When evaluating glaucomatous progression over time, Cirrus contains the most complete glaucoma progression analysis software, according to Dr. Schuman. Data obtained from the extracted circumpapillary scan provide the average, superior, and inferior RNFL thicknesses and a statistical analysis that describes if there is a significant difference from “no change” in the regression line.
The changes in average cup-to-disc ratio are analyzed, and RNFL thickness profiles over time and on a specific day are provided analyzed for change over time. Another nice feature is a table of numerical values of the parameters for each visit with significant changes emphasized.
The Spectralis provides a serial analysis of progression, the results of which are depicted in graphs from a patient’s scan. No statistical program is included to document significant progression changes.
The Optovue provides changes in both the ganglion cell count (GCC) and the RNFL thickness. The changes in RNFL thickness are documented in a graph from baseline to the current day; the significant changes in the GCC are highlighted in a table. For both parameters, the device provides a statistical test for trend. “With each machine, when the RNFL becomes very thin, there is a floor effect, that is, the point at which the instrument can no longer measure the RNFL or the GCC,” Dr. Schuman cautioned.
“Clinicians must be careful and not be fooled into thinking that the patient is stable, when in fact the RNFL is so thin that the machine cannot determine that the glaucoma is worsening.”