Analysis Protocols
Stratus OCT User Manual PN 2660021134133 A
6-30
• Rate of change (slope): The reported rate of change is the best unbiased estimate of
the slope, or rate of change, based on the given points. Stratus reports the rate of
change in units of micrometers per year (μ/yr).
• Confidence range: Stratus also reports the range of slopes that are consistent with the
data with 95% confidence. The true slope may be larger or smaller than the best
estimate that Stratus reports, but there is 95% confidence that the slope is inside the
region given by the slope +/- the confidence range. For example, if the regression
result reported by Stratus is:
Rate of change: -4.5 micrometers/year +/- 3 µ/year
then there is 95% confidence that the rate of change of average RNFL thickness is
between -7.5 micrometers per year and -1.5 micrometers per year.
• Statement of significance: When the confidence bounds include zero, the regression
result text reports that the rate of change is
Statistically not significant,
because there is not 95% confidence that the slope is decreasing. Stratus also reports
Statistically not significant when the best unbiased estimate of the slope is
positive, because increasing RNFL thickness is not consistent with glaucomatous
damage.
When the slope is negative and the 95% confidence range does not include zero,
then there is 95% confidence that a decreasing trend of RNFL thickness exists. Stratus
will then report that the rate of change is
Statistically significant with P < 5%,
because there is less than a 5% probability that the negative slope occurred by
chance.
WARNING: Because scan variability depends on image quality factors such as
signal strength and scan placement, it is possible to observe a statistically
significant slope that does not indicate glaucomatous progression. Carefully
examine the profiles, the scan quality factors, the scans themselves, and all
other clinical information that is available before making a judgment about
whether a patient is experiencing glaucomatous loss of RNFL.
Stratus will also calculate the 99% and 99.9% confidence ranges. If the 99% confi-
dence range does not include zero, and the slope is negative, then the significance
statement regarding the rate of change will be
Statistically significant with P <
1%
. If the 99.9% confidence range does not include zero, and the slope is negative,
then the significance statement will be
Statistically significant with P < 0.1%.
Retinal Thickness
Application: Select Retinal Thickness to obtain graphs of retinal thickness for any scan.
Retinal Thickness analyzes one scan group of any scan protocol at a time, except (Fast)
Optic Disc. Normative data will appear in the output if you analyze a Fast Macular
Thickness Map (Fast Mac) scan, as described in Macula Normative Database on
page 6-7.
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