Quantification of optic nerve length and tortuosity in thyroid eye disease

Abstract

To objectively quantify the length and tortuosity of optic nerves (ONs) in patients with thyroid eye disease (TED), in relation to the occurrence of dysthyroid optic neuropathy (DON). All patients seen by 2 of the senior authors over a period of 12 years were screened for study entry. The primary outcome was the quantitative measurement of ON tortuosity and length in relation to the occurrence of DON. Image analysis involved the creation of a 3-dimensional reconstruction of the ON from the anterior clinoid process to the posterior globe using image analysis software. A centreline was created through the middle of the reconstruction, and the length of the ON was calculated as the length of this centreline. Tortuosity was calculated by creating a ratio between the straight-line length of the ON and the actual length (centreline length). The final sample included 50 patients who contributed 100 orbits, of which 26 orbits had DON. There were no differences in the Hertel exophthalmometry readings between patients with and without DON (p = 0.56). There was no significant relationship between the length (p = 0.39) and tortuosity (p = 0.82) of the ON and occurrence of DON. There is no significant relationship between the length and tortuosity of the ON and development of DON in patients with TED.