Quality of vision / visual acuity

We measure the quality of vision or V/A (visual acuity) using a sight test chart.  The smaller the letters that  one can read on the chart the better the visual acuity

Normal Vision ...

Normal vision is achieved when letters which are designed just to be read at 6 metres can be read at this distance.  A person with poorer vision, e.g. the right eye in the example, can just see letters at 6 metres which a normal eye can see further away at 12 metres. This is still quite good vision,. To pass a driving test, an acuity of slightly better than 6/12 is necessary

Typical sight test chart

N  A  O  K  B

F   Z   M   D   E

K   A   R   M   C    B    H

E   A   U   B   G   P   F   N

E  H  R  B

Z A S

HA

H