1. Comparison of corneal powers obtained from four different devices
Mariko Shirayama, M.D, Li Wang, M.D, PhD,
Mitchell P. Weikert, M.D, Douglas D. Koch, M.D.
Cullen Eye Institute, Baylor College of Medicine, Houston, TX.
Financial Interest Disclosure: Research support--Li Wang;
travel expenses--Douglas D. Koch

2. Purpose
To assess the repeatability and comparability of corneal powers obtained from the
Galilei Dual Scheimpflug Analyzer
Humphrey Atlas corneal topographer
IOLMaster
Manual keratometer

3. Methods Prospective study Corneal power measurements by 4 methods
All 4 devices use a refractive index of to convert anterior corneal curvatures into an estimate of average total corneal power:
Galilei Dual Scheimpflug Analyzer: SimK
Humphrey Atlas corneal topographer: SimK
IOLMaster: corneal power
Manual keratometer (Bausch & Lomb)

4. Subjects Corneas measured with: Inclusion criteria:
4 devices
3 sets of corneal measurements each
Subject repositioned between measurements
Inclusion criteria:
No prior intraocular and/or corneal surgery
No trauma, ocular or corneal diseases
No contact lens wear
20 eyes of 20 patients included
Gender: 6 males and 14 females
Age: 36±12.5 yrs (range 23 to 62 yrs)

5. Data analysis Repeatability Coefficient of variation (CV)
Standard deviation (SD)
Intraclass correlation coefficient (ICC)
Vector analysis for astigmatism measurements for each device

6. Data analysis Comparability
Comparison of corneal powers between devices
(average of corneal powers from 3 repeated measurements)
Analysis of variance (ANOVA)
Agreement in measurements between devices
Bland and Altman method
The 95% limits of agreement (95% LoA) calculated as mean difference ± 1.96 standard deviation (SD)
Interdevice correlation
Pearson correlation coefficient
Vector analysis of corneal astigmatism

7. Results- Repeatability of 3 measurements
0.18±0.12
0.09±0.07
0.22±0.12
0.12±0.07
CV (%) ± SD
Manual
IOLMaster
Atlas
Galilei
Device
0.077
0.042
0.096
0.055
SD (D)
0.996
0.994
0.998
ICC
There were no statistically significant differences among the devices (all P > 0.05), although there were trends for better repeatability for the IOLMaster and Galilei

8. Astigmatism: Vector differences between repeated measurements (% of eyes)
40 values for each device (20 for measurement 1-2 and 20 for measurement 1-3)
Difference between measurements
≤0.25D
≤0.50D
≤0.75D
≤1.00D
Galilei 40 83 98
100
Atlas 63 90
IOLMaster 73 95
Manual 55
The vector differences between repeated measurements were within 0.75 D except for Galilei and Atlas. Although Galilei tended to have smaller % of eyes within 0.25 D between repeated measurements, there were no significant differences among devices (Cochran’s Q test, all P>0.05).

9. Results – Comparability
Multiple comparison of measurements with each device
Differences between devices
Mean (D)
SD (D)
Min (D)
Max (D)
Galilei-Atlas
-0.08
0.14
-0.27
0.22
Galilei-IOLMaster *
-0.12
0.07
-0.22
0.06
Galilei-Manual
0.05
0.13
-0.19
0.40
Atlas-IOLMaster
-0.04
0.12
-0.31
0.17
Atlas-Manual *
-0.15
0.48
IOLMaster-Manual *
0.16
-0.02
0.44
*Significant difference between devices using ANOVA with Sidak adjustment (P<0.05) However, the highest mean difference was only 0.16 D, which is of minimal clinical importance

10. Interdevice correlation
y = x
R2=
40.00
41.00
42.00
43.00
44.00
45.00
46.00
47.00
Galilei SimK
IOLMaster K
Galilei SimK vs. IOLMaster
Pearson
coefficient (r)
Galilei-IOLMaster
0.9988
Galilei-Atlas
0.9954
Galilei-Manual
0.9959
Galilei SimK vs. Atlas K
y = x
R2=
40.00
41.00
42.00
43.00
44.00
45.00
46.00
47.00
Galilei SimK
Atlas K
Galilei SimK vs. Manual K
y = x
R2=
40.00
41.00
42.00
43.00
44.00
45.00
46.00
47.00
Galilei SimK
Manual K
The Pearson coefficients were higher than 0.99 between devices, indicating high
correlation

11. Interdevice correlation
y = x
R2=
40.00
41.00
42.00
43.00
44.00
45.00
46.00
47.00
Atlas K
IOLMaster K
Atlas K vs. IOLMaster
Pearson
coefficient (r)
Atlas-IOLMaster
0.9963
Atlas-Manual
0.9954
IOLMaster-Manual
0.9967
Atlas K vs. Manual K
40.00
41.00
42.00
43.00
44.00
45.00
46.00
47.00
Atlas K
Manual K
y = 0.984x
R2=
IOLMaster vs. Manual
y = x
R2=
40.00
41.00
42.00
43.00
44.00
45.00
46.00
47.00
IOLMaster K
Manual K
The Pearson coefficients were higher than 0.99 between devices, indicating high
correlation

12. Agreement in measurements between devices
-0.5
-0.3
-0.1
0.1
0.3
0.5 40 42 44 46
Mean corneal power (D) of the Atlas and manual keratometer
Difference in corneal power (D)
LoA=0.53
-0.5
-0.3
-0.1
0.1
0.3
0.5 40 42 44 46
Mean corneal power (D) of the Atlas and IOLMaster
Difference in corneal power (D)
LoA=0.48
-0.5
-0.3
-0.1
0.1
0.3
0.5 40 42 44 46
Mean corneal power (D) of the IOLMaster and manual keratometer
Difference in corneal power (D)
LoA=0.45
The range of the 95% LoA between devices was approximately 0.50 D.

13. Agreement in measurements between devices
-0.5
-0.3
-0.1
0.1
0.3
0.5 40 42 44 46
Mean corneal power (D) of the Galilei and IOLMaster
Difference in corneal power (D)
LoA=0.27*
-0.5
-0.3
-0.1
0.1
0.3
0.5 40 42 44 46
Mean corneal power (D) of the Galilei and Atlas
Difference in corneal power (D)
LoA=0.54
-0.5
-0.3
-0.1
0.1
0.3
0.5 40 42 44 46
Mean corneal power (D) of the Galilei and
manual keratometer
Difference in corneal power (D)
LoA=0.51
*The range of the 95% LoA between the Galilei and IOLMaster was significantly smaller than those for the other 5 paired comparison (see previous slide).
It was approximately 0.25 D less than the values for other 5 pairs of devices.

14. Mean astigmatism obtained from each device
Mean corneal astigmatism
Galilei
Atlas
IOLMaster
Manual keratometer
No significant differences among devices

15. Discussion
All devices demonstrated excellent reproducibility in measuring corneal powers
CV of 3 repeated measurements: lower than 0.22%
SD of 3 repeated measurements: range to 0.096D
ICCs: higher than 0.99
The differences in astigmatism between repeated measurements were within 0.75D for all devices, except for one pair of measurements each for the Galilei and Atlas

16. Discussion In our study, there were significant differences between
Galilei-IOLMaster, Atlas-Manual and IOLMaster-Manual
However, the highest mean difference was only 0.16D.
One factor contributing to these differences is the slightly different regions measured by each device
Measuring area
Galilei
1-4mm diameter
Atlas
Points at 3mm zone
Hexagonal pattern
at a diameter of around 2.4-mm
IOLMaster
Manual
Varies depending on corneal power

17. Conclusion
The corneal power measurements from these 4 devices were highly reproducible, comparable and correlated
Clinical studies are needed to refine how to best use these devices for astigmatic surgical planning and IOL calculations, particularly for complex cases (eg, post-LASIK)