Impaired vision and blindness are common. About 3.4 million people in the US are blind or visually impaired. Vision is usually measured by visual acuity charts, and normal vision is expressed as 20/20 ...
Colour blindness affects approximately one in 12 men and one in 200 women, which equates to 4.5 per cent of the population or around 2.7 million people in the UK, according to campaign group Colour ...
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