Visual test?

Question

I am wondering what does that 3 rows of visual test means, i mean from the 1st row which is big characters to the 3rd rows which is relatively small. how did the nurse deduce 6/6, 6./7.5 to 6/120 etc?

Any additional helpful information on this particular test will be most helpful. Many thanks!

Answer 1

The chart has various letters made in standard sizes for standard test distances. Standard test distance is 6 metres. The smallest letter the average human eye without eye disease can see subtends about 1 degree in arc. The "6" size letter subtends 1 degree if viewed from 6 metres, the "7.5" subtends 1 degree if viewed from 7.5 metres, the "120" subtends 1 degree at 120 metres and so on.

Your visual acuity is recorded as the smallest size you are able to correctly read at the standard 6 metre test distance. So if you could read the "6" line you have 6/6 vision, if you could only read the "120" line you have 6/ 120. The nurse doesn't have to deduce anything, she records the letter size.

Answer 2

I guess anything before 20/20, you might need glasses/contacts. But 20/20 is perfect vision. It is rare to get higher then 20/20.