Zeiss CIRRUS HD-OCT 500, User Manual

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CIRRUS HD-OCT User Manual 2660021169012 Rev. A 2017-12
Appendix
A-23
Axial Length and Refractive Error
Figure A-14 below shows a plot of Ganglion Cell Analysis Average Thickness versus axial
length of the study eye. It can be seen that GCL + IPL thickness decreases slightly as a
function of axial length. This contributes less than 2% of the total variability of the
Ganglion Cell Analysis parameters.
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Data Analysis
The same analysis model was used as was used for the Macular Thickness normative data
analysis, see
"RNFL and Macula Normative Databases: Diversified" on page
A-1 .
A regression model analysis was used to estimate the normative limit of each of the
Ganglion Cell Analysis parameters adjusted by age. The subject's age is considered as a
clinically important factor for the ganglion cell plus inner plexiform layer thickness
measurements.
For each fitted regression model, the residuals were derived for each eye by subtracting the
estimated expected mean reading, ET(age0), from the measured or observed reading,
Obs(age0). In other words, residual = Obs(age0) – ET(age0). The goal was to predict the
100x

th
percentiles (NL, normative limit) of the residuals, so that the 100x

% limit of the
CIRRUS HD-OCT parameter readings could be estimated as follows:
ET(age0) + NL(100x

%) < Obs(age0) (A)
The 1st, 5th, 95th, and 99th percentiles of the residuals were estimated by the empirical
distribution of residual. Then the estimated 1%, 5%, 95% and 99% normal limits of
CIRRUS HD-OCT parameters for a normal subject with an age of age0 were established by
Equation (A). It should be noted that the study site effect was not considered in the
normative limits calculation since the objective was to establish the normative limits for the
general population.