Color vision deficiency (color blindness)

People who have a color vision deficiency have difficulty seeing some colors, or they see them differently from other people. The condition is often inherited, and it affects more males than females. Around one or two in every 20 males will have some form of color vision problem.

The term “color vision deficiency” is more accurate than “color blind”. People who cannot see all colors can still see some colors, and they see other things, such as fine detail, just as clearly as people with full color vision. In the most common form, people cannot see the red and green components of colors, and may confuse red and green with each other or with yellow.

How the eye sees color#

All the cells and nerve pathways needed for vision are present from birth. In the retina, at the back of the eye, there are two types of light-sensitive cells: rod cells and cone cells.

• Rod cells are sensitive to low light. We use them to see at night, but only in shades of black, gray and white. There is just one type of rod cell.
• Cone cells react to brighter light and help us see detail. They also make color vision possible.

Usually there are three types of cone cell, which respond to long (red), medium (green) and short (blue) wavelengths of light. By comparing the signals from the three types of cone, the brain produces the wide range of colors that most people see. Someone with color vision deficiency lacks one or more types of cone cell, or has an altered response because of a genetic change or eye disease.

Signs in children#

Signs that a child may have a color vision difficulty include trouble recognizing and naming different colors, or being unable to sort objects by their color. Parents often first notice these signs when a child is learning to name colors.

What causes color vision deficiency#

Color vision deficiency is most commonly a genetic condition. It results from a change in one or more of the genes involved in producing the visual pigments (known as opsins) in the cone cells.

Red–green color vision deficiency is the most common inherited type. It occurs in about eight per cent of males and only about 0.4 per cent of females. This is because the genes involved sit on the X chromosome, so the condition is “sex-linked”. Males have only one X chromosome, while females have two. In females, a working gene on just one of the two X chromosomes is enough to produce normal color vision, so a changed copy can be compensated for. Males have no second copy to make up for a changed gene.

A change in another opsin gene causes blue-yellow color vision deficiency, which makes it hard to tell the difference between shades of blue and green. Yellow may also be hard to identify, sometimes appearing violet, gray or pink depending on the gene change involved. Blue-yellow color vision deficiency is very rare, affecting only about one in 10,000 people. Males and females are affected equally because this gene is on a non-sex chromosome.

Color vision deficiency is not always inherited. It can also develop later in life from other causes, including:

• degenerative eye disease, such as macular degeneration, glaucoma and retinitis pigmentosa
• other conditions such as diabetes, Alzheimer’s disease, leukemia, liver disease, chronic alcoholism, multiple sclerosis, Parkinson’s disease and sickle cell anemia
• trauma that damages the brain or retina
• exposure to certain toxins

Living with color vision deficiency#

Many everyday tasks rely on being able to tell things apart by their color. There are varying degrees of color vision deficiency, and the brightness of the light and the size of an object can also affect how well someone distinguishes colors.

When people cannot see a difference in color, they rely on other cues. For example, a person may tell red and green traffic lights apart by their position (red above green). On a dark, wet night this can be difficult. Most people who are color vision deficient can still tell apart the red and green lights used in modern traffic signals.

Driving#

People with red–green color vision deficiency are generally able to hold a car, motorcycle or commercial driver license. However, people with reduced contrast sensitivity may have restrictions placed on their license, such as not being permitted to drive at night. It is wise for drivers with a significant color vision deficiency to understand how it may affect their response to traffic lights and other road signals, and to adapt their driving accordingly.

Occupations#

People with a color vision deficiency may be restricted from certain occupations where reliable color recognition is essential. These can include some roles in policing, the armed forces, maritime work and other safety-related fields. If you are concerned about how it may affect your career, talk to prospective employers or recruiters, who can advise which roles are suitable for you.

Diagnosis#

If activities at school are color coded, children with color vision problems may struggle with those tasks. It is often recommended that all children, especially boys, have a routine color vision check in the early years of school.

Color vision testing can be done by ophthalmologists (eye specialists) and optometrists using specially designed charts, and some school health services can also test children’s color vision. If a deficiency is found, further testing may be needed to determine its exact nature.

Treatment and support#

There is generally no treatment that cures color vision deficiency. However, most people find they have few limitations, and some do not discover they have it until adulthood. Helpful adjustments include taking cues from others, using visual cues that do not rely on color, and using smartphone apps that assist with identifying colors.

If you or a family member has been diagnosed with color vision deficiency, or if it runs in your family, it can help to speak with a genetic counselor. Genetic counselors are health professionals qualified in both counseling and genetics. As well as providing emotional support, they can help you understand what causes the condition, how it is inherited, and what a diagnosis means for your or your child’s health and development.

Genetic counselors are trained to provide information and support that is sensitive to your family circumstances, culture and beliefs. If color vision deficiency runs in your family, a genetic counselor can explain the genetic testing options available to you and other family members. You may choose to see one if you are planning a family and want to understand your chance of passing the condition on to your child.

Key points#

• In the most common form of color vision deficiency, people cannot see the red and green components of colors
• Color vision deficiency is most commonly a genetic condition
• Red–green color vision deficiency is the most common inherited type
• A change in another opsin gene causes blue-yellow color vision deficiency
• For blue-yellow deficiency, males and females are affected equally because the gene is on a non-sex chromosome

Where to get help#