CIRRUS HD-OCT User Manual 2660021169012 Rev. A 2017-12Analysis Related Report Options 10-13measurements. A lavender “Possible Increase” summary box could indicate highmeasurement variability.Apply GPA Results in Context of the PatientGPA reports statistically significant change for one eye, which may or may not be clinicallysignificant. Rate of loss, locations of the detected loss, age of the patient, stage of thedisease, and other clinical factors should be evaluated for clinical decisions. To confirmthat RNFL loss is clinically significant, correlate your results with other clinical tests such asperimetry and IOP.Consider Resetting the Baseline ScansIt is prudent to occasionally review the current Baseline scans and consider changing to amore recent Baseline pair if there has been a significant change in the course of thepatient’s care. A stable period of RNFL thickness may follow a period of RNFL thinning dueto a change in therapy. This leveling off would be a good time to update the Baselineimages. This will allow GPA to flag change from this new point in time instead of havingthe summary flags continuously checked off due to thinning that occurred at an earlier, lessstable time.Statistical SignificanceGuided Progression Analysis compares an observed change with its expected test–retestvariability, as illustrated in Figure 10-11.cáÖìêÉ=NMJNN==aáëíêáÄìíáçå=çÑ=qÉëíÓoÉíÉëí=s~êá~ÄáäáíóStatistically Significant Change from BaselineGuided Progression Analysis compares an observed change with its population test–retestvariability. The test–retest variability was determined by performing an in–houserepeatability and reproducibility study (results reported at ARVO 2008 in a poster, “Inter–Visit and Inter–Instrument Variability for CIRRUS HD-OCT Peripapillary Retinal Nerve FiberCutoff Point for FlaggingPossible Increase (i.e., /2 = 97.5%)Change considered within normal test–retest variability(2.5% to 97.5%)Cutoff Point for FlaggingPossible or Likely Loss(i.e., /2 = 2.5%)Measured RNFL Change
