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PostĆrun editing of axial length measurements
The results of axial length measurements must be interpreted on the
basis of the signalĆtoĆnoise ratio and the appearance of the graphs
(
cf.Ă
"Example signal curves of axial length measurements"
, p.53
).
The illustrations below do not contain the video image.
Fig. 43 Presentation of the graph of the fifth axial length measurement (23.00 mm;
SNR: 6.6) on the right eye (shown without video image)
SNR categories
While the system is internally calculating the axial length from the
interference signal, it automatically analyzes the SNR.
SNR > 2.0 --> The measured value is valid.
SNR in the range 1.6 ... 2.0 --> The measured value is not reliable
(Fig. 44)
The signalĆtoĆnoise ratio may be low for the following reasons:
Ć Dense medial opacity along the visual axis,
Ć restless patients,
Ć alignment of instrument to patient eye is not optimal,
Ć very high ametropia (> 6 D),
Ć corneal scars,
Ć retinal pathology.
Fig. 44 Non reliable value
Evaluation of ALM results
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