Orbital CT Imaging for Proptosis Measurement

All patients were scanned with a 256-slice MDCT scanner (Brilliance 256; Philips Medical Systems, OH, USA), as previously described^{19 (link)}. Orbital CT scans were obtained using contiguous axial slices, with the patient’s head positioned parallel to the Frankfurt plane. Patients were asked to look at a fixed point, and the scanning parameters were as follows: 120 kV, 150 mAs, 64 × 0.625 mm detector configuration, 1 mm slice thickness, and 1 mm slice increment. Measurement of proptosis was performed on the CT image by drawing a horizontal line between the lateral orbital rims on an axial plane that bisects the lens and then drawing a perpendicular line forward to the posterior surface of the cornea^{18 (link)}. The posterior surface of the cornea was chosen because it can be difficult to define the anterior surface of the cornea on CT.