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Vision is a measurement of a person’s ability to see clearly unaided (without correction). Standard vision is the ability to read letters that make an angle of one twelfth of one degree at the eye from six metres or twenty feet. If you can see the six metre letter at 6 metres you have 6/6 vision. In America they use feet – hence the term 20/20 vision. It is expressed like a fraction and can also be measured as a decimal or a percentage, hence 6 divided by 6 is 100%.
If you can only see from 6 metres letters you should be able to read at 12 metres then you are said to have 6/12 vision – this “50%” vision is approximately legal driving standard. |