Colour blindness is a condition where the light-sensitive cells in the retina fail to respond correctly to variations in wavelengths of light, causing a defect where people are unable to see colour properly.
But how do you know if your child is actually colour blind?
Dr Caroline Paulson, Specialist Ophthalmology, Zulekha Hospital Dubai, says that the majority of cases she encounters are diagnosed fairly early. “Commonly, when children are taught colours between the ages of two and three, parents identify that there are some particular colours that the child describes incorrectly and that is usually when they bring the child to an ophthalmologist.
It is predominantly a male problem as it is an X-linked recessive condition, so men tend to manifest colour blindness whereas women could be carriers but not manifest the symptoms.
“If the parent is very observant, they tend to recognise colour blindness in their children much earlier. Sometimes I see slightly older children. It is often undiagnosed because children with the most common type of colour blindness usually have otherwise ordinary vision.”
Dr Paulson says that the most common form of colour blindness is inherited and that it affects significantly more males than females. “It is predominantly a male problem as it is an X-linked recessive condition, so men tend to manifest colour blindness whereas women could be carriers but not manifest the symptoms. Predominantly it is a genetic condition.
“There are different types of colour blindness but the most common kind of colour blindness is red-green. Affected patients have an inability to differentiate between colours of red and green.
“There are less common subsets of colour blindness, where some patients cannot identify colour at all and they see everything in the world in shades of grey but that is very rare.”
Rods and cones
The cause of colour blindness is defective cells in the retina. “We have two types of cells called rods, which are concerned with vision at night or scotopic vision. There are another group called cones, which are concerned with colour vision,” says Dr Paulson.
“There are around 120 million rods in the eye and around six million cones. The cones have three types of pigments — one is concerned with red colour vision, one is concerned with green colour vision and one is concerned with blue colour vision.
“These cone cells respond when they see light at a particular wavelength. In our visible spectrum, the red wavelength comes at around 540 nanometres, so a patient with a defective red cone cell will not be able to appreciate the red colour.”
The level of colour blindness varies from case to case and can be mild, moderate or severe. In some instances, people can see colours but are unable to identify certain shades of a particular colour.
Diagnosis and treatment
Colour blindness needs to be identified at an early age because for some professions, colour vision is very important. Professions such as airline pilots require full colour vision. “We have set tests that can identify colour vision defects. The most common test is the Ishihara test,” says Dr Paulson. This test consists of nine plates and inside certain colours there is a hidden number. With the Ishihara test, the doctor can identify red green colour blindness in patients. A person with good colour vision will read the numbers correctly but a person with defective colour vision will read the numbers differently.
Dr Paulson says that there is no cure for colour blindness but there are treatments available that can improve patients’ ability to differentiate the contrasts between colours. “There are certain types of contact lenses and glasses that are available, which work by improving the contrast between two different colours, so that the patient can identify that a colour could be a shade of red a little better,” she says.
Although the majority of cases of colour blindness are genetic and a child is born with the issue, in some cases it can occur as a result of other health issues. “These are usually problems that occur within the eye, causing an inability to identify certain colours,” says Dr Paulson. “Certain conditions such as optic neuritis [an inflammation that damages the optic nerve], central serous retinopathy and glaucoma can cause colour blindness.”
If your child is colour blind though, it shouldn’t hinder their life too much. “Colour blindness is an easy condition to live with but it can put people at a disadvantage in certain situations. It applies to certain professions and in some countries, people who are colour blind are not permitted to have a driving licence,” says Dr Paulson. “Yet, I know a lot of colour blind people who lead very normal lives.”