Axial Globe Position Measurement

Abstract

Purpose Identify a reproducible measure of axial globe position (AGP) for multicenter studies of patients with thyroid eye disease (TED). Methods This is a prospective, international, multicenter, observational study in which 3 types of AGP evaluation were examined: radiologic, clinical, and photographic. In this study, computed tomography (CT) was the modality to which all other methods were compared. CT AGP was measured from an orthogonal line between the anterior lateral orbital rims to the cornea. All CT measurements were made at a single institution by 3 individual clinicians. Clinical evaluation was performed with exophthalmometry. Three clinicians from each clinical site assessed AGP with 3 different exophthalmometers and horizontal palpebral width using a ruler. Each physician made 3 separate measurements with each type of exophthalmometer, not in succession. All photographic measurements were made at a single institution. AGP was measured from lateral photographs in which a standard marker was placed at the anterior lateral orbital rim. Horizontal and vertical palpebral fissure were measured from frontal photographs. Three trained readers measured 3 separate times, not in succession. Exophthalmometry and photography method validity was assessed by agreement with CT (mean differences calculation, ICC’s, Bland-Altman figures). Correlation between palpebral fissure and CT AGP was assessed with Pearson correlation. Intraclinician and interclinician reliability was evaluated using intraclass correlation coefficients (ICC). Results Sixty-eight patients from 7 centers participated. CT mean AGP was 21.37mm (15.96 – 28.90mm) right, 21.22mm (15.87 – 28.70mm) left (ICC 0.996 and 0.995). Exophthalmometry AGP fell between 18mm and 25mm. Intraclinician agreement across exophthalmometers was ideal (ICC 0.948 – 0.983). Agreement between clinicians was greater than 0.85 for all upright exophthalmometry measurements. Photographic mean AGP was 20.47mm (10.92 – 30.88mm) right, 20.30mm (8.61 – 28.72mm) left. Intrareader and interreader agreement was ideal (ICC 0.991 – 0.989). All exophthalmometers’ mean differences from CT ranged between −0.06mm (+/− 1.36mm) and 0.54mm (+/− 1.61mm); 95% CI fell within 1mm. Magnitude of AGP did not affect exophthalmometry validity. Oculus best estimated CT AGP but differences form other exophthalmometers were not clinically meaningful in upright measurements. Photographic AGP (right ICC=0.575, left ICC=0.355) and palpebral fissure do not agree with CT. Conclusions Upright clinical exophthalmometry accurately estimates CT AGP in TED. AGP measurement was reliably reproduced by the same clinician and between clinicians at multiple institutions using the protocol in this study. These findings allow reliable measurement of AGP that will be of considerable value in future outcome studies.

A Comparative Study of Clinical vs. Digital Exophthalmometry Measurement Methods

“…CT also correlated well with HE. Both observations are compatible with those of previous studies [6][7][8]16].…”

“…In addition, accuracy remained unchanged as the degree of proptosis increased. Previous studies have yielded inconsistent results in this regard: some have found accuracy to be negatively associated with the degree of proptosis [2,17], while others have not [8]. e high levels of reliability and reproducibility observed in this study (ICC � 0.93 for clinical measurements; ICC � 0.95 for radiological measurements) match the results of several other studies [3,4,16].…”

“…After acquisition, images were processed and analyzed with the dedicated workstation software (Extended Brilliance Workspace (EBW) Philips Medical Imaging, Best, the Netherlands) e images were examined by a head-andneck radiologist and by a second reader, both of whom were blinded to the clinical condition of the patient. Having selected the full-orbit image with the greatest intraocular lens thickness, a line was drawn from the zygomatic rhymes to the anterior surface of the cornea in order to measure exophthalmos (Figure 1(c)) [8,11]. e images of the right and left orbits were evaluated independently.…”

“…As shown by several authors, computed tomography (CT) correlates well with HE while providing greater accuracy, [5][6][7][8] but the high cost, exposure to radiation, and the need for repeated measurements severely restrict the use of this technology for routine exophthalmometry.…”

“…e authors found the correlation between the methods to be weak, possibly due to the fact that the study was multicentric and involved different photographers and evaluators, compromising reliability and reproducibility [8].…”