Tab.1 - Degree of difficulty of Sloan letters (% CORRECTED AT THRESHOLD)
|
# |
S |
O |
C |
D |
K |
V |
R |
H |
N |
Z |
|
% |
70.6 |
71.0 |
71.4 |
79.5 |
82.1 |
84.6 |
86.3 |
89.3 |
91.6 |
94.0 |
Tab.2 Distance test, 4 m (20 ft)
Conversion table (sizes in steps of 0.1 logUnit)
|
Snellen Ratio |
Decimal Acuity |
M.A.R. |
log. M.A.R. |
Stroke Size |
Optotype Size |
Relative Size |
||||||||
|
4 m. |
20 ft. |
Decimal ratio |
|
min. of arc |
log Unit |
mm. |
mm. |
x |
||||||
|
4/40 |
20/200 |
1/10 |
0.10 |
10 |
1.0 |
11.64 |
58.20 |
40 |
||||||
|
4/32 |
20/160 |
1.2/10 |
0.12 |
7.94 |
0.9 |
9.24 |
46.23 |
32 |
||||||
|
4/25 |
20/125 |
1.6/10 |
0.16 |
6.31 |
0.8 |
7.34 |
36.72 |
25 |
||||||
|
4/20 |
20/100 |
2/10 |
0.20 |
5.01 |
0.7 |
5.83 |
29.17 |
20 |
||||||
|
4/16 |
20/80 |
2.5/10 |
0.25 |
3.98 |
0.6 |
4.63 |
23.17 |
16 |
||||||
|
4/12.6 |
20/63 |
3.2/10 |
0.32 |
3.16 |
0.5 |
3.68 |
18.40 |
12.6 |
||||||
|
4/10 |
20/50 |
4/10 |
0.40 |
2.51 |
0.4 |
2.92 |
14.62 |
10 |
||||||
|
4/8 |
20/40 |
5/10 |
0.50 |
1.99 |
0.3 |
2.32 |
11.61 |
8 |
||||||
|
4/6.3 |
20/32 |
6.5/10 |
0.65 |
1.58 |
0.2 |
1.84 |
9.22 |
6.3 |
||||||
|
4/5 |
20/25 |
8/10 |
0.80 |
1.25 |
0.1 |
1.47 |
7.33 |
5 |
||||||
|
4/4 |
20/20 |
10/10 |
1.00 |
1 |
0.0 |
1.16 |
5.82 |
4 |
||||||
|
4/3.2 |
20/16 |
12/10 |
1.20 |
0.79 |
- 0.1 |
0.92 |
4.62 |
3.2 |
||||||
Tab.3 Near chart, 40 cm (16 inch).
Conversion Table (sizes in steps of 0.1 logUnit)
|
Equivalent Snellen Ratio (metres) |
Snellen Ratio (centimetres) |
Snellen Ratio (inches) |
Decimal acuity |
Log. MAR |
Sloan M system |
|
4/100 |
40/1000 |
20/500 |
0.04 |
1.4 |
10 |
|
4/80 |
40/800 |
20/400 |
0.05 |
1.3 |
8.0 |
|
4/60 |
40/600 |
20/300 |
0.06 |
1.2 |
6.4 |
|
4/50 |
40/500 |
20/250 |
0.08 |
1.1 |
5.0 |
|
4/40 |
40/400 |
20/200 |
0.10 |
10 |
4.0 |
|
4/30 |
40/300 |
20/150 |
0.13 |
0.9 |
3.2 |
|
4/25 |
40/250 |
20/125 |
0.15 |
0.8 |
2.5 |
|
4/20 |
40/200 |
20/100 |
0.20 |
0.7 |
2.0 |
|
4/16 |
40/160 |
20/80 |
0.25 |
0.6 |
1.6 |
|
4/12 |
40/120 |
20/60 |
0.30 |
0.5 |
1.25 |
|
4/10 |
40/100 |
20/50 |
0.40 |
0.4 |
1.0 |
|
4/8 |
40/80 |
20/40 |
0.50 |
0.3 |
0.8 |
|
4/6 |
40/60 |
20/30 |
0.65 |
0.2 |
0.6 |
|
4/5 |
40/50 |
20/25 |
0.80 |
0.1 |
0.5 |
|
4/4 |
40/40 |
20/20 |
1.00 |
0.0 |
0.4 |
|
4/3 |
40/30 |
20/15 |
1.30 |
-0.1 |
0.3 |
Tab.3b Sloan M System conversion
|
Equivalent Snellen Ratio (metres) |
Snellen Ratio (centimetres) |
Decimal acuity |
Log. MAR |
Sloan M system |
|
4/100 |
40/1000 |
0.04 |
1.4 |
10 |
|
4/80 |
40/800 |
0.05 |
1.3 |
8.0 |
|
4/60 |
40/600 |
0.06 |
1.2 |
6.4 |
|
4/50 |
40/500 |
0.08 |
1.1 |
5.0 |
|
4/40 |
40/400 |
0.10 |
10 |
4.0 |
|
4/30 |
40/300 |
0.13 |
0.9 |
3.2 |
|
4/25 |
40/250 |
0.15 |
0.8 |
2.5 |
|
4/20 |
40/200 |
0.20 |
0.7 |
2.0 |
|
4/16 |
40/160 |
0.25 |
0.6 |
1.6 |
|
4/12 |
40/120 |
0.30 |
0.5 |
1.25 |
|
4/10 |
40/100 |
0.40 |
0.4 |
1.0 |
|
4/8 |
40/80 |
0.50 |
0.3 |
0.8 |
|
4/6 |
40/60 |
0.65 |
0.2 |
0.6 |
|
4/5 |
40/50 |
0.80 |
0.1 |
0.5 |
|
4/4 |
40/40 |
1.00 |
0.0 |
0.4 |
|
4/3 |
40/30 |
1.30 |
-0.1 |
0.3 |
Tab.4 Percentage of the identifications corrected
for guessingby mean of Abbott Formula
.|
Number of optotypes (n) |
Number of presentations (N) |
Number of mistakes (M) |
% of identifications (I) |
% of correct identifications (CI) |
|
4 |
4 |
1 |
75% |
66% |
|
4 |
5 |
1 |
80% |
73% |
|
4 |
6 |
2 |
60% |
46% |
|
4 |
7 |
2 |
71% |
62% |
|
10 |
5 |
2 |
60% |
55% |
|
10 |
7 |
2 |
71% |
68% |
Tab.5 - Low vision.
Conversion table logMAR/Snellen ratio.
|
Distance |
Log.MAR |
Snellen ratio |
||
|
(meters)
|
Log Units |
4 meters |
20 feets |
Decimal ratio |
|
4 |
1.0 |
4/40 |
20/200 |
1/10 |
|
3,2 |
1.1 |
4/50 |
20/250 |
1/12 |
|
2,5 |
1.2 |
4/63 |
20/320 |
1/16 |
|
2,0 |
1.3 |
4/80 |
20/400 |
1/20 |
|
1,6 |
1.4 |
4/100 |
20/500 |
1/25 |
|
1,3 |
1.5 |
4/125 |
20/630 |
1/30 |
|
1,0 |
1.6 |
4/160 |
20/800 |
1/40 |
|
0,8 |
1.7 |
4/200 |
20/1000 |
1/50 |
|
0,6 |
1.8 |
4/250 |
20/1250 |
1/62 |
|
0,5 |
1.9 |
4/320 |
20/1600 |
1/80 |
|
0,4 |
2.0 |
4/400 |
20/2000 |
1/100 |