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000000Ć1150Ć839 IOLMaster 11.02.2004
Signals from the inner limiting membrane (ILM)
Measuring light is relatively often reflected at the inner limiting
membrane thus also producing an interference signal. The corresponĆ
ding ILM signal peak appears to the left of the measuring peak for the
RPE by a distance of 0.15 Ć 0.35 mm. If the measuring cursor is placed
at the ILM it will produce a shorter innacurate axial legth value by 0.15
to 0.35 mm. This is the most likely reason that no average axial length
value is generated for a series. In the zoomed view of the measuring
curve, both peaks may be clearly distinguished from each other
(Fig. 49).
Fig. 49 Double peak produced at inner limiting membrane (left) and RPE (right)
(triple zoom)
RPE
ILM
Usually, the signal from the amplitude of the peak produced by the inner
limiting membrane is smaller than that of the reflectance from the
pigmented epithelium. In such a case the automatic algorithm finds the
correct axial length.
Note:
Never move the measuring cursor manually to the (left) peak
produced by the inner limiting membrane!
In rare cases it may happen that the amplitude of the signal from the
inner limiting membrane is higher than that of the reflected light from
the pigmented epithelium. In this case automatic peak detection will
place the cursor incorrectly at the peak from the ILM.
Fig. 50 Signal curve with higher signal from inner limiting membrane (left peak)
(double zoom)
RPE
ILM
In measurement series such individual measurements stand out by
deviations in the range of approx. 0.15 Ć 0.35 mm towards shorter axial
lengths. You may correct the measured value by moving the measuring
cursor to the right to the smaller peak (that produced by the pigmented
epithelium). This manipulation is permissible only with the other signal
curves of this measurement series!
Evaluation of ALM results
