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

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

Methods Prospective study Corneal power measurements by 4 methods All 4 devices use a refractive index of 1.3375 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)

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)

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

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

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

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).

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

Interdevice correlation y = 0.9943x + 0.3688 R2= 0.9977 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 = 0.9897x + 0.5303 R2= 0.9908 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 = 0.9789x + 0.8792 R2= 0.9918 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

Interdevice correlation y = 0.9974x + 0.1537 R2= 0.9925 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 + 0.5762 R2= 0.9908 IOLMaster vs. Manual y = 0.9842x + 0.5307 R2= 0.9934 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

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.

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.

Mean astigmatism obtained from each device Mean corneal astigmatism Galilei 0.54D @84 Atlas 0.51D @88 IOLMaster 0.62D @88 Manual keratometer 0.52D @87 No significant differences among devices

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 0.042 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

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

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)