What is colour blindness?

Colour blindness is the inability to see certain colours in the normal usual manner. It is also known as colour vision defect. Our eye has an image perception and light sensitive layer that lines the back of eye and is called as retina; it is made up of rod and cone cells. Cone cells are responsible for the colour vision. Any disturbance in the pigment of cone cells causes colour blindness. A person affected is able to see things clearly but misses out some colours. Depending on the number of pigments that are missing an affected person may have difficulty seeing red, green and blue colours or all of the colours. Red-green colorblindness is most common.

What are the different types of colour blindness?

Colour blindness may be genetic or acquired. Normal vision is the ability to use all three types of cone cells for colour perception, it is called as trichromacy. Any anomaly in the colour perception by one type or all of the cone cells causes defective colour perception. Various types are:

• Anomalous trichromacy

  It is the defect in any one type of cone cell. In this type of colorblindness there can be near normal colour vision to total absence of perception of any one type of colour depending on the type of cone cell affected. Protanomaly is the reduced or complete absence of perception to red light; people affected are not able to see red, orange and brown shades. Deuteranomaly is the faulty or no perception of shades of green; it is the most common type of colorblindness. When the defect lies in the perception of shades of blue, it is Tritanomaly. It is the rarest type.

• Dichromacy

  Dichromacy is a kind of colour blindness in which one out of three cones has completely lost the function or are not able to perceive any spectrum of that particular light. When a person has complete absence of red cones than it is called protanopia; when a person has complete absence of green cones than it is called deuteranopia and when a person has complete absence of blue cones than it is called tritanopia.

• Monochromatous vision

  Monochromatous vision commonly known as achromatopsia is a very rare condition in which the person is completely colour blind and is not able to perceive any colour but can only see world in different shades of grey ranging from black and white. Sometimes even if you have been diagnosed with complete colour blindness you should take a second opinion and consult a specialist as the commonly used Ishihara test can be deceptive as it can be a more severe form of red-green colorblindness.

What are the causes of colour blindness?

Colour blindness can be due to many reasons. It can be genetic or acquired due to some medical reasons. Colour blindness that is experienced from birth is generally due to genetic causes. It is x-linked recessive disorder which means it is carried on the x- chromosome. It is more common in males as they have only one x- chromosome. Females are mostly carriers of the disease but disease present itself mostly in those females in which parents had a homozygous marriage meaning marriage between close relatives.

Apart from the genetic causes colour blindness can occur in later life due to ageing and many other causes. Some of the most common causes of colour blindness are diabetes, glaucoma, macular degeneration, Alzheimer’s disease, Parkinsonism, leukaemia, sickle cell anaemia or multiple sclerosis. Certain drugs like digitalis and chloroquine can also cause colour blindness. Any injury or trauma to the eye or accidental exposure to certain noxious chemicals can also be one of the reasons for colour blindness.

What are the symptoms of colour blindness?

The symptoms of colour blindness vary to the amount and kind of colour blindness you have. Skipping lights on a traffic signal is most common on red-green colorblindness. You may not be able to identify many colours from the colour box. You may have problem identifying red, green, blue, purple, pink and yellow shades. Since there is dysfunction of cone cells so there is an increased burden on rod cells which reduces the sharpness of your vision. In complete colour blindness you may only be able to see black, white and shades of grey.

How is colour blindness diagnosed?

Our world is full of colours and colour blindness keeps us away from beautiful colours of life. Since it has a deep impact on your life and what career choice you make. It becomes very important to get it diagnosed at an early age. If your child is in pre-school and has a problem identifying different colours you should consult your health care provider immediately. Your doctor might perform the following tests to make a diagnosis-

• Your doctor might show you a card which is made of coloured dots and you have to identify the alphabet or number in those dots. These are of different types and helps diagnose different types of colour blindness.
• Your doctor might also show you some coloured chips which you have to arrange. People who are colour blind are not able to do so.

What is the treatment for colour blindness?

At present there is no treatment for colour blindness. There are some lenses that market themselves as an aid in colour blindness but their efficacy has not been proven. It may also have an effect with sharpness and depth of vision. Since rods are overburdened they are affected by bright light, it is also advisable for affected individuals to wear tinted glasses as it may help reduce load on rod cells.