1. Comparison of Central Corneal Thickness, Anterior Chamber Depth, and Central Corneal Power Measurements between Two Scheimpflug Imaging Systems Yuichi Hori, MD, PhD, and Yuzo Deguchi, MD Department of Ophthalmology Toho University Sakura Medical Center, Sakura, Japan Financial disclosure: The authors have no financial interest in any aspect of this presentation.

2. Background Measurements of corneal thickness and curvature are of paramount importance in corneal refractive surgery. A rotating Scheimpflug analysis system allows acquisition of multiple images of the anterior segment of the eye and calculation of measurements of the central corneal thickness (CCT), corneal curvature, and anterior chamber depth (ACD). Several rotating Scheimpflug analysis systems are available for use in the clinic.

3. Purpose To compare the preoperative CCT, ACD, and central corneal power measured with the Pentacam HR™ (Oculus Optikgeräte GmbH, Germany) rotating single Scheimpflug camera and the Galilei™ Dual Scheimpflug Analyzer (Ophthalmic Systems AG, Switzerland) in normal corneas.

4. Subjects 43 right eyes of 43 patients (21 women, 22 men) scheduled to undergo cataract surgery at the Department of Ophthalmology, Toho University Sakura Medical Center Mean age: 60.8 ± 16.5 years No corneal abnormalities as verified by slit-lamp examination Mean spherical equivalent: -1.24 ± 2.05 diopters (D)

5. Methods Each patient underwent imaging with both rotating Scheimpflug imaging systems, the Pentacam HR and the Galilei The instruments were used in random order. The CCT, ACD, and central corneal power (front and back axial powers) were compared between the two Scheimpflug imaging systems. The data obtained with the two modalities were presented graphically on Bland-Altman plots. Pentacam HR™Galilei™

6. CCT Mean (-14.11) Mean - 2 SD Mean +2 SD Average CCT (um) CCT Pentacam – CCT Galilei (um) Mean-14.11 SD12.86 2 SD25.72 Bland-Altman plot Pentacam HR (um)Galilei (um) Mean 542.6556.0 Standard Deviation (SD) 33.632.7 * P < 0.001, paired t test Results 1 The mean CCT values measured with the Pentacam HR (mean, 542.4±33.6 um) was significantly (p<0.001, paired t test) thinner than that measured with the Galilei (556.0±32.7 um). CCT Pentacam – CCT Galilei (um)

7. ACD Average ACD (mm) ACD Pentacam – ACD Galilei (mm) Mean-0.018 SD0.0625 2 SD0.1250 Bland-Altman plot Pentacam HR (mm)Galilei (mm) Mean 2.83 SD 0.530.47 * P = 0.24, paired t test Results 2 There was no significant (p=0.24) difference between the ACD measurements obtained using the Pentacam HR (2.83±0.53 mm) and the Galilei (2.83±0.47 mm). Mean +2 SD Mean -2 SD Mean (-0.018) ACD Pentacam – ACD Galilei (mm)

8. Central Corneal Power (front axial power) Average front central axial power (D) Front axial power: Pentacam –Galilei (D) Mean0.121 SD0.518 2 SD1.035 Bland-Altman plot Pentacam HR (D)Galilei (D) Mean 44.5844.46 SD 1.091.13 * P = 0.133, paired t test Results 3 There was no significant (p=0.133) difference between the central corneal power (front axial power) measurements obtained using the Pentacam HR (44.58±1.09 D) and the Galilei (44.46±1.13 D). Mean +2 SD Mean -2 SD Mean (0.121) Front central axial power: Pentacam –Galilei (D)

9. Central Corneal Power (back axial power) Average back central axial power (D) Back axial power: Pentacam –Galilei (D) Mean0.2 SD0.163 2 SD0.327 Bland-Altman plot Pentacam HR (D)Galilei (D) Mean -6.38-6.58 SD 0.230.24 * P < 0.001, paired t test Results 4 The mean back central axial power measured by the Galilei (-6.58±0.24 D) was significantly (p<0.001) smaller than that measured by the Pentacam HR (-6.38±0.23 D). Mean +2 SD Mean -2 SD Mean (0.2) Back central axial power: Pentacam –Galilei (D)

10. Summary The CCT measured with the Pentacam HR was significantly thinner (approximately 14 um) than that measured with the Galilei. There was no significant difference between the ACD measurements obtained with the two imaging systems. There was no significant difference between the front central axial power measured by the two systems. However, the back central axial power measured by the Galilei was significantly smaller (approximately 0.2 diopter) than that measured by the Pentacam HR.

11. Discussion/Conclusion The Galilei is designed to analyze the anterior ocular segment using dual rotating Scheimpflug cameras integrated with a Placido topographer. This design may lead to differences in measurements between the Pentacam HR and the Galilei. We should know the characteristics of the data measured with these systems.

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