Transcript Background - ASCRS/ASOA 2011

Comparison of the combined placido discScheimpflug and the Scheimpflug-only imaging
systems for the assessment of anterior segment
Yakov Goldich MD, Reut Singer MD, Cornelius Nasser MD,
David Zadok MD, Isaac Avni MD
Department of Ophthalmology
Assaf Harofeh Medical Center
Israel
The authors have no conflicts of interest and no financial interest in the article’s subject matter or methods mentioned.
Background
•Corneal topography and thickness are
important in diagnosing and evaluating
progression of corneal ectatic disorders.
Background
•
•
The Sirius topography system
(CSO, Italy) is a new device
that uses the combination of
two, 360-degree rotating
Scheimpflug cameras and a
Placido disk principles.
It provides, in a single scan,
anterior segment imaging and
measurements, anterior and
posterior corneal topography,
complete corneal pachymetry
and wavefront analysis.
Purpose
• The purpose of this study was to report
our initial experience with the Sirius
topography system, to assess
repeatability of its measurements and to
assess the agreement with Pentacam's
(Oculus, Germany) measurements.
Methods
•
•
In this prospective study, we examined one
eye of consecutive 45 healthy subjects
(mean 40.23 ± 10.49 years, 21 male and
24 female).
The anterior and posterior corneal
curvature (ACR, PCR) at 3mm and 7mm,
anterior chamber depth (ACD) and minimal
corneal thickness (MCT) were evaluated.
Methods
•
Evaluation of the repeatability of the Sirius was performed
by calculating the coefficient of variation (CV).
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•
CV was defined as the SD of the difference from the mean of the
repeat measurements divided by the mean response.
For each measured parameter we calculated the coefficients of
variation of each one of the subjects.
The mean of these coefficients of variation was defined as the
mean coefficient of variation of the specific parameter.
Assessment of the agreement between the Sirius and the
Pentacam was performed by calculating the 95% limits of
agreement (LoA) and plotting Bland-Altman graphs.
Results
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Repeatability
Mean coefficients of variation were as follow:
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0.37% for anterior corneal radius at 3mm
1.32% for posterior corneal radius at 3mm
0.36% for anterior corneal radius at 7mm
1.28% for posterior corneal radius at 7mm
1.69% for the minimal corneal thickness
0.56% for the anterior chamber depth
Results
Mean measurement values with Pentacam and Sirius
Anterior corneal radius(mm)
Posterior corneal radius(mm)
Anterior chamber depth(mm)
Thinnest corneal point(µm)
Pentacam
Sirius
mean difference
P value
7.73±0.26
7.72±0.26
0.018
0.019
6.42±0.27
6.53±0.36
-0.1
0.001
2.91±0.31
2.97±0.29
-0.068
<0.001
11.91
<0.001
548.52±34.14 536.6±32.94
Anterior radius of curvature pair
difference in mm (Pentacam-Sirius)
Results
0.15
0.1
0.05
0
-0.05
-0.1
-0.15
-0.2
7
7.5
8
Mean of Pentacam and Sirius (mm)
8.5
FIGURE 1. Bland Altman plot for anterior corneal radius measured by
Sirius and Pentacam. The dashed line represents the mean
difference and the solid lines represent the 95% LoA. The 95% LoA
were 95% LoA were -0.1 to 0.12 mm (mean difference 0.018mm)
Posterior radius of curvature pair difference
in mm (Pentacam-Sirius)
Results
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1
-1.2
-1.4
6
6.5
7
7.5
8
Mean of Pentacam and Sirius (mm)
FIGURE 2. Bland Altman plot for posterior corneal radius measured by
Sirius and Pentacam. The dashed line represents the mean
difference and the solid lines represent the 95% LoA. The 95% LoA
were -0.54 to 0.33 mm (mean difference 0.1mm)
Anterior chamber depth pair
difference in mm (Pentacam - Sirius )
Results
0.2
0.1
0
-0.1
-0.2
-0.3
-0.4
-0.5
-0.6
2
2.5
3
3.5
4
Mean of Pentacam and Sirius
(mm)
FIGURE 3. Bland Altman plot for anterior chamber depth measured by
Sirius and Pentacam. The dashed line represents the mean
difference and the solid lines represent the 95% LoA. The 95% LoA
were -0.23 to 0.09 mm (mean difference 0.068mm)
Results
Minimal corneal thickness pair
difference in µm (PentacamSirius)
60
50
40
30
20
10
0
-10
-20
400
500
600
700
Mean of Pentacam and Sirius (µm)
FIGURE 4. Bland Altman plot for thinnest corneal point measured by
Sirius and Pentacam. The dashed line represents the mean
difference and the solid lines represent the 95% LoA. The 95% LoA
were -9.61 to 33.44 µm (mean difference 11.91µm)
Conclusions
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The Sirius showed good to excellent repeatability for all
measured parameters.
The observed agreement with Pentacam for each
parameter should be considered for each particular clinical
application.
The clinician should determine whether the difference
between the two devices is clinically significant.
We recommend these devices should not be used
interchangeably.
Correspondence: Yakov Goldich MD, E-mail: [email protected]