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Eye Diseases

Colour Vision

Colour vision is possible due to photoreceptors in the retina of the eye known as cones. These cones have light sensitive pigments that enable us to recognize colour. Found in the macula, the central portion of the retina, each cone is sensitive to red, green or blue light, which the cones recognize based upon light wavelengths.

Normally, the pigments inside the cones register differing colour and send that information through the optic nerve to the brain enabling you to distinguish countless shades of colour. But if the cones lack one or more light sensitive pigments, you will be unable to see one or more of the three primary colours thereby causing a deficiency in your colour perception.

Colour vision deficiency is the inability to distinguish certain shades of colour or in more severe cases, see colours at all.

There are instances where one cannot see colour at all, these are said to be colour blind, meaning that they can only see things as black and white or in shades of grey. This condition is called achromatopsia.

It is possible for a person to have poor colour vision and not know it. Early detection of colour deficiency is vital since many learning materials rely heavily on colour perception or colour coding.

Most people with colour vision deficiency can see colours, but they have difficulty differentiating between

Type of colour deficiency
  • Red-green deficiency
  • Blue-yellow deficiency

This is a less common but more severe form of colour vision than red-green since the patients with blue-yellow deficiency frequently have red-green blindness also.

People with colour deficiencies are likely to see neutral or grey areas where a particular colour should appear.

The severity of colour vision deficiency can range from mild to severe depending on the cause.
  • It will affect both eyes if it is inherited
  • One if the cause for the deficiency is due to injury or illness.

Causes of colour deficiency

  • Usually an inherited condition, caused by a common X-linked recessive gene, which is passed from a mother to her son
  • Disease and injury damaging the optic nerve or retina can also result in colour recognition loss.
Some specific diseases that can cause colour deficiency include:

Diabetes Alzheimer's disease
Glaucoma Parkinson's disease
Macular degeneration Multiple sclerosis
Leukaemia Sickle cell anaemia

Other causes for colour vision deficiency include:

Chronic alcoholism Aging Chemical Exposure e.g. fertilizers and styrene
Medications: such as drugs used to treat heart problems, high blood pressure, infections, nervous disorders and psychological problems

Diagnosis and Treatment of Colour vision

Colour deficiency can be diagnosed through a comprehensive eye examination. Testing will include the use of a series of specially designed pictures composed of coloured dots, called pseudisochromatic plates, which include hidden numbers or embedded figures that can only be correctly seen by persons with normal colour vision.

There is no cure for inherited colour deficiency. Furthermore should the colour vision deficiency be as a result of a disease or eye injury, treating the conditions may improve colour vision.

The use of special tinted spectacles, such as red tinted contact lens can enhance the colour differentiation. Although nothing can make you truly see the deficient colour.

Compensatory mechanisms

People with colour deficiency can make use of cues and details that are not consciously evident to people with normal colour vision, such can be:
  • Organizing and labelling clothing, furniture or other coloured objects (with the help of friends or family) for ease of recognition.
  • Remembering the order of things rather than their colour can also increase the chances of correctly identifying colours. For example a traffic light has red on top, yellow in the middle and green on the bottom.
Colour vision deficiency can be a frustration and may limit participation at work and school, in most cases it is not a serious threat to vision and can be adapted to your lifestyle with time, patience and practice. Click here for Colour Vision Test