Conversion from Snellen to Logmar

 

 

 

LogMAR

Snellen Equivalent

 

1.0

6/60

0.9

6/48

0.8

6/38

0.7

6/30

0.6

6/24

0.5

6/19

0.4

6/15

0.3

6/12

0.2

6/9.5

*Pass rate for school vision screening

0.1

6/7.5

0.0

6/6

-0.1

6.5

 


 

 

The Snellen Chart, which traditionally has been used to measure visual acuity, is easily recognised as one of the hallmarks of the ophthalmologist's consulting room. More recently, the LogMAR  chart has been introduced into clinical practice. Initially used as a research tool because it is more accurate than other acuity charts, this accuracy is also valuable in the clinical setting and many eye departments now use it routinely. Studies performed on age related macular degeneration (ARMD) utilised LogMAR acuities and therefore, as this research has been translated into practice, most ARMD clinics record vision using this notation.

 

 

 logmar3

 

Testing children’s acuity accurately is always a challenge, but the best charts available now are those utilising LogMAR, for example Sonksen, above. School health nurses are being supplied with logmar testing kits and will be recording in Logmar notation (note many of the newer booklets do not come with a Snellen equivalent scoring notation).

 

 

There can be some difficulty during transition or when some clinics use Snellen and others use LogMAR. Initially conversion is not always intuitive as poorer vision is recorded as a higher number eg 6/60 Snellen is 1.00 LogMAR and 6/6 Snellen is 0.00 LogMAR. This table may help to assist and to ease the understanding of visual acuity measurements.

 

 

Where some letters are not seen on a line of Logmar an extra 0.020 or 0.025 (on a 4 letter display) is added for each missed letter. i.e 0.250 equates to 6/9.5pt. 0.625 equates to 6/24-1.