Colour blindness

Colour blindness is a fairly common condition where people have an altered perception of colour and may not appreciate as many shades or might get confused between different hues. Its official name is colour vision deficiency and is rarely full colour blindness (an absence of all colour vision). Colour blindness is usually genetic and happens when the cones (a type of nerve cell in your eyes’ retinas) aren’t working correctly or are missing. Cone cells process light and images as they enter your eye and are responsible for sending signals to your brain to allow you to perceive colour.

The majority of people with colour blindness do see some colours – but in a more limited spectrum – and may have more difficulty distinguishing certain colours or shades and perceiving brightness of colours.

Types of colour blindness

There are 3 main types of colour blindness that are commonly seen, and a third, very rare type of colour blindness which is an absence of all colour perception. The different types of colour blindness are defined according to which types of cones aren’t working well.

Cone cells in your eyes receive light signals from your environment and transmit those signals to your brain, which is then turned into perceived colour. The cones detect colours in the visible spectrum of light, which includes all the wavelengths that humans can see. These wavelengths range in length from 380 nanometers (short) to 700 nanometers (long). Three types of cones are responsible for detecting colours on these three wavelengths.

• Red-sensing cones (L cones) – These cones perceive long wavelengths (around 560-580 nanometers).
• Green-sensing cones (M cones) – These cones perceive middle wavelengths (around 530-540 nanometers).
• Blue-sensing cones (S cones) – These cones perceive short wavelengths (around 420-440 nanometers).

Most people have all three types of cones in their retinas and they all work correctly. But, if you have a colour vision deficiency, it means that one or more of these types of cones aren’t working properly, which can affect your ability to see colours in the traditional way.

The different ways in which your cones can affect your colour perception include:

• Trichromacy – All three types of cones are present and working correctly. You can accurately perceive and identify the full range of colours. This is also known as having full-colour vision.
• Anomalous trichromacy – You do have all three types of cones, but one type isn’t working quite right and isn’t as sensitive to light as it should be. Therefore, you don’t see colours in the traditional way. This type of colour blindness has names that end in “anomaly” (indicating partial vision of a specific colour).
• Dichromacy – This means you have one type of cone missing, leaving you with only two types of cones (usually S cones along with either L cones or M cones). These types of colour blindness have names that end in “anopia” (which means an absence of vision of a specific colour). Monochromacy – You only have one type of cone, or you have no cone function at all. You have very limited or no ability to see colour. Instead, you see the world in varying shades of grey and are often accompanied by poor vision.

Red-green colour vision deficiency

Red-green deficiency is the most common type of colour blindness. It affects the way you see shades of red and green. It’s more common in men and people assigned male at birth than women and people assigned female at birth.

There are 4 types of red-green colour vision:

• Protanopia – This means your L cones are missing so you can’t perceive red light. You mostly see colours as shades of blue or gold and might easily confuse different shades of red or brown with other colours like green, red, or orange.
• Deuteranopia – This type means that your M cones are missing which means you can’t perceive green light. You mostly see blues and golds and may confuse some shades of red with some shades of green. You may also confuse yellows with bright shades of green.
• Protanomaly – This means that you have all three cone types, but your L cones aren’t as sensitive to red light as they should be. Red might appear as dark grey, and every colour that contains red might appear muted.
• Deuteranomaly – You have all three cone types, but your M cones aren’t as sensitive to green light as they should be. You can see mostly blues, yellows, and most colours appear muted.

Blue-yellow colour vision deficiency

Blue-yellow colour blindness is much less common than red-green colour blindness is and most often occurs due to an ocular condition or disease.

It includes two different types:

• Tritanopia – This means you have no S cones so you can’t perceive blue light, the shortest wavelengths on the spectrum. You see the world in mostly reds, light blues, pinks and purples.
• Tritanomaly – This type means that you have all three types of cones, but your S cones don’t work as they should, making them less sensitive to blue light than they should be. Blues look more green, and you can see little to no yellow.

Complete colour vision deficiency

Complete colour vision deficiency is also known as monochromacy and means that you can’t see any colour at all. It’s very rare to not be able to see any colours, and you see the world in black and white.

Symptoms

The symptoms of colour blindness can be difficult to notice – how do you know something is wrong if you’ve grown up seeing the world this way? In fact, you might not notice there is a problem until you take a colour blindness test online. This is why it’s important for children to have a comprehensive eye exam before they start school.

The most common things people with colour blindness will have trouble seeing include:

• The different between colours
• How bright colours are
• Different shades of colours

Causes

Most people who have colour blindness are born with it, as the condition is usually caused by a recessive gene connected to the X chromosome and typically passed down from mother to son.

However, it can be caused by other factors such as:

• Trauma or damage to the optic nerve (the nerve that carries signals from your eye to your brain).
• Brain tumours that put pressure on the optic nerve.
• Radiation treatments.
• Some medications.

How common is colour blindness

It is a fairly common condition. Around 1 in 12 men and people assigned male at birth are colour-blind, while only 1 in 200 women and people assigned female at birth are colour-blind. 98% of colour-blind people have red-green colour vision deficiency.

Diagnosis

The Ishihara test is the most common type of colour blindness test that you may be familiar with. The test involves a series of plates that contain a pattern of coloured dots. Within these dots, there is a pattern (usually a number or shape for young children) to identify. Some plates include patterns that you can only see with full-colour vision, while others include patterns that can only be seen with a colour vision deficiency.

It’s important to note that although the Ishihara test is widely used with many optometrists, it is only a screening test and is only used as a way to gauge whether you need further colour blindness testing.

Treatment For those with genetic colour blindness, there is no cure, however most people adjust to life with colour blindness as they age. However, there are some jobs that you might find you are unable to do if you can’t tell the difference between colours such as graphic designer, electrician, train driver, armed forces, or pilot.

If your colour blindness is caused by another health condition, doctors will treat the condition that is causing the colour problem. Alternatively, if it is caused by a medication, your doctor may adjust the dose or suggest an alternative.

There are some tools available on the market to help with your colour blindness if you so choose:

• Glasses – touted to “correct” your colour blindness, these glasses are popular options with varied results. They may provide a richer colour experience by allowing the wearer to perceive more colour shades for people with mild forms of anomalous trichromacy but they don’t correct colour blindness like they promise. They also can’t be used in job suitability assessments.
• Visual aids – There are certain apps on that market that let people take photos with a phone or tablet and then tap on part of the photo to find out the colour.
• Many computers and phones now have settings to help people with colour vision deficiency.
• Invest in good quality lighting to help your colour vision at home.

If you or your child has colour blindness, it’s important to learn the type and severity. Speak to your optometrist to have your eyes tested and talk about the nature of your condition and how it might affect you.

Takeaway

Colour blindness is a fairly common condition that affects around 300 million people in the world. It’s a condition where the cones in your retinas that detect and signal the light spectrum to your brain aren’t working correctly or are missing. It is usually genetic and there is no cure, although in some cases, things like trauma to the optical nerve can also cause colour blindness which might be curable with treatment of the underlying cause.