Comparability of proptosis measurements by different techniques

Abstract

Purpose: To compare measurements of proptosis obtained by clinicians and computed tomography.

Design: Cohort study.

Methods: In a prospective randomized study of orbital radiotherapy for Graves' ophthalmopathy, measurements of proptosis were made on the same visit by an endocrinologist and an ophthalmologist using the Krahn exophthalmometer and by a technician using orbital computed tomography (CT) scans taken with head fixation to minimize position artifact.

Results: Both clinical observers recorded proptosis measurements that were greater by 0.6 to 1.6 mm than those observed on the CT scan. This discrepancy resulted in part from the clinical measurements being made to the anterior corneal surface, whereas the CT measurements were made to the posterior corneal surface (a difference of approximately 0.5 mm). The aggregated observations of the clinicians did not vary significantly from each other but wide discrepancies (as much as 5 mm) were noted between single measurements made on the same patient and on the same day by different clinicians.

Conclusions: The degree of variance observed in clinical measurements emphasizes the importance of defining reproducibility of the measurement techniques in prospective studies of therapeutic efficacy in patients with Graves' ophthalmopathy. The systematic difference between CT and clinical measurements of proptosis should be noted when results of clinical trials are compared.