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Instruction Manual Mesotest II
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4.2. Description of the Unit
Tests for mesopic vision and glare sensitivity
are an important supplement to tests of
photopic visual acuity, especially when
evaluating the ability to drive at night. Pre-
and postsurgical examination is also to be
recommended for patients undergoing IOL
or refractive surgery, or when tinted lenses
are prescribed.
The Mesotest II is a PD-independent, free-
space unit for testing mesopic vision and
glare sensitivity.
"Free-space" means that the test objects
appear under natural visual conditions.
Instrument myopia is eliminated for the most
part, since the eyes accommodate and
converge as in normal vision.
The comfortable, cushioned lining around
the viewing aperture ensures freedom of
viewing and optimum adjustment for all
examinees. The complete elimination of light
from other sources ensures correct
examinations even when room conditions
are only moderately dark.
The ventilation openings of the viewing
aperture lining ensure that condensation
cannot cloud the examinee's glasses or the
unit's occluder.
The test is carried out with optotypes of
different contrast levels. These optotypes
are presented in front of a low-brightness
backdrop.
The light intensity of the backdrop is 0.032
cd/m2 without and 0.10 cd/m2 with glare.
This corresponds to the brightness of
automobile traffic at twilight or at night.
Landolt rings acc. to DIN Norm No. 58220-
T1 are used as optotypes. Since visual
acuity decreases with decreasing
brightness, acuity level 0.1 is used. The
optotypes can be presented in six different
positions, and one position is preselected
automatically at the beginning of each test.
The Landolt ring positions which are
available for selection are:
LO - Top Left
O - Top
RO - Top Right
LU - Bottom Left
U - Bottom
RU - Bottom Right
Four different contrast levels are available.
They are:
1:23 / 1:5 / 1:2,7 / 1:2.
Here contrast level 1:23 corresponds to the
highest contrast, i.e. this level is the most
easily recognized.
Contrast 1:23 is the ratio between light
intensity of the optotypes and the backdrop.
The contrast levels are presented in each
case with and without glare (=BLEND). This
results in a total of eight tests which run
successively during the course of a test
routine.
Table 1 shows the course of the test routine.
Table 1
The viewing screen of the test panel is seen
through an optical system via a
semitransparent viewing mirror. The
optotypes are presented in front of this
viewing screen. Their virtual image appears
at a distance of 5 meters from the eye.
The optotypes are vacuum metallized onto a
glass disk. The projection disk is
manufactured to very tight tolerances for the
various contrast levels.
Test-No. 1 2 3 4 5 6 7 8
Contrast 1:23 1:5 1:2,7
1:2
1:23
1:5
1:2,7 1:2
Glare
Off
Off
Off Off On On On On
Automatic
Land.sett.
LO
RO
O U
RU
U LU O
