Leica DM2500, Manual

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64
10. Measurements with the Microscope
10.3 Differentiation of Gout / Pseudo Gout
The use of the lambda plate compensator is a
prerequisite for this test.
Assembly
→
p. 31.
Orienting the Lambda Plate Compensator
• Rotate the lambda plate compensator out of
the light path (Fig. 67).
• Bring the lambda plate compensator and
analyzer into cross position until they reach
maximum darkness (polarization
→
p. 59).
• Fix the cross position thus determined with
the clamping screw at the side (67.2).
• Swing in the lambda plate again.
The following section explains the basic proce-
dure for gout/pseudo gout differentiation. This
test is made possible due to the negative
birefringence of urates and positive
birefringence of pyrophosphates. Both gout
(monosodium urate) and pseudo gout (calcium
pyrophosphate) crystals tend to be needle
shaped. However, many crystals may be broken
and/or irregular. To do the test, it is necessary to
find at least one intact crystal orientated on
same axis as orientation handle and one per-
pendicular to axis.
Procedure
To insure the test is being done correctly, a slide
of known monosodium urate crystals should be
used initially.
• Use of a 40x objective is recommended.
• Swing the lambda plate out of the path of light
(fig. 67).
• Place the slide on the stage and bring the
crystals into sharp focus. The needle shaped
crystals will appear white regardless of orien-
tation.
• Swing in the lambda plate and put the orienta-
tion handle (67.1) in its extreme left position.
Crystals with a long dimension in the handle
direction should appear yellow, and perpen-
dicular to handle direction should appear
blue (fig. 68).
Fig. 67 Lambda plate compensator swung out
1 Orientation handle
2 Clamping screw
2
1
90
°