Snellen Visual Acuity Test
A very common method of measuring a subject’s vision or visual acuity. The test chart consists of lines of letters of varying size and spacing, with the largest letter at the top and a gradual progression down to the smallest letters at the bottom. The test is carried out at a distance of 6 metres and the result is recorded as a Snellen fraction. E.g. 6/9, which suggests that at a distance of 6 metres, the subject is able to see an object with the same clarity as the ‘standard observer’ viewing the same object at a distance of 9 metres.