Sub-Rpe Considerations - Zeiss CIRRUS HD-OCT 500 User Manual

8-19
Posterior Segment
The possible impact of such pathologies on the analysis can be taken into account by
reviewing the individual B-scans and determining where areas of RPE elevation overlap
with them.
As with all retinal pathology, check the retinal segmentation in questionable cases. View
the horizontal tomogram and check the black and lavender lines indicating the borders of
the RPE elevation measurement.
The RPE Elevation algorithm has not been tested on subjects who had geographic atrophy,
choroidal neovascularization, or pigment epithelial detachments. The performance of the
RPE Elevation algorithm on subjects with these conditions has not been determined. Since
pigment epithelial detachments are elevations to the RPE, the Advanced RPE Analysis may
be of clinical use. See Appendix Appendix B "CIRRUS Algorithm Studies" for the
performance of Advanced RPE Analysis measurements.
Repeatability of measurements of RPE elevation are dependent on consistent and accurate
identification of the fovea location. The system has an automatic fovea finder. Make sure
the software was able to find the fovea location and evaluate if the location is correct (see
"Fovea Location" on page 8-6). If the location is determined not to have been
correct, the patient should be rescanned using a manual correction.
The minimum RPE elevation that the software will include in the quantitative result is
19.5 μm. Values below this threshold are not included in the area and volume calculations.
In some cases, drusen may be observed in color Fundus photographs that are not seen in
the Advanced RPE Analysis because either the drusen does not represent any elevation, or
because the drusen is accompanied by an elevation that does not meet the minimum
threshold for detection. Only small, shallow drusen are likely to be missed.
NOTE: RPE elevation measurements are not meant to replace other means of clinical
evaluation such as color Fundus photographs for drusen documentation and
measurement.
Sub–RPE Considerations
The Sub–RPE slab represents the summed reflectivity in the region below Bruch's
membrane. This slab indicates the fovea location with a dot and a circle corresponding to 5
mm in diameter centered on the fovea. It also shows a red line from the fovea to the
closest area with sub–RPE illumination (label 6 in Figure 8-12).
The automatic sub–RPE illumination segmentation is shown with an outline. The
boundaries can be toggled on or off. If the sub–RPE illumination segmentation outlines are
toggled on, these will become transparent to the same degree as the sub–RPE slab.
The Advanced RPE Analysis includes a horizontal tomogram. This tomogram shows the RPE
elevation segmentation lines, but not the segmentation lines for the sub–RPE slab
segmentation. The segmentation lines may be toggled on or off.
Increased sub–RPE illumination is not specific to geographic atrophy and can occur in any
condition that causes RPE atrophy or thinning, absence or breaks, such as retinal
dystrophies, scarring due to infections, and laser photocoagulation of the retina. In
CIRRUS HD-OCT User Manual 2660021169012 Rev. A 2017-12