Zeiss CIRRUS HD-OCT 500, User Manual

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Appendix
2660021169012 Rev. A 2017-12 CIRRUS HD-OCT User Manual
B-20
Table B-18: Repeatability and Reproducibility of Central Corneal Thickness
Comparison of CIRRUS HD-OCT and Ultrasound Pachymetry in Central Corneal
Thickness Measurements
Table B-19 shows the mean difference in central corneal thickness measurements
between CIRRUS HD-OCT and ultrasound pachymetry. The negative difference means that
the CIRRUS CCT measurement is thinner than the ultrasound CCT measurement. This data
was taken from a total of 50 eyes enrolled in one site measured by a single operator for
each device.
Table B-19: Difference in Central Corneal Thickness measurement Between CIRRUS
HD-OCT and Ultrasound Pachymetry
OCT devices in general measure thinner than ultrasound pachymetry. The Visante User
Manual reports an average measurement difference of 15.1
μ m. In the literature, reported
differences between OCT and ultrasound pachymetry range from 11.64 to 49.4 μ m (see
References below).
Performance of CIRRUS HD-OCT RNFL Analysis
Repeatability and Reproducibility
CZMI performed an in–house study on normal subjects to determine the inter–visit and
inter–instrument repeatability of CIRRUS RNFL thickness measurements. The repeatability
and reproducibility (including effects of multiple visits and multiple instruments), along
with the coefficient of variability, are shown in Table B-20 on page B-21. Similar results
were also found in an independent study, which reported a coefficient of variability of
1.5% in normal subjects and 1.6% in patient eyes
2 .
2. Vizzeri, G, Weinreb, RN, Gonzalez-Garcia, AO, Bowd, C, Medeiros, F, Sample, PA, Zangwill, LM: Agreement between spec-
tral-domain and time-domain OCT for measuring RNFL thickness, Br J Ophthalmol, March 2009.
CIRRUS HD-OCT Repeatability CIRRUS HD-OCT Reproducibility Mean Thickness
( μ m)
Repeatability
SD ( μ m)
Repeatability
Limits
a
( μ m)
Reproducibility
SD ( μ m)
Reproducibility
Limits
b
( μ m)
Phase
I
Phase
II
Overall
4.08 11.42 4.23 11.84 544.25 532.25 538.25
a. Repeatability Limit is the upper 95% limit for the difference between repeated results. Per ISO 5725–1 and ISO 5725–6, Repeatability Limit = 2.8 x
Repeatability SD
b. Reproducibility Limit is the upper 95% limit calculated for the difference between results repeated using different operators. Each subject was imaged
three times during a single visit by each of three operators. Per ISO 5725–1 and ISO 5725–6, Reproducibility Limit = 2.8 x Reproducibility SD.
95% CI of the Difference
Mean Difference SD Lower Upper
CIRRUS CCT– Ultrasound
pachymetry CCT (
μ m)
–9.06 5.63 –10.66 –7.46