Quantitative assessment of the intraorbital segment of the optic nerve in patients with thyroid orbitopathy using diffusion tensor imaging

Background It is difficult to detect optic nerve changes in patients with thyroid-associated ophthalmopathy (TAO) before the development of optic neuropathy. Purpose To detect changes in the intraorbital segment of the optic nerve in patients with TAO using diffusion tensor imaging (DTI) and determine any correlations with disease severity. Material and Methods A total of 74 participants (17 normal, 22 mild, and 35 moderate-severe TAO) were organized to be given 3-T DTI to measure fractional anisotropy (FA) and mean diffusivity (MD) for the orbital segments of their optic nerves. All underwent ophthalmological examinations for visual acuity, intraocular pressure, exophthalmos, and fundoscopy, and were assessed based on the Clinical Activity Score (CAS). Univariate analysis of variance and Pearson's correlation coefficients were carried out. Results Patients with moderate-to-severe TAO had significantly lower FA values and higher MD values (P < 0.05). FA values were negatively correlated with CAS but had no obvious correlations with the degree of exophthalmos. MD values had no obvious correlations with CAS or the degree of exophthalmos. Conclusion DTI parameters of the intraorbital optic nerves were significantly altered in moderate-to-severe patients before onset of clinical optic nerve dysfunction and may, therefore, be used as an imaging biomarker for assessing the disease.