highest risk. The damage appears to be neurotoxic, affecting the visual pathway rather than the cones themselves.
How Aging Changes Color Perception
Color discrimination naturally declines with age, even in people with no eye disease. The lens of the eye gradually yellows over decades, filtering out more short-wavelength (blue) light before it reaches the retina. Cataracts accelerate this process significantly, creating a brownish filter that makes blues look duller and shifts overall color perception toward warmer tones.
Interestingly, research suggests lens yellowing alone doesn’t fully explain the decline. When scientists simulated the yellow tint of an older lens in younger people’s eyes, it had little effect on their color discrimination scores. Other age-related factors, including changes in pupil size, retinal pigment, and neural processing, likely contribute as well. This means the aging of color vision is a whole-system decline, not just a lens problem.
How Color Blindness Is Detected
The most familiar screening tool is the Ishihara test, a set of dotted plates with numbers hidden in colored circles. It’s effective for catching red-green deficiencies but has notable limitations. It can’t distinguish between protan and deutan types, and it performs poorly at detecting acquired color vision loss from diseases like optic nerve inflammation, where its sensitivity drops to about 48%.
More comprehensive plate-based tests can identify the specific type and severity of deficiency. In clinical comparisons, these newer tests detected acquired color vision problems with 79% sensitivity while maintaining perfect specificity, making them significantly more accurate for people whose color vision has changed due to medical conditions rather than genetics. If you suspect your color vision has shifted later in life, mentioning it to an eye care provider can prompt the right type of testing.