Colour Vision Deficiency

The term colour deficient is usually used instead of the term colour blind, which implies that no colours can be seen. In colour deficiency, the perception of colour is altered because of an abnormality in the pigments in the retina (back of the eye)

What is colour vision deficiency?

The nerve cells which receive and process light at the back of the eye - the retina - are of two main types: rods which work in dull light and cones which allow us to see fine detail and colours by day. Three different chemicals can be found within the cone nerve cells, so that cone responds to red, green or blue light in a similar manner to colour television. Deficiency is caused by an abnormal cone pigment, usually the one which controls either red or green colours. Defective colour vision can range from near normal, where the chemical within the red or green cones is only slightly altered, to severe where the chemical is altered considerably or in the most severe cases, absent completely. In mild deficiency, only pale colours will be confused unless the lighting is poor or the person is tired or under pressure to make a quick decision of colour name when confusion of deeper hues may occur. Complete colour vision deficiency where all colours are seen as variations of black and white is extremely rare.

Why are more men than women colour deficient?

Defective colour vision may be inherited. A girl's colour vision may be normal, but she can carry the defective gene which can be passed to her children. There is a 50/50 chance a boy will be colour defective if his mother is a carrier of the defective gene, so brothers within the same family can be affected. A girl can only inherit defective colour vision if her father has the problem and her mother is a carrier or herself colour deficient.

Will inherited colour deficiency change with age?

No. The inherited alterations to Colour vision involve both eyes and remain stable through life.

Can you develop colour deficiency?

Yes. Some diseases can cause a colour deficiency, often only in one eye. These include diabetes, multiple sclerosis and cardiovascular diseases (including high blood pressure), some liver diseases and many eye diseases. The colour deficiency is caused by damage to the nerves supplying the cones or the nerve pathways from them to the brain. In these cases, colour vision may be temporarily or permanently altered. Colour discrimination can be affected on its own or may be noticed with other visual problems, such as overall blurring of near or distance vision, or gaps in the field of vision. Women and men are equally at risk. Drugs prescribed for arthritis, malaria, depression and heart disease can, on occasion, significantly impair colour vision. Viagra commonly changes colour vision temporarily, often objects acquiring a blue tint. This is temporary. Long-term use of aspirin has been implicated in colour perception change and tobacco and alcohol taken in excess can have similar effects. Many industrial chemicals can permanently alter our appreciation of colours. Glaucoma, cataract and most eye problems affecting the retina or nerve pathways to the brain can give gradually worsening problems with many different colours, including blues and greens. Since colour vision changes can be an early sign of disease or a side effect of prescribed medication, it is important that you consult your optician or GP if you are aware that your appreciation of colours is changing.

How does colour vision affect normal life?

Some careers do involve some degree of colour identification. Normal colour vision is required to be a pilot or train driver, and companies involved in printing, textiles, paints and electronic components screen prospective employees and may refuse entry for certain jobs if colour perception is not normal. The armed services require normal colour vision for some jobs. The police require a normal colour vision test on application. A colour deficient individual is allowed to drive although there are a few reported cases of accidents caused by people with faulty colour perception driving through a red traffic light. In some countries, law prohibits colour defective people from driving commercial vehicles. It is always sensible to inform teachers if a child is known to have difficulty in identifying colours as colour coding is common.

Can anything be done to correct colour deficiency?

Nothing can replace a faulty mechanism in the retina of the eye - which is essentially a part of the brain - many colour defective people do learn ways of compensating for their difficulty - and indeed are often unaware that they don't see the world in the same way as others, as it has always been that way for them. Good light can help. There is no permanent way of restoring the lost sensation or appreciation of colour, although recent studies have shown some special tinted contact lenses and spectacles can improve colour discrimination when worn.

How is colour vision tested?

Easy tests for defective colour vision are used in the optician's consulting room. These involve reading coloured numbers from a book or following a trail of dots for young children. Some employers require a signal light test (naming of the light colours in order). Optometrists can give such a test as part of an eye examination. Some school medical examinations may include colour vision tests. If a detailed evaluation of colour vision is required, the hospital optometrists have a wider selection of tests available.

I think my child may have a colour vision problem. What should I do?

Book an appointment for an eye examination that includes a test for colour vision. The optometrist will be happy to answer any questions you may have.