6
1.3.2.1 Charts visiual test range
Visiual test results will be displayed in decimals, including 14 types including 0.1,
0.12, 0.15, 0.2, 0.25, 0.3, 0.4, 0.5, 0.6, 0.8, 1.0, 1.2, 1.5, 2.0 etc.
1.3.2.2 Number of charts
Lines represents results about 0.2 must contain no less than 3 charts.
1.3.3 Chart specification
1.3.3.1 E chart
1.3.3.1.1 Shape of E chart
E chart single letter overall shape is a square that can be devided into 3 equal
parts, and each line and the gaps between 2 lines must be 1/5 of the length of the
square side. As shown in below picture:
Fig 2. E chart
1.3.3.1.2 Scale and dimension of E chart
When test at 5m, the scale and dimension of E chart requirements is shown in
below table:
Table 1. E chart scale and dimension at 5m
NO. Visual acuity / Decimal
（
V
）
Ratio
（
visual angle α(′)
）
1
0.1
10
1
。
0
=10.000′
2
0.12
10
0.9
=7.943′
3
0.15
10
0.8
=6.310′
4
0.2
10
0.7
=5.012′
5
0.25
10
0.6
=3.981′
6
0.3
10
0.5
=3.162′
7
0.4
10
0.4
=2.512′
