Zeiss CIRRUS HD-OCT 500, User Manual

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CIRRUS HD-OCT User Manual 2660021169012 Rev. A 2017-12
Appendix
A-33
The Cup to Disc Ratio (Average and Vertical) as well as the Cup Volume, showed
differences among ethnicity groups (mean difference for both ACDR and VCDR was 0.06,
p = 0.012, mean difference in Cup Volume was 0.04 mm
3
, p = 0.03).
Results revealed that the mean difference in the average GCL + IPL thickness between any
two race groups is within 2.5 mm. Indians have thinner GCL + IPL thickness on average,
while Chinese have thicker (p = 0.02).
Calculation of Normal Limits
As with the post–hoc analysis of the original normative databases, analysis of the ONH
parameters for the Asian normative data found that these parameters depend on both
optic disc area of the subject eye and subject age. A linear fit is used to model the age
effects. The variability of parameters such as Rim Area and Cup to Disc Ratio on Disc Area
was found to depend on the size of the disc. For this reason, quantile regression was used
rather than linear regression to set the limits on the ONH parameters with respect to Disc
Area. This is a method whereby the slope and offset are independently fit for each limit.
See
Artes and Crabb
3 for a description of quantile regression.
Conclusion
The CIRRUS HD-OCT Asian RNFL, macular thickness, ONH, and Ganglion Cell Analysis
Normative Databases were created using data from subjects that were deemed
representative of a normal population. The CIRRUS HD-OCT Asian Normative Database for
RNFL thickness established reference values for the Optic Disc Cube 200x200 scan. The
Macula Asian Normative Database established reference values for the Macular Cube
512x128 and Macular Cube 200x200 scans. Post–hoc analysis was used to develop
reference values for Ganglion Cell Analysis and ONH as well. The doctor can use these
normative databases to compare individual patient measurements to those acquired in a
normal population.