An eyesight score of 6/12 is your visual acuity test result based on the Snellen Scale eye chart. The second number on the visual acuity score (in this instance it’s 12) is based on a person with normal vision and that doesn’t require corrective vision. This means that a person with normal vision can read a specific line of text from an eye chart from 12 metres.
If you have a visual acuity score of 6/12, it means you can read the same line of text from a distance of 6 metres – half that of a person with normal eyesight.
For another example, if we consider the top largest letter on the eye chart, if a person can only read this letter from a distance of 6 metres and none of the smaller letters, their visual acuity score will be 6/60. It means they they can read this letter from 6 metres distance, whereas a person with normal eyesight can read the same letter from a distance of 60 metres.