Computed Tomography Measurements as a Standard of Exophthalmos? Two-Dimensional Versus Three-Dimensional Techniques.

PURPOSE: To compare measurements of exophthalmos using two-dimensional (2D) and three-dimensional (3D) computed tomography (CT) methods.

METHODS: The CT data of 50 patients with thyroid eye disease were collected. The exophthalmos measurements were performed using both 2D and 3D methods. The protrusion of the globe center, the deviation angle of the ocular axis, and the distance between the globe center and the corneal apex were also recorded. The agreements between Hertel exophthalmometry and different CT measurements were analyzed, and the geometrical relationship between the protrusion of the corneal apex and globe center were analyzed.

RESULTS: The measurement agreement from consecutive CT scans was significantly better using the 3D method than the 2D method (p < 0.05). The difference in exophthalmos measurements between the 2D and 3D methods was 0.9 ± 1.2 mm (p < 0.05), and the 3D exophthalmos measurement was more consistent with Hertel exophthalmometry. The exophthalmos of the corneal apex and the globe center agreed with the geometrical formula well. The location error between the corneal apexes marked on the 2D and 3D images was correlated with the vertical deviation angle of the ocular axis (r = 0.516).

CONCLUSION: The reliability of CT measurements performed using a 3D method was better than those obtained using a conventional 2D method. The 3D measurements were also more consistent with the exophthalmometry results. The exophthalmos of the globe center might be considered an important reference for patients with severe strabismus.