Zeiss CIRRUS HD-OCT 500, User Manual

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CIRRUS HD-OCT User Manual 2660021169012 Rev. A 2017-12
Criteria for Image Acceptance
7-9
overlaid on the B-scan in Figure 7-6 F . There are no normal vessels at the level of the RPE,
so the vasculature seen in the
en face
in Figure 7-6 C is entirely due to decorrelation tails.
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This effect is always weaker than the original signal, and is also correlated with the
brightness of the reflecting layer. Therefore, decorrelation tails may appear to have
disappeared within the outer nuclear layer, but then appear strongly again in the brightly
reflecting RPE.
Figure 7-6 C clearly shows that an
en face
image collected only around the
RPE includes vasculature very similar to the overlying SRL. There are two potential ways to
determine whether a signal is due to decorrelation tails or due to motion in the layer
observed. One is the characteristic of the vasculature itself, even if it is disrupted. A typical
normal eye demonstrates that the deeper retinal layer (
Figure 7-6 E ) has a different
characteristic appearance than the superficial retinal layer ( Figure 7-6 D ). Another way is
to note when the vessel of interest has exactly the same shape as a layer superior to it. The
area around the RPE is not expected to have any vasculature, so the
en face shown in
Figure 7-6 C is clearly due to decorrelation tails.
Segmentation Errors
Segmentation errors can result in incorrect visualization of flow. The boundary lines used to
determine the particular
en face
image shown appear as magenta dotted lines overlying
A: SRL En Face B: DRL En Face C: Above the RPE En Face
SRL segmentation
D: B-scan showing E: B-scan showing
DRL segmentation F: B-scan showing
segmentation above the RPE