6 Device Description
Instruction Manual Mesotest II (G/62800/0715/en) 15 / 86
Testing mesopic vision To adapt the test conditions to the luminance conditions prevailing on
roads at night, the Landolt ring is presented on a test field with a
luminance of 0.032 cd/m², and for the test with glare, on a test field with
a luminance of 0.1 cd/m².
During the function test, unlike in the visual acuity test, the size of the
Landolt ring is not reduced, but rather the contrast that it has to its
surroundings. The size of the Landolt ring corresponds with a visual acuity
of 0.1. Four different contrast levels are available for reducing the
contrast.
1:23
1:5
1:2.7
1:2
The contrast level 1:23 is the strongest contrast, i.e. this level is the
easiest to see.
Testing mesopic vision with glare Testing of mesopic vision can also be conducted with additional glare. The
glare comes from the left, just as it would in a road traffic situation.
Thresholds according to DOG (Ger-
man Ophthalmological Society)
The following thresholds for assessment of fitness for driving in road
traffic are recommended by DOG and the German Association of
Ophthalmologists:
Classes D, D1, DE, D1E: Contrast 1:2,7
Classes C, C1, CE, C1E and taxi drivers: Contrast 1:5
Classes A, A1, A2, B, BE, AM, L and T: Contrast 1:23
A stop criterion similar to that described in DIN 58 220 (visual acuity test)
must be established as the test criterion: 3 out of 5 of the different
optotypes presented must be correctly recognised. This means that for the
critical contrast levels 1:23 to 1:2.7, at least 5 different optotypes must
be presented.
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