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Visual Acuity Scales

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The Visual Acuity conversion chart of Datagraph-med is based on the Journal of Cataract and Refractive Surgery guidelines. Acuities can be entered in 0.02 log mar steps which corresponds to the number of letters read of a 5 letter per row (Bailey-Lovie, ETDRS) chart type. A full line ('20/20') is reported when all letters are red. If one letter of the 20/16 line is read a 20/20+ is recorded. If only 3 letters on the 20/20 line are read correctly a '20/20--' is to be recorded.

The table below shows the chart conversion and available entries. Full 0.1 log mar steps marked in bold.

Logmar

Snellen (ft)

6/6

Decimal

4/4

Jaeger

Niden

Point

-0,30

20/10

6/3

2,0

4/2

 

 

 

-0,28

20/10-

6/3-

2,0p

4/2-

 

 

 

-0,26

20/10--

6/3--

2,0pp

4/2--

 

 

 

-0,24

20/12.5++

6/3.8++

 

4/2,5++

 

 

 

-0,22

20/12.5+

6/3.8+

 

4/2,5+

 

 

 

-0,20

20/12.5

6/3.8

1,60

4/2,5

 

 

 

-0,18

20/12.5-

6/3.8-

1,60p

4/2,5-

 

 

 

-0,16

20/12.5--

6/3.8--

1,60pp

4/2,5--

 

 

 

-0,14

20/16++

6/4.8++

 

4/3,2++

 

 

 

-0,12

20/16+

6/4.8+

 

4/3,2+

 

 

 

-0,10

20/16

6/4.8

1,25

4/3,2

J1+

N2

 

-0,08

20/16-

6/4.8-

1,25p

4/3,2-

 

 

 

-0,06

20/16--

6/4.8--

1,25pp

4/3,2--

 

 

 

-0,04

20/20++

6/6++

 

4/4++

 

 

 

-0,02

20/20+

6/6+

 

4/4+

 

 

 

0,00

20/20

6/6

1,0

4/4

J1

N3

3

0,02

20/20-

6/6-

1,0p

4/4-

J1p

 

 

0,04

20/20--

6/6--

0,9

4/4--

 

 

 

0,06

20/25++

6/7.5++

 

4/5++

 

 

 

0,08

20/25+

6/7.5+

 

4/5+

 

 

 

0,10

20/25

6/7.5

0,8

4/5

J2

N4

4

0,12

20/25-

6/7.5-

0,8p

4/5-

J2p

 

 

0,14

20/25--

6/7.5--

0,8pp

4/5--

 

 

 

0,16

20/32++

6/9.6++

0,7

4/6,3++

 

 

 

0,18

20/30 /32+

6/9 6/9.6+

0,67

4/6,3+

J3

 

5

0,20

20/32

6/9.6

0,63

4/6,3

J4

N6

6

0,22

20/32-

6/9.6-

0,63p

4/6,3-

 

 

 

0,24

20/32--

6/9.6--

0,63pp

4/6,3--

 

 

 

0,26

20/40++

6/12++

 

4/8++

 

 

 

0,28

20/40+

6/12+

 

4/8+

 

 

 

0,30

20/40

6/12

0,5

4/8

J5

N7

7

0,32

20/40-

6/12-

0,5p

4/8-

 

 

 

0,34

20/40--

6/12--

0,5pp

4/8--

 

 

 

0,36

20/50++

6/15++

 

4/10++

 

 

 

0,38

20/50+

6/15+

 

4/10+

 

 

 

0,40

20/50

6/15

0,4

4/10

J6

N8

8

0,42

20/50-

6/15-

0,4p

4/10-

 

 

 

0,44

20/50--

6/15--

0,4pp

4/10--

 

 

 

0,46

20/63++

6/18.9++

 

4/12,6++

 

 

 

0,48

20/60 /63+

6/18 /18.9+

0,33

4/12,6+

J7

 

9

0,50

20/63

6/18.9

0,32

4/12,6

J8

N10

10

0,52

20/63-

6/18.9-

0,32p

4/12,6-

 

 

 

0,54

20/70/63--

6/21 /18.9--

0,29

4/12,6--

 

 

 

0,56

20/80++

6/24++

 

4/16++

 

 

 

0,58

20/80+

6/24+

 

4/16+

 

 

 

0,60

20/80

6/24

0,25

4/16

J9

N11

11

0,62

20/80-

6/24-

0,25p

4/16-

 

 

 

0,64

20/80--

6/24--

0,25pp

4/16--

 

 

 

0,66

20/100++

6/30++

 

4/20++

 

 

 

0,68

20/100+

6/30+

 

4/20+

 

 

 

0,70

20/100

6/30

0,2

4/20

J10

N12

12

0,72

20/100-

6/30-

0,2p

4/20-

 

 

 

0,74

20/100--

6/30--

0,2pp

4/20--

 

 

 

0,76

20/114/125++

6/34.2

0,18

4/25++

J11

 

13

0,78

20/125+

6/37.5+

 

4/25+

 

 

 

0,80

20/125

6/37.5

0,16

4/25

J12

N14

14

0,82

20/125-

6/37.5-

0,16p

4/25-

 

 

 

0,84

20/125--

6/37.5--

0,16pp

4/25--

 

 

 

0,86

20/160++

6/48++

 

4/32++

 

 

 

0,88

20/150 /160+

6/45

 

4/32+

 

 

 

0,90

20/160

6/48

0,13

4/32

J13

N21

21

0,92

20/160-

6/48-

0,13p

4/32-

 

 

 

0,94

20/160--

6/48--

0,13pp

4/32--

 

 

 

0,96

20/200++

6/60++

 

4/40++

 

 

 

0,98

20/200+

6/60+

 

4/40+

 

 

 

1,00

20/200

6/60

0,1

4/40

J14

N23

23

1,02

20/200-

6/60-

0,1p

4/40-

 

 

 

1,04

20/200--

6/60--

0,1pp

4/40--

 

 

 

1,06

20/250++

6/75++

 

4/50++

 

 

 

1,08

20/250+

6/75+

 

4/50+

 

 

 

1,10

20/250

6/75

0,08

4/50

 

 

 

1,12

20/250-

6/75-

0,08p

4/50-

 

 

 

1,14

20/250--

6/75--

0,08pp

4/50--

 

 

 

1,16

20/320++

6/96++

 

4/67++

 

 

 

1,18

20/300 /320+

6/90

0,07

4/67+

 

 

 

1,20

20/320

6/96

0,06

4/67

 

 

 

1,22

20/320-

6/96-

0,06p

4/67-

 

 

 

1,24

20/320--

6/96--

0,06pp

4/67--

 

 

 

1,26

20/400++

6/120++

 

4/80++

 

 

 

1,28

20/400+

6/120+

 

4/80+

 

 

 

1,30

20/400

6/120

0,05

4/80

 

 

 

1,32

20/400-

6/120-

0,05p

4/80-

 

 

 

1,34

20/400--

6/120--

0,05pp

4/80--

 

 

 

1,36

20/500++

6/150++

 

4/100++

 

 

 

1,38

20/500+

6/150+

 

4/100+

 

 

 

1,40

20/500

6/150

0,04

4/100

 

 

 

1,42

20/500-

6/150-

0,04p

4/100-

 

 

 

1,44

20/500--

6/150--

0,04pp

4/100--

 

 

 

1,50

20/600

6/175

0,032

4/120

 

 

 

1,60

20/800

6/200

0,025

4/135

 

 

 

2,00

CF

6/600

0,01

CF

 

 

 

3,00

HM

HM

0,001

HM

 

 

 

Note: You can use any of the scale for data entry and print graphs in a different scale later on. If you normally use the decimal scale and need to make graphs in 20/20 Snellen notation you can switch temporarily to '20/20' in the system tools menu before exporting graphs to PowerPoint. After making the graphs you can switch back to decimal  settings.

HM = 'Hand Movements'; CF = 'Counting Fingers'

Recommended Literature:

VA testing in optometric practice Part 1: The Snellen chart

08/04/05
In this two-part article on visual acuity testing in practice, Professor David Thomson looks into the development and mechanisms of modern day test charts.
David Thomson PhD, BSc, MCOptom
» Download article

 

VA testing in optometric practice
Part 2: Newer chart designs
In Part 2 of this series on visual acuity testing, Professor David Thomson looks at newer test chart designs and possibilities for the future.
David Thomson PhD, BSc, MCOptom
» Download article