• Question: why can't you see colours when your colour blind ?

    Asked by claire13 to Indi, Jarv, John, Ken, Vicky on 11 Mar 2012.
    • Photo: John Prytherch

      John Prytherch answered on 9 Mar 2012:

      Ahh, this should be a good question for me because I am colour blind. Unfortunately I don’t know much biology. I think that there are a number of reasons that people can be colour blind, which is partly why some colour blind people see in actual black and white, and others, like me, just can’t distinguish different colours very well.
      I think the most common reason is a problem with the “cones” in the eye. These are one of the light receptors at the back of the eye (the other type is called rods) that are used to recognise different colours.

      I expect one of my fellow scientists knows more about this and can tell us both more…

    • Photo: Indi Ghangrekar

      Indi Ghangrekar answered on 11 Mar 2012:

      As John said, there is a problem with the “cones” in the eye – one type of cell in the human eye that can sense light. Vision is a result of detecting light with your eyes and sending that information to the brain that makes sense of it.

      In human eyes, there are 5 different types of cells that detect light using similar proteins called opsins, which is just the term for light detecting proteins. The 4 commonly known cells are rods and 3 different types of cones – red, green and blue. The rods don’t detect different colours but can just sense light of any colour and are very sensitive, they’re mostly used when there is not a lot of light available, like at nighttime and vision with just rods would be in black and white. The 3 different types of cones detect the 3 different colours. When a mixture of the cone types detect light, you can see a bigger range of colours than red, green and blue. People that are colour blind either have one or more cone type missing or the light detecting protein in one or more of their cones is not working the same way as most other peoples’. I don’t know all the different types of colour blindness but as John said some people will only see black and white, whereas others may not be able to distinguish different colours very well. It is actually quite common.

      The 5th type of light detecting cell in the eye is quite a bit different to rods and cones and does not contribute to vision but to some other functions that are sub-conscious, for example, change in size of the pupil because of bright or dim lighting. It also sends information to the body clock about time of day! That’s why, even though the body clock mostly detects what the time of day is by sensing the amount of light, it may lead you to guess that blind people do not have a working body clock but in fact most blind people do! Another research lab that some friends of mine work in here at my university study this cell, it has quite a long convoluted name – melanopsin retinal ganglion cell.

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