Zeiss CIRRUS HD-OCT 500, User Manual

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CIRRUS HD-OCT User Manual 2660021169012 Rev. A 2017-12
Appendix
B-15
Study 4: Repeatability and Reproducibility of GCA and ONH Parameters
A study was conducted to determine the repeatability and reproducibility of the Ganglion
Cell Analysis (GCA) and Optic Nerve Head (ONH) parameters. Sixty–three (63) subjects
were enrolled in this study that was performed in two phases. Phase 1 was inter–operator
testing, where four operators (A, B, C, and D) acquired measurements on one CIRRUS
HD-OCT unit (C1). The order of the operators used for scanning each subject was
determined using a randomization table. For each subject, a series of twelve (12)
RNFL/ONH scans were taken for one eye and twelve (12) macular thickness scans were
taken for the fellow eye for a total of 24 scans. Each of the four operators acquired 3 scans
per eye on one CIRRUS 4000 unit. Phase 2 was inter–device testing where four CIRRUS
HD-OCT units (C1, C2, C3, C4) were operated by a single operator (A). The order of devices
used for each subject was randomized.
Table B-14 presents the repeatability and reproducibility standard deviation (SD) and
limits for the CIRRUS HD-OCT. Among the GCA parameters, the minimum thickness had the
largest repeatability limit and reproducibility limit (8.0165
μ m and 8.1018 μ m respectively)
and the average thickness had the smallest repeatability limit and reproducibility limit
(1.6348
μ m and 2.0942 μ m respectively). The repeatability of the minimum thickness
measurement was notably lower than the rest of the parameters; this is expected as the
minimum thickness is a more variable measurement from subject to subject, depending
upon disease severity.
Among the ONH parameters, the disc area measurement had the largest repeatability limit
(0.1506 mm
2
) and the smallest repeatability limit was the cup volume measurement
(0.0181 mm
3
). The largest reproducibility limit was for the disc area (0.0942 mm
2
) and the
smallest reproducibility limit was for the cup volume measurement (0.0102 mm
3
). The
reproducibility limits will affect the ability to determine when measurements have change
due to a change in pathology as opposed to random variability.
The optic nerve head algorithm may show increased variability in certain anatomical
variants. For tilted discs and discs with large clusters of blood vessels, shadowing of the
underlying RPE and Bruch's membrane may render the disc edge difficult to identify.
Variability may also be increased due to ambiguity in cup marker placement for small,
crowded discs with shallow cups, and discs with large clusters of blood vessels. Cups with
excavation or embryonic tissue remnants may have variable cup volume measurements.
The coefficient of variation (CV) was also determined for the CIRRUS HD-OCT GCA and
ONH parameters. Among the GCA parameters, the minimum thickness had the largest CV
of 2.5% and the average thickness had the smallest CV of 0.7%. Among the ONH
parameters, the cup volume measurement had the largest CV of 7.8% and the smallest CV
was the rim area of 4.7%.