Rnfl Thickness Maps And Deviation From Normal Maps - Zeiss CIRRUS HD-OCT 500 User Manual

CIRRUS HD-OCT User Manual
The ONH and RNFL OU Analysis derives the its elements from two kinds of thickness
measurements: along the Calculation Circle and in super-pixels.

RNFL Thickness Maps and Deviation from Normal Maps

RNFL Thickness Maps and Deviation from Normal Maps are all based on calculated
thickness data for the cube as follows:
• RNFL Thickness Maps derive from pixel average thickness measurements and report
thickness using a color pattern, where cool colors (blues, greens) represent thinner
areas and warm colors (yellows, reds) represent thicker areas. The maps exclude the
optic disc, which appears solid blue. The color code expresses thickness ranging from
zero (blue) to 350 μm (white).
• Deviation from Normal Maps derive from super-pixel average thickness measurements
and report the results of a statistical comparison against the normal thickness range
for each super-pixel, overlaid on the OCT fundus image. These maps apply the yellow
and red colors (not the green) of the age-matched normative data to super-pixels
whose average thickness falls in the yellow and red normal distribution percentiles.
The green color of the normative data is not applied because most super-pixels would
be green for normal patients, and the green color might obscure the anatomical detail
in the underlying OCT fundus image. Any region that is not red or yellow falls within or
above normal limits.
A region that is yellow is thinner than all but 5% of normals. A region that is red is
thinner than all but 1% of normals. The deviation map is created by binning individ-
ual pixels of thickness measurement into super-pixels consisting of 16 pixels (4 pixels
or 120 um to a side of each super-pixel). There is a total of 50 by 50 (2500) super-pix-
els analyzed, although super-pixels at the edge or inside of the optic disc are not con-
sidered and not shaded.
There are several reasons why a particular region might differ from normal. The deviation
map shows when a particular region of an eye is thinner than the same region in a
population of normal subjects, but such deviation is not always due to pathological loss of
RNFL, for any of the following reasons:
1. For each super-pixel, 5% of normals will in generally be highlighted yellow, and 1%
of normals will in general be highlighted red. Since each map consists of 2500
super-pixels, 125 pixels on average might be expected to be highlighted on each
normal.
Posterior Segment
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