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This makes it difficult to tell the difference between shades of blue and green. Blue–yellow colour vision deficiencyĬhanges in the OPN1SW gene cause blue-yellow colour vision deficiency. In males, there is not another copy of the gene to compensate for the genetically changed copy. In females, a functional gene on only one of the two X chromosomes is sufficient to produce normal colour vision. Males have only one X chromosome and females have two. This is because the genes that lead to red–green colour vision deficiency blindness ( OPN1LW and OPN1MWI) are on the X chromosome (they are ‘sex-linked’). It occurs in about eight per cent of males and only about 0.4 per cent of females. Red–green colour vision deficiency is the most common inherited type. OPN1SW is on chromosome 7.Ĭolour vision problems can also arise later in life due to disease, trauma or exposure to toxins. The OPN1LW and OPN1MW genes are on the X chromosome. The genes involved are OPN1LW, OPN1MW and OPN1SW. It occurs due to a change in one (or more) of three genes that are involved in the production of visual photopigments (known as opsins). What causes colour vision deficiencyĬolour vision deficiency is most commonly a genetic condition. Parents may find signs of colour vision deficiency when children are learning to name the colour of objects. The signs that your child may have a colour vision difficulty include trouble recognising and identifying different colours or an inability to separate things by their colour. Symptoms of colour vision deficiency in children Someone who has colour vision deficiency lacks one or more of these types of cone cells, or may have an altered response due to a genetic change or eye disease. By comparing the responses from the three types of cones, the visual system of the brain produces the wide range of colours that most people see. Usually, there are three types of cone cell, which respond to long (red), medium (green) and short (blue) wavelengths of light. There is only one type of rod cell.Ĭone cells react to brighter light and help us to see detail in objects. We use rod cells to see things around us at night, but only in shades of black, grey and white. In the retina, at the back of the eye, the two types of cells are rod cells and cone cells. Eye cells and visionĪll the cells and nerve pathways in the eye and brain are present from birth. They may confuse red and green with each other or with yellow. In the most common form of colour vision deficiency, people cannot see the red and green components of colours. People who can't see all colours can still see some colours, and will see other things, such as fine detail, as clearly as people with full colour vision. The term colour vision deficiency is more accurate than the term ‘colour blind’. Out of 20 males, it is likely that one or two will have a colour vision problem. Colour vision deficiency is often inherited, and affects more males than females. People who have a colour vision deficiency have difficulty seeing some colours or see them differently from other people.