Table of Contents
Advertisement
8-32
2660021169012 Rev. A 2017-12
Posterior Segment
The earliest two exams are treated as baseline exams (Baseline 1 and Baseline 2). The later
or follow–up exams (3rd exam through last exam) are compared to the baselines to see if
they have changed. All scans, including the Baseline 2, are registered to the first Baseline 1
in order to ensure accurate correspondence from the first scan to the last scan. The average
RNFL thickness value is displayed for each exam above its corresponding thickness map.
There is an indication above each displayed exam to describe the registration performed.
Prior to comparing scans, CIRRUS registers them to the first baseline scan using one of two
methods. First, it attempts to use method R2, which is based on the blood vessels
identified in the
en face
images of both scans. Method R2 uses translation and rotation to
align the follow-up scan to the baseline scan.
If there is motion in either the baseline or the follow–up scans, the R2 method may not be
possible because the blood vessels will not line up well enough. In this case, the center of
the optic disc from the follow–up scan translated to the center of the optic disc of the first
scan prior to making comparisons for the purposes of identifying change. This method is
called R1. It does not include rotation.
If the R1 method is used, you may observe additional variability at the super-pixel level.
This may affect detection of change in the Map.
NOTE: CIRRUS does not evaluate "progression of glaucoma", which can only be assessed
through evaluating changes in several clinical factors, including optic nerve head
appearance and visual fields. GPA only refers to change in the Nerve Fiber Layer or
GCL+IPL thickness assessed by statistical analysis of certain CIRRUS parameters. Such
changes in thickness may or may not be related to clinically relevant changes. GPA is not
meant to diagnose. Diagnosis is the responsibility of the practitioner, who should base
diagnosis on many parameters, including those not assessed by CIRRUS.
Parameter Summary Graphs
Parameter Summary graphs
Ganglion Cell,
"RNFL & ONH Parameter Summary Graphs" on page 8-35
RNFL) identify global thinning in the Retinal Nerve Fiber layer or the Ganglion Cell layer by
calculating a trend over time. Statistically significant loss or improvement, based on
comparisons to test-retest variability, is also reported by color-coding the markers for each
visit. The Average Thickness Graphs are calculated by averaging large portions of the
profile - this is why they detect only global loss. Each chart displays parameter data from 3
to 8 exams plotted in chronological order. The individual points are highlighted to indicate
when the value plotted has changed from baseline by an amount more than the test–retest
variability. Possible loss is indicated when the rate of loss is statistically significant for only
a single visit and is indicated by a yellow symbol. Likely loss is indicated when the rate of
loss is statistically significant for two visits in a row and is indicated by a red symbol.
Possible increase is indicated when the rate of gain is statistically significant and is shown
via a lavender symbol. Possible increase should only occur due to random fluctuations or
due to problems with scan quality.
("GCL+IPL Summary Graphs" on page 8-39
for
for
CIRRUS HD-OCT User Manual
Advertisement
Table of Contents
Troubleshooting
