Colour Blindness

Colour blindness, more accurately called color vision deficiency, is a condition where you see colors differently than most people. While many think it means seeing no color at all, most people with this condition simply have trouble distinguishing between certain colors, especially reds and greens.

color vision deficiency, color anomaly, color deficiency, impaired color vision

Table of contents

• What is colour blindness?
• Types of color vision deficiency
• Symptoms
• Who is at risk?
• What causes colour blindness?
• Diagnosis
• Treatment and management
• Living with colour blindness
• Future treatments

What is colour blindness?

If you have colour blindness, it means you see colors differently than most people. Most of the time, color vision deficiency makes it hard to tell the difference between certain colors^[1]. The term “color blindness” can be misleading because true color blindness, where everything is seen in shades of black and white, is actually very rare^[2].

• Retina
• Cone cells
• Optic nerve
• Visual cortex

Your vision depends on special nerve cells in your retinas called photoreceptors, which turn light into nerve signals your brain uses to create your vision^[5]. One type of photoreceptor, called cones, helps you see and tell colors apart. There are three types of cones that each sense a different color of light: red-sensing cones (L cones), green-sensing cones (M cones), and blue-sensing cones (S cones)^[5].

Usually, your eyes use all three cones to sense and put together information that tells your brain what color something is. They use each of these colors together to make every other possible color. Color vision deficiency happens when you’re born without enough cones, or they don’t work like they should^[5].

Types of color vision deficiency

The most common type of color vision deficiency makes it hard to tell the difference between red and green. Another type makes blue and yellow look the same. In rare cases, people have complete color vision deficiency, which means they don’t see color at all^[1].

Red-green color deficiency

Red-green color blindness is the most common type. If you have it, you’ll have trouble seeing colors or shades that have red or green^[5]. About 99% of people with red-green color blindness have trouble with green perception (75%) or red perception (24%)^[6]. This type includes several subtypes:

Protanomaly means you have all three cones, but your red-sensing cones don’t work as well as they should. Red may appear as dark gray, and every color that contains red may be less bright^[5].

Deuteranomaly is the most common subtype of color blindness. You have all three cones, but your green-sensing cones don’t work correctly. You’ll see mostly blues and yellows, and most colors will look muted or softer than they should^[5].

Protanopia means you’re missing red-sensing cones. You won’t be able to see red. Most colors will look like a shade of blue or gold. You’ll probably have a hard time telling the difference between red and black^[5].

Deuteranopia means you don’t have green-sensing cones. You’ll mostly see blue and gold. It might be hard to tell the difference between red and green, or between green and yellow^[5].

Blue-yellow color deficiency

Blue-yellow color blindness happens when your blue cones are missing or don’t work correctly. It’s rarer than red-green^[5]. This type includes:

Tritanopia means your retinas are missing blue cones. You won’t be able to see any blue. You’ll mostly see red, pink and lavender^[5].

Tritanomaly means you have all the cones, but the blue-sensing ones don’t work completely. Blues will look green, and you probably won’t be able to see yellows well^[5].

Complete color blindness

Achromatopsia is the most severe form of color blindness and prohibits the individual from seeing any color. This condition may be associated with other eye conditions such as amblyopia (lazy eye), nystagmus (small, jerky eye movements), extreme light sensitivity, and severely poor vision^[6].

Symptoms

The main symptom of color vision deficiency is not seeing colors the way most people do^[1]. If you have color vision deficiency, you may have trouble seeing the difference between colors, how bright colors are, or different shades of colors^[1].

Symptoms of color vision deficiency are often so mild that they’re hard to notice. That’s why many people with color vision deficiency don’t know they have it. And people usually adjust to differences in how they see color^[1].

Some people figure out that they or their child has the condition when it causes confusion, such as when there are problems differentiating the colors in a traffic light or interpreting color-coded learning materials^[2].

People with very serious cases of color vision deficiency might have other symptoms, too, like quick side-to-side eye movements (nystagmus) or sensitivity to light^[1].

Who is at risk?

Men have a much higher risk than women for color vision deficiency^[1]. About one in 12 men (8%), but also about one in 200 women (0.5%) have red-green color blindness^[4]. Red-green color blindness is more common in males because the condition affects mainly men due to the genes responsible being located on the X chromosome^[3].

You’re also more likely to have color vision deficiency if you have a family history of color vision deficiency, have certain eye diseases, have certain health problems like diabetes, Alzheimer’s disease, or multiple sclerosis, take certain medicines, or are white^[1].

Testing children

Color blindness is usually detected in children during their early school years. It is not until children are learning the names of colors that color blindness is noticed^[16]. It can be tricky to diagnose color vision deficiency in children. Kids who have color vision deficiency may try to hide it. But having color vision deficiency can make it hard to read from a chalkboard or do other activities^[1].

Get your child’s eyes tested if they have a family history of color vision deficiency or if they seem to be having trouble learning colors^[1]. Early signs of color blindness in school include using the wrong colors when drawing an object, smelling food before eating it, or trouble reading with colored pages^[6].

What causes colour blindness?

Most people who have color vision deficiency are born with it. This is because the most common types of color vision deficiency are genetic, meaning they’re passed down from parents^[1].

The most common types of color blindness are the red-green types, which are caused by recessive genes on the X chromosome. These genes cause a molecular substitution to be expressed in the retinal photopigment molecule, which in turn causes its spectral absorption to be shifted in such a way that the available information is reduced^[4].

Because of the X-linked recessive biology behind red-green color blindness, if a mother has color blindness, the chances that her son also has color blindness is very high because the female passes the disorder on her X chromosome^[16].

Color vision deficiency can also happen because of an injury to the retina (the light-sensitive layer of tissue in the back of the eye), the optic nerve (which connects the eye to the brain), or the brain itself^[1]. Some examples of injuries that can lead to color vision deficiency are retinal detachment (when the retina is pulled away from its normal position at the back of the eye), eye injuries caused by lasers, some kinds of brain tumors especially ones that affect the optic nerve or put pressure on the brain, and radiation treatments^[1].

Besides being born with color blindness, it can also be caused by other conditions like Alzheimer’s and other chronic diseases^[16]. Diabetes can cause color blindness because diabetes can cause damage to the back of the eye, where the cones in the eye are located^[16]. Color vision also naturally degrades in old age^[3].

There are some types of color blindness that are not genetic and can develop after birth. The most common type of these is caused by a drug used to treat rheumatoid arthritis called Plaquenil^[6].

Diagnosis

If you have trouble seeing certain colors, an eye care professional can test for a color deficiency. Testing likely involves a thorough eye exam and looking at specially designed pictures^[7].

Color blindness is usually diagnosed by an optometrist by using a series of simple screening tests. These pictures are made of colored dots that have numbers or shapes in a different color hidden in them. If someone has a color vision deficiency, they’ll find it difficult or impossible to see some of the patterns in the dots^[7].

Tools such as the Ishihara test and Hardy-Rand-Rittler tests are used to determine the severity of the color deficiency. During these tests, the patient identifies numbers and letters in images made up of colored dots. The optometrist then uses this information to diagnose a color deficiency^[17].

Treatment and management

Usually, color vision deficiency runs in families. There’s no cure, but special glasses and contact lenses can help people see differences between colors. Most people who have color vision deficiency don’t have problems with everyday activities^[1].

There are no treatments for most types of color vision difficulties, unless the color vision problem is related to the use of certain medicines or eye conditions. Stopping the medicine causing the vision problem or treating the underlying eye disease may result in better color vision^[7].

Special glasses and lenses

Wearing a colored filter over eyeglasses or a colored contact lens may enhance perception of contrast between the confused colors. But such lenses won’t improve the ability to see all colors^[7]. Specialized glasses can improve your color perception by filtering light in ways that help make colors stand out more clearly. These glasses won’t “cure” color blindness, but they can make daily tasks like choosing clothes or reading traffic lights more manageable^[15].

Practical strategies

There are several ways to help those with color blindness overcome obstacles in everyday life:

• Memorize the order of colored objects. If it’s important to know individual colors, such as with traffic lights, memorize the order of the colors^[7].
• Label colored items that you want to match with other items. Have someone with good color vision help you sort and label your clothing^[7].
• Use technology and apps. There are many apps designed to assist with color recognition. These apps can use your phone’s camera to identify colors and either read them aloud or show them on the screen^[15].
• Focus on patterns and textures to help identify things, rather than relying on color^[15].
• Use bright, natural lighting when possible, as yellow or dull lighting can make it even harder to perceive color^[13].

Living with colour blindness

Color blindness is a minor disability. However, there are some real challenges for people who are suffering from moderate to strong color vision deficiency^[19]. A sunburn can’t really be seen, only if the skin is almost glowing. If meat is cooked can’t be told by its color. Flowers and fruits can’t be easily spotted sometimes, and you can’t tell if a fruit or vegetable is ripe or not yet^[19].

Every electrical device which uses LED lights to indicate something is a permanent source of annoyance. Colored maps and graphics can sometimes be very hard to decipher. By far the biggest issue is matching colors, and specially matching clothes^[19].

When cooking, instead of determining if a steak or piece of chicken has been cooked thoroughly based on the center of the meat’s color, use a meat thermometer. This is the safest way to tell if your food is safe to eat regardless of a vision deficiency^[13].

Don’t be afraid to let people know about your color blindness if you feel comfortable doing so. Being open allows others to help, especially when color identification is important^[15]. Many people with color blindness borrow the eyes of family members and friends to help them with tasks like matching clothing or choosing colors^[19].

Impact on careers

Professions that require good to perfect color vision include airline pilot, air traffic controller, firefighter, police officer, train driver, some ranks in the armed forces, and some electrical/electronic engineers^[19]. Jobs which require good color vision can be split into two different categories. In the first, color matching or color recognition is a main component of the job. This includes color quality control, art teaching, interior decorating and more^[19].

In some countries, color blindness can limit career choices. In Japan, individuals with this condition are not allowed to perform certain jobs and sometimes are not even allowed to drive a car. In the United Kingdom, color blindness is not considered a disability^[6].

Future treatments

People who are color blind may one day have an opportunity to experience the full spectrum of color vision. Researchers at the University of Washington have developed gene therapy that restores the gene that codes for the missing or faulty light-sensitive pigment, allowing cone cells to detect colors that they could not detect previously^[10].

The therapy has been tested in animals that have cone cells sensitive to wavelengths of blue and green light but insensitive to those for red light. A few months after therapy, treated animals could distinguish an image formed from red dots embedded within a field of dots of varying colors, while untreated animals remained blind to the embedded image^[10].

Jay and Maureen Neitz of the University of Washington have teamed with a California biotech firm to develop what they say may be a solution: a single shot in the eye that reveals the world in full color. Together, they’ve found a new way to deliver genes that can replace missing color-producing proteins in certain cells, called cones, in the eyes^[11].

While the research into gene therapy for red-green colorblindness has lagged, successful human trials are ongoing for achromatopsia^[12]. Testing of a gene therapy for achromatopsia is slated to begin, and gene therapy is starting to work and is changing this field^[10].