APPENDIX
Figure A1. Validation of the image composition procedure
To validate the repeatability and the reproducibility, images from 12 healthy volunteers were tested. Reference points (A-C, white dots) were marked on each image as follows: A, the point on the anterior corneal surface which was lying on the Axis line in the central horizontal image; B, the farthest scleral surface point from the rotation axis in the nasal image; C, the farthest scleral surface point from the rotation axis in the temporal image (top). The
reviewers composed the best matched image by rotation and movement of nasal and temporal images using Microsoft PowerPoint version 2007 and determined the x, y coordinates of A (X1, Y1), B’ (X2, Y2; corresponding point to B) and C’ (X3, Y3;
corresponding point to C) using Image J software version 1.44d (bottom). The reviewers were blinded to the results of other reviewers.
The absolute difference values between the x, y coordinates of A and B’ (X2-X1 and Y1-Y2) or A and C’ (X1-X3 and Y1-Y3) were calculated. Each value was converted to the metric unit (mm) by dividing it by reference pixels corresponding to 1.00 mm. Pearson’s correlation coefficient and intraclass correlation coefficient (ICC) were used to assess intra- and inter- observer reliability. The absolute difference values in the x, y coordinates between A and the points used in actual analyses (NL, N1, N2, N3, TL, T1, T2, and T3 in Fig.1) are thought to be much smaller than those between A and B’ or A and C’ because B and C are the anterior surface points which travel the longest distance on image rotation.
Images from 12 healthy volunteers were used to validate the image composition procedure.
Calculations of Xn, Yn, Xt and Yt showed an excellent level of intra- and inter-observer agreement.
Table A1. Reliability of the image composition procedure.
First measurement
(mm)
Second measurement
(mm)
Absolute difference
(mm)
Pearson’s Correlation Coefficient
Intraclass Correlation Coefficient
r P ICC P
Intraobserver reliability
Xn 13.35 ± 0.60 13.33 ± 0.60 0.17 ± 0.14 0.927 <0.001 0.927 <0.001 Yn 9.48 ± 0.94 9.50 ± 1.08 0.17 ± 0.11 0.989 <0.001 0.979 <0.001 Xt 12.17 ± 0.51 12.28 ± 0.41 0.19 ± 0.14 0.920 <0.001 0.899 <0.001 Yt 10.54 ± 1.24 10.68 ± 1.15 0.28 ± 0.13 0.975 <0.001 0.972 <0.001 Interobserver reliability
Xn 13.35 ± 0.60 13.27 ± 0.67 0.17 ± 0.12 0.958 <0.001 0.953 <0.001 Yn 9.48 ± 0.94 9.48 ± 1.08 0.17 ± 0.14 0.985 <0.001 0.976 <0.001 Xt 12.17 ± 0.51 12.19 ± 0.41 0.21 ± 0.16 0.850 <0.001 0.833 <0.001 Yt 10.54 ± 1.24 10.59 ± 1.27 0.19 ± 0.10 0.986 <0.001 0.985 <0.001
Xn, the absolute difference value between the x coordinates of A and B’ (X2-X1); Yn, the absolute difference value between the y coordinates of A and B’ (Y1-Y2); Xt, the absolute difference value between the x coordinates of A and C’ (X1-X3); Yt, the absolute difference value between the y coordinates of A and C’ (Y1-Y3); ICC, Intraclass Correlation Coefficient.
