How is colour vision tested?
Colour vision defects can be simply tested by recording discriminated patterns or numbers on the Ishihara colour vision plates and sometimes further diagnosis oocurs in specially equiped colour vision clinics. Defective colour vision is not ‘colour blindness’ and is common and inherited.
1 in 12 men (8 percent)
1 in 200 women (0.5%)
Present at birth and remains unchanged.
There is no treatment but different techniques to allow colour to be inferred by brightness are being researched and developed. Sometimes tints can be used to select more specific wavelenghts but will not cure colour vision defects. Typically greens, yellows, oranges and reds can be confused. It causes colour matching problems,colour naming problems and inability to perceive brightness of colours.
How is colour vision graded?
Colour is used in schools for teaching purposes so all children should have their colour vision tested
Ishihara test,which is very reliable and only takes a few minutes.
> 3 errors means fail.
Follow up is necessary.
Defects can vary in severity. The Ishihara test doesn’t measure the extent of the defect.
By preschool a child may show signs of having problems with recognition and identification of different colours.
What causes colour vision defects?
Accidents and trauma to the retina or brain can cause defects and acquired colour defects can be important in pathology diagnosis.
Nutritional causes such as deficiency of vitamin A and degenerative diseases of the eye – macular degeneration, glaucoma,diabetes and cataracts can all bear on the quality of colur vision.
Inherited colour blindness is the most common cause due to loss, or partial loss of the different cone systems within the eye due to missing or damaged genes.
Further tests are required to assess this provided by an optometrist sometimes in specially equiped colour vision clincs featuring such equipment such as the Nagel anomaloscope, D15 test where hue samples are recorded and referenced in a juxtaposed fashion to a reference and the Farnsworth lantern.
The Ishihara test doesn’t measure the extent of the defect.
Further tests are required to assess this.
Follow up can be provided by an optometrist or ophthalmologist.
The rod cells are active in low light and the cone cells (active in normal daylight) . A normal eye has three kinds of colour receptors.
For red, green and blue light Responses are relayed to the brain.
Here they are mixed together to perceive many thousands of colours.
Defects occur by:
One receptor is missing.
One receptor is abnormal.
Two or even three receptors are missing is more rare and a more serious problem.
Colour vision and your job
Everyday problem examples of coping with a colour vision defect:
Recognising colour of traffic lights.
Seeing coloured flowers on trees.
Judging ripeness of fruit.
Knowing when meat is cooked.
Job requirements where colour vision could be an issue
eg Airline pilot
Air traffic controller
Train and tram driver
Careers in the defence forces
What is the most common colour vision defect?
Red-green colour blindness is by far the most common type of colour defect because the genes that lead to red-green colour blindness are on the X chromosome with males having just one X chromosome, whilst females have two.
Blue colour blindness is far less common, being present in just 5% of all colour blindness sufferers. The genes affected are equal in both sexes.