Posterior Segment2660021169012 Rev. A 2017-12 CIRRUS HD-OCT User Manual8-32The earliest two exams are treated as baseline exams (Baseline 1 and Baseline 2). The lateror follow–up exams (3rd exam through last exam) are compared to the baselines to see ifthey have changed. All scans, including the Baseline 2, are registered to the first Baseline 1in order to ensure accurate correspondence from the first scan to the last scan. The averageRNFL 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 twomethods. First, it attempts to use method R2, which is based on the blood vesselsidentified in theen face images of both scans. Method R2 uses translation and rotation toalign 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 bepossible because the blood vessels will not line up well enough. In this case, the center ofthe optic disc from the follow–up scan translated to the center of the optic disc of the firstscan prior to making comparisons for the purposes of identifying change. This method iscalled 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 assessedthrough evaluating changes in several clinical factors, including optic nerve headappearance and visual fields. GPA only refers to change in the Nerve Fiber Layer orGCL+IPL thickness assessed by statistical analysis of certain CIRRUS parameters. Suchchanges in thickness may or may not be related to clinically relevant changes. GPA is notmeant to diagnose. Diagnosis is the responsibility of the practitioner, who should basediagnosis on many parameters, including those not assessed by CIRRUS.Parameter Summary GraphsParameter Summary graphs ("GCL+IPL Summary Graphs" on page 8-39 forGanglion Cell, "RNFL & ONH Parameter Summary Graphs" on page 8-35 forRNFL) identify global thinning in the Retinal Nerve Fiber layer or the Ganglion Cell layer bycalculating a trend over time. Statistically significant loss or improvement, based oncomparisons to test-retest variability, is also reported by color-coding the markers for eachvisit. The Average Thickness Graphs are calculated by averaging large portions of theprofile - this is why they detect only global loss. Each chart displays parameter data from 3to 8 exams plotted in chronological order. The individual points are highlighted to indicatewhen the value plotted has changed from baseline by an amount more than the test–retestvariability. Possible loss is indicated when the rate of loss is statistically significant for onlya single visit and is indicated by a yellow symbol. Likely loss is indicated when the rate ofloss 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 shownvia a lavender symbol. Possible increase should only occur due to random fluctuations ordue to problems with scan quality.
