7
8
0.5
10
0.3
=1.995′
9
0.6
10
0.2
=1.585′
10
0.8
10
0.1
=1.259′
11
1
10
0
=1.000′
12
1.2
10
-0.1
=0.794′
13
1.5
10
-0.2
=0.631′
14
2.0
10
-0.3
=0.501′
1.3.3.2 C chart, 123 chart and animal chart
Fig 3. Chart
C chart adopts Landolt ring. The width of the black ring and the gap both are 1/5 of the ring’s
outer diameter, as shown in picture 3 above.
1.3.3.2.1 C chart scale and dimension
Scale and dimension for C chart at 5m test distance is shown in below tables.
Table 2 Scale and dimension for C chart 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′
