Colour Vision Deficiency

Definition
Failure of a person to identify a colour or a whole range of colour is termed as colour vision deficiency or colour blindness. In true words it means failure to see any colour but this condition is very rare and can be confused to complete blindness.
Types of colour blindness:
Colour blindness is common in men affecting 1 in 20 where as it is rare in women affecting 1 in 200.
There are basically three types of colour blindness:
Deuteranopia- Red green deficiency: Most common where the affected person have difficulty in distinguishing different shades of red and green.
Tritanopia-Blue yellow deficiency: it is a rare condition where yellow might appear as pale grey.
Achromatopsia-Total colour blindness: Extremely rare where no colours will be detected and the affected person sees everything in shades of black.
Causes:
The cells present in the retina are the reason why we can appreciate the colour. The cells are known as cones and they interpret colour by being able to analyse 3 primary colours red, green and blue. Using these colours the cones are able to identify hundreds of different shades and hues of the colour.
When the light enters the eye it passes through the layers of the eye and reaches the cones where certain chemicals interact which will send signal to brain where the different colour is appreciated.
The cause of colour vision deficiency is due to lack of some of the colour sensitive chemicals that is needed for the colour interpretation.
The main causes are:
Inherited colour vision deficiency
Colour vision deficiency is usually an inherited disease, which is passed on through certain genes; it might affect only one colour or all the three primary colours.
Other medical conditions: some of the medical conditions might affect the colour vision of the eye resulting in colour vision defect. The most common colour deficiency is
Glaucoma: where the pressure of the eye is increased resulting in damage to optic nerve.
Macular degeneration: Chronic eye disease resulting in blindness,
Diabetes retinopathy: Where the retina is affected which destroys the cells in the retina.
Leukaemia.
Alcoholism
Sickle cell anaemia; where the RBC which is sickle shaped obstructs the blood supply to the eye.
Alzheimer’s disease.
Parkinson’s disease.
Medications are associated with loss of colour vision as they might be toxic, if the colour vision deficiency is caused by drugs, the vision will return to normal. Medicines given to treat
Heart problems
High blood pressure.
Infections.
Nervous disorders.
Psychological problems.
When one person is exposed to toxic chemicals they are prone to develop colour vision deficiency. Chemicals like
Carbon disulfide.
Fertilisers.
Styrene
Diagnosis: Most people will become aware they are suffering from colour deficiency as they might struggle to read certain documents or prints printed in certain colour. The doctor diagnosis colour deficiency by the standard Ishihara plate test, where plates containing 16 different pictures made up of multiple colours are shown and the test is done for both the eye by closing one at a time.