0. Comparative study of cornea and anterior segment biometric features between scanning slit beam technology, Placido disk topography, and a Scheimpflug imaging system
Juan Carlos Serna-Ojeda MD, Arturo Ramirez-Miranda MD, Alejandro Navas MD, MSc, Aida Jimenez-Corona MD, PhD and Enrique O. Graue-Hernandez MD, MSc
Department of Cornea and Refractive Surgery
Instituto de Oftalmologia “Conde de Valenciana”, Mexico City, Mexico
JCS-O, AJ-C and EOG-H have no financial interests to disclose. AR-M is a consultant for Carl Zeiss Meditec. AN is a consultant for Carl Zeiss Meditec and speaker for Alcon Laboratories and STAAR Surgical.

1. Purpose
We studied the interdevice agreement of three systems in the different measurements of the corneal and anterior segment biometric parameters.
The Pentacam HR ® (Oculus, Wetzlar, Germany).
The Orbscan ® (Bausch & Lomb, New York, USA).
The Aladdin ® (Topcon, Tokyo, Japan).

2. Methods
Randomly selected individuals aged 18 years or older were prospectively recruited from the general consultation from a Department of Cornea and Refractive Surgery.
Patients with previous ocular surgery, dry eye and use of contact lens in the previous month were excluded.
All eyes were examined undilated with the three devices.
Only high-quality measurements were included.

3. Methods Cornea and anterior segment biometric features:
Anterior corneal radius of curvature at 3 and 7 mm (Sim-Kmin and Sim-Kmax)
Anterior chamber depth (ACD)
White-to-white

4. Statistical analysis Interdevice intraclass correlation coefficient.
Interdevice agreement was assessed by the Bland–Altman comparison analysis.
95% limits of agreement (LoA) as mean difference ± 2 standard deviations of the differences.
Data were processed and analyzed using Microsoft Excel 2011© and SPSS version 17 (IBM Corp., NY)

5. Results Thirty-four eyes of 17 patients.
Median and Interquartile Range for the Measurements of Each Examined Variable
PARAMETER
Aladdin
Orbscan
Pentacam HR
Sim-Kmin (D)
42.80 (41.40 to 43.60)
42.3 (41.32 to 43.37)
42.40 (41.15 to 43.37)
Sim-Kmax (D)
45.11 (43.75 to 45.96)
44.8 (43.75 to 46.37)
44.95 (43.55 to 45.87)
ACD (mm)
3.76 (3.47 to 3.83)
3.01 (2.79 to 3.20)
3.14 (2.98 to 3.32)
White-to-white (mm)
11.74 (11.46 to 12.05)
11.65 (11.42 to 11.90)
Sim-K = simulated keratometry values; D = diopters; ACD = anterior chamber depth
Thirty-four eyes of 17 patients.
Nine subjects (52.9%) were female and eight (47.1%) were male.
Median age of 26 years (range 21 – 50 years).
15 candidates for refractive surgery, 1 suspect for keratoconus and 1 with keratoconus diagnosis.

6. 95% LoA (mean difference, P value)
Interdevice intraclass correlation coefficient and interdevice agreement analysis of the three systems.
Parameter
Aladdin - Orbscan
Aladdin - Pentacam HR
SimK-min (D) 
ICC
(95%CI)
0.937
(0.885 to 0.968)
0.968
(0.940 to 0.984)
95% LoA (mean difference, P value)
to 1.408
(0.321, p=0.898)
to 1.008
(0.206, p=0.851)
SimK-max (D)
0.983
(0.969 to 0.991)
0.976
(0.955 to 0.988)
1.119 to 1.287
(0.084, p= 0.566)
1.193 to 1.503
(0.155, p>0.01)
SimK = simulated keratometry; D = diopters; ICC = intraclass correlation coefficient; CI = confidence interval; LoA = limits of agreement.
ICC>0.9
P≤0.05

7. 95% LoA (mean difference, P value)
Interdevice intraclass correlation coefficient and interdevice agreement analysis of the three systems.
Parameter
Aladdin - Orbscan
Aladdin - Pentacam HR
ACD (mm)
ICC
(95%CI)
0.930
(0.872 to 0.965)
0.888
(0.801 to 0.944)
95% LoA (mean difference, P value)
0.458 to 0.908
(0.683, p=0.237)
0.285 to 0.834
(0.560, p=0.05)
White-to-white (mm)
0.727
(0.550 to 0.860)
to 0.517
(-0.064, p=0.921)
ACD = anterior chamber depth; ICC = intraclass correlation coefficient; CI = confidence interval; LoA = limits of agreement
ICC>0.9
P≥0.05

8. Aladdin vs Orbscan 95% LoA -0.767 to 1.408 p=0.898
K-min
Aladdin vs Pentacam
95% LoA to p=0.851
Aladdin vs Orbscan 95% LoA to p=0.898

9. Aladdin vs Orbscan 95% LoA -1.119 to 1.287 p=0.566
K-max
Aladdin vs Pentacam
95% LoA to 1.503
p>0.01
Aladdin vs Orbscan 95% LoA to p=0.566

10. Aladdin vs Orbscan 95% LoA 0.458 to 0.908 p=0.237
ACD
Aladdin vs Pentacam
95% LoA to 0.834
p=0.05
Aladdin vs Orbscan 95% LoA to p=0.237

11. Aladdin vs Orbscan 95% LoA -0.645 to 0.517 p=0.921
W-to-W
Aladdin vs Orbscan 95% LoA to p=0.921

12. Conclusions
All the analyzed parameters show a good to excellent Interdevice intraclass correlation coefficient.
Interdevice agreement is higher between Orbscan and Aladdin.
Orbscan and Pentacam may be used interchangeably with the Aladdin when analyzing Sim-Kmin and white-to-white.
ACD and Sim-Kmax should be carefully analyzed.