DICOM PS3.17 2019a - Explanatory Information

RR.2.5 ETDRS Charts

ETDRS charts feature Sloan letters with proportional spacing, 5 letters on each line, and a logarithmic progression of letter sizes with consistent increments of approximately 25% per line (10 lines equal a factor 10x). The ETDRS protocol specifies letter-by-letter scoring, viewing distance, illumination, use of different charts for right and left eye and other presentation parameters.

The full ETDRS protocol requires a wide chart on a light box, and cannot be implemented on the limited screen of a projector (or similar) chart. The logarithmic progression, however, can be implemented on any device. This progression was first proposed by John Green in 1868 and follows the standard "Preferred Numbers, ISO standard 3 (1973) " series and the rounding preferences.

Use of ETDRS charts allows use of letter-by-letter scoring, which is more accurate than the line-by-line scoring used on traditional charts. Each row in the table is equivalent to 1 letter on an ETDRS chart (50 letters for a factor 10x). These steps are smaller than the just discernible difference; steps this small only become significant in statistical studies where a large number of measurements is averaged.

The smaller steps for letter by letter scoring may be expressed in two ways; either by using suffixes to a familiar (sometimes slightly rounded) set of values or by using calculated values. For clinical use suffixes have the advantage of using only familiar acuity notations and reverting to the nearest clinical notation when the suffix is omitted. Calculated values look less familiar; but are sometimes used in statistical studies. Note that suffixes used in the context of an ETDRS chart have a defined value and affect the DICOM storage value, whereas suffixes used in the context of traditional charts do not.

Table RR-2. Reference Table for Use with ETDRS Charts or Equivalent

DICOM

Notations for Research Use with ETDRS Charts or Equivalent

Scales for statistics and graphical displays

Decimal Visual Acuity

Use with suffixes

Calculated values

Linear Scales

Decimal

US

6 m

Decimal

US

6 m

LogMAR

VAS

2.00 E+00

2.0

20/10

6/3

2.00

20/10

6/3.0

-0.30

115

1.91 E+00

-

-

-

1.91

20/10.5

6/3.2

-0.28

114

1.82 E+00

- -

- -

- -

1.82

20/11

6/3.3

-0.26

113

1.74 E+00

+ +

+ +

+ +

1.74

20/11.5

6/3.5

-0.24

112

1.66 E+00

+

+

+

1.66

20/12

6/3.6

-0.22

111

1.60 E+00

1.6

20/12.5

6/3.8

1.58

20/12.5

6/3.8

-0.20

110

1.50 E+00

-

-

-

1.51

20/13

6/4.0

-0.18

109

1.45 E+00

- -

- -

- -

1.45

20/14

6/4.2

-0.16

108

1.38 E+00

+ +

+ +

+ +

1.38

20/14.5

6/4.4

-0.14

107

1.30 E+00

+

+

+

1.32

20/15

6/4.6

-0.12

106

1.25 E+00

1.25

20/16

6/4.8

1.26

20/16

6/4.8

-0.10

105

1.20 E+00

-

-

-

1.20

20/17

6/5.0

-0.08

104

1.15 E+00

- -

- -

- -

1.15

20/17.5

6/5.2

-0.06

103

1.10 E+00

+ +

+ +

+ +

1.10

20/18

6/5.5

-0.04

102

1.05 E+00

+

+

+

1.05

20/19

6/5.8

-0.02

101

1.00 E+00

1.0

20/20

6/6

1.00

20/20

6/6.0

0

100

9.55 E-01

-

-

-

0.95

20/21

6/6.3

0.02

99

9.00 E-01

- -

- -

- -

0.91

20/22

6/6.6

0.04

98

8.70 E-01

+ +

+ +

+ +

0.87

20/23

6/6.9

0.06

97

8.30 E-01

+

+

+

0.83

20/24

6/7.2

0.08

96

8.00 E-01

0.8

20/25

6/7.5

0.79

20/25

6/7.5

0.10

95

7.50 E-01

-

-

-

0.76

20/26

6/7.9

0.12

94

7.20 E-01

- -

- -

- -

0.72

20/28

6/8.3

0.14

93

7.00 E-01

+ +

+ +

+ +

0.69

20/29

6/8.7

0.16

92

6.60 E-01

+

+

+

0.66

20/30

6/9.1

0.18

91

6.30 E-01

0.63

20/32

6/9.5

0.63

20/32

6/9.5

0.20

90

6.00 E-01

-

-

-

0.60

20/33

6/10.0

0.22

89

5.75 E-01

- -

- -

- -

0.58

20/35

6/10.5

0.24

88

5.50 E-01

+ +

+ +

+ +

0.55

20/36

6/11.0

0.26

87

5.25 E-01

+

+

+

0.52

20/38

6/11.5

0.28

86

5.00 E-01

0.5

20/40

6/12

0.50

20/40

6/12.0

0.30

85

4.80 E-01

-

-

-

0.48

20/42

6/12.5

0.32

84

4.57 E-01

- -

- -

- -

0.46

20/44

6/13.2

0.34

83

4.37 E-01

+ +

+ +

+ +

0.24

20/46

6/13.8

0.36

82

4.17 E-01

+

+

+

0.42

20/48

6/14.5

0.38

81

4.00 E-01

0.4

20/50

6/15

0.40

20/50

6/15.1

0.40

80

3.80 E-01

-

-

-

0.38

20/52

6/15.8

0.42

79

3.60 E-01

- -

- -

- -

0.36

20/55

6/16.6

0.44

78

3.50 E-01

+ +

+ +

+ +

0.35

20/58

6/17.4

0.46

77

3.33 E-01

+

+

+

0.33

20/60

6/18.2

0.48

76

3.20 E-01

0.32

20/63

6/19

0.32

20/63

6/19.1

0.50

75

3.00 E-01

-

-

-

0.30

20/66

6/20.

0.52

74

2.90 E-01

- -

- -

- -

0.29

20/69

6/21

0.54

73

2.75 E-01

+ +

+ +

+ +

0.28

20/72

6/22

0.56

72

2.63 E-01

+

+

+

0.26

20/76

6/23

0.58

71

2.50 E-01

0.25

20/80

6/24

0.25

20/79

6/24

0.60

70

2.40 E-01

-

-

-

0.24

20/83

6/25

0.62

69

2.30 E-01

- -

- -

- -

0.23

20/87

6/26

0.64

68

2.20 E-01

+ +

+ +

+ +

0.22

20/91

6/28

0.66

67

2.10 E-01

+

+

+

0.21

20/95

6/29

0.68

66

2.00 E-01

0.2

20/100

6/30

0.20

20/100

6/30

0.70

65

1.90 E-01

-

-

-

0.191

20/105

6/32

0.72

64

1.82 E-01

- -

- -

- -

0.182

20/110

6/33

0.74

63

1.74 E-01

+ +

+ +

+ +

0.174

20/115

6/35

0.76

62

1.66 E-01

+

+

+

0.166

20/120

6/36

0.78

61

1.60 E-01

0.16

20/125

6/38

0.158

20/126

6/38

0.80

60

1.50 E-01

-

-

-

0.151

20/132

6/40

0.82

59

1.45 E-01

- -

- -

- -

0.145

20/138

6/42

0.84

58

1.38 E-01

+ +

+ +

+ +

0.138

20/145

6/44

0.86

57

1.30 E-01

+

+

+

0.132

20/151

6/46

0.88

56

1.25 E-01

0.125

20/160

6/48

0.126

20/158

6/48

0.90

55

1.20 E-01

-

-

-

0.120

20/166

6/50

0.92

54

1.15 E-01

- -

- -

- -

0.115

20/174

6/52

0.94

53

1.10 E-01

+ +

+ +

+ +

0.110

20/182

6/55

0.96

52

1.05 E-01

+

+

+

0.105

20/191

6/58

0.98

51

1.00 E-01

0.1

20/200

6/60

0.100

20/200

6/60

1.00

50

9.55 E-02

-

-

-

0.095

20/210

6/63

1.02

49

9.00 E-02

- -

- -

- -

0.091

20/220

6/66

1.04

48

8.70 E-02

+ +

+ +

+ +

0.087

20/230

6/69

1.06

47

8.30 E-02

+

+

+

0.083

20/240

6/72

1.08

46

8.00 E-02

0.08

20/250

6/75

0.079

20/250

6/76

1.10

45

7.50 E-02

-

-

-

0.076

20/260

6/79

1.12

44

7.20 E-02

- -

- -

- -

0.072

20/280

6/83

1.14

43

7.00 E-02

+ +

+ +

+ +

0.069

20/290

6/87

1.16

42

6.60 E-02

+

+

+

0.066

20/300

6/91

1.18

41

6.30 E-02

0.063

20/320

6/95

0.063

20/315

6/95

1.20

40

6.00 E-02

-

-

-

0.060

20/330

6/100

1.22

39

5.75 E-02

- -

- -

- -

0.058

20/350

6/105

1.24

38

5.50 E-02

+ +

+ +

+ +

0.055

20/360

6/110

1.26

37

5.25 E-02

+

+

+

0.052

20/380

6/115

1.28

36

5.00 E-02

0.05

20/400

6/120

0.050

20/400

6/120

1.30

35

4.80 E-02

-

-

-

0.048

20/420

6/126

1.32

34

4.60 E-02

- -

- -

- -

0.046

20/440

6/132

1.34

33

4.40 E-02

+ +

+ +

+ +

0.044

20/460

6/138

1.36

32

4.20 E-02

+

+

+

0.042

20/480

6/145

1.38

31

4.00 E-02

0.04

20/500

6/150

0.040

20/500

6/151

1.40

30

3.80 E-02

-

-

-

0.038

20/520

6/158

1.42

29

3.60 E-02

- -

- -

- -

0.036

20/550

6/166

1.44

28

3.50 E-02

+ +

+ +

+ +

0.035

20/575

6/174

1.46

27

3.33 E-02

+

+

+

0.033

20/600

6/182

1.48

26

3.20 E-02

0.032

20/630

6/190

0.032

20/630

6/191

1.50

25

3.02 E-02

-

-

-

0.030

20/660

6/200

1.52

24

2.90 E-02

- -

- -

- -

0.029

20/690

6/210

1.54

23

2.75 E-02

+ +

+ +

+ +

0.028

20/720

6/220

1.56

22

2.63 E-02

+

+

+

0.026

20/760

6/230

1.58

21

2.50 E-02

0.025

20/800

6/240

0.025

20/800

6/240

1.60

20

2.40 E-02

-

-

-

0.024

20/830

6/250

1.62

19

2.30 E-02

- -

- -

- -

0.023

20/870

6/260

1.64

18

2.20 E-02

+ +

+ +

+ +

0.022

20/910

6/280

1.66

17

2.10 E-02

+

+

+

0.021

20/950

6/290

1.68

16

2.00 E-02

0.020

20/1000

6/300

0.0200

20/1000

6/300

1.70

15

1.90 E-02

-

-

-

0.0191

20/1050

6/315

1.72

14

1.82 E-02

- -

- -

- -

0.0182

20/1100

6/330

1.74

13

1.74 E-02

+ +

+ +

+ +

0.0174

20/1150

6/350

1.76

12

1.66 E-02

+

+

+

0.0166

20/1200

6/363

1.78

11

1.60 E-02

0.016

20/1250

6/380

0.0158

20/1250

6/380

1.80

10

1.50 E-02

-

-

-

0.0151

20/1300

6/400

1.82

9

1.45 E-02

- -

- -

- -

0.0145

20/1380

6/420

1.84

8

1.38 E-02

+ +

+ +

+ +

0.0138

20/1450

6/440

1.86

7

1.30 E-02

+

+

+

0.0132

20/1500

6/460

1.88

6

1.25 E-02

0.0125

20/1600

6/480

0.0126

20/1600

6/480

1.90

5

1.20 E-02

-

-

-

0.0120

20/1660

6/500

1.92

4

1.15 E-02

- -

- -

- -

0.0115

20/1740

6/520

1.94

3

1.10 E-02

+ +

+ +

+ +

0.0110

20/1820

6/550

1.96

2

1.05 E-02

+

+

+

0.0105

20/1910

6/575

1.98

1

1.00 E-02

0.010

20/2000

6/600

0.0100

20/2000

6/600

2.00

0


DICOM PS3.17 2019a - Explanatory Information