FA and mean diffusivity levels measured with the diffusion tensor imaging of the thyroid orbitopathy patients were affected. The changes in diffusion tensor imaging were also correlated with the ophthalmologic tests of the patients.
We really appreciate Lee et al.'s comments regarding our recently published study on diffusion tensor imaging in patients with Graves' Ophthalmopathy (GO). They indicated that an explanation for the increased mean fractional anisotropy (FA) values and decreased mean diffusivity values of the intraorbital optic nerve in patients with thyroid ophthalmopathy was needed. However, our study showed that the mean FA was decreased and the mean diffusivity was increased in patients with GO as they have mentioned before. We have cited Engelhorn at al.'s study that found a good correlation between an increase in radial diffusivity, as well as a decrease in FA measured in the intracranial part of the optic nerve and in the optic radiation. 1 Engelhorn et al. found that these changes were correlated with the optic nerve atrophy and spatial temporal contrast sensitivity of the retina. This study shows that the optic nerve damage could be detected with diffusion tensor imaging.Lee et al. commented about the reason for evaluating the intraorbital part of the optic nerve in our study. GO is a disease of the orbit, which is characterized by edema, and inflammation of extraocular muscles and an increase in orbital connective tissue and fat. The compression of the optic nerve often results with the optic neuropathy in patients with GO. For this reason, we planned to evaluate the intraorbital part of the optic nerve. There are other studies that show diffusion tensor imaging (DTI) changes of the intraorbital part of the optic nerve in diseases, such as traumatic optic neuropathy and optic neuritis. 2,3 As they have pointed out, we ignored the movement of the optic nerve in our study. Engelhorn et al. 1 reported that they did not evaluate the intraorbital part of the optic nerve to avoid movement artifacts. But even different locations of the intraorbital part of the optic nerve can be evaluated with DTI. 4 As we mentioned before, there are other studies that evaluate the intraorbital part of the optic nerve. [2][3][4] In addition, we compared our results with healthy control subjects and there was a significant difference between the groups. However, using a fixation point might enhance the measurements.Early optic nerve dysfunction can be detected with visual field examination. For this reason, we planned to correlate 4 quadrants of the optic nerve with visual field examinations of the patients. The diameter of the intraorbital segment of the
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