Maxine,
Snellen charts are marked on the front or back with the distance that they
are used at; 1.5,3 and 6m are the usual in UK. US charts are in feet - so
20 feet is 6 metres.
A simple explanation of the Snellen system (in US) is
http://www.visionforlife.com/understand/acuity.htm
Another explanation of how the chart adapts at 10 feet (3m) is
http://www.i-see.org/eyecharts.html
There is a recent paper in the BMJ that looks at how effective Snellen is at
mimicking the results of the "number plate test" used by DVLA
http://www.bmj.com/cgi/content/full/321/7267/990?
In basic terms 6/9 is the same as 3/18 if using a 3m chart. This is the
same as 20/30 in US measurement. You just go back to basic maths, and
"vulgar" fractions.
Dr. Geoff Helliwell MB ChB CIH FFOM MIOSH
Medical Director
WellWork Ltd. UK
-----Original Message-----
From: Occ-health is a list open to everyone with an interest in
teaching, learning [mailto:[log in to unmask]]On Behalf Of Maxine
Taylor
Sent: 29 June 2001 16:34
To: [log in to unmask]
Subject: Visual Acuity Standard
On behalf of a colleague undertaking Fork Lift Truck driver assessents,
what is the 6/9 acuity standard equivalent if using a snellen chart at 3
metres? Thanks Maxine.
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