MRI measurements of orbital tissues in dysthyroid ophthalmopathy

Abstract

MRI technique makes it possible to observe and evaluate quantitatively the volume of all six extraocular muscles and the orbital fatty tissue in dysthyroid ophthalmopathy. It also makes it possible to evaluate changes in morphology during eye muscle contraction.

Eye muscle force development and saccadic velocity in thyroid-associated ophthalmopathy

“…Furthermore, since the steady-state tension was increased for movements in all directions of gaze, both vertically and horizontally, it would seem that the disease process affected all the external eye muscles, at least all the rectus muscles. This has also been shown in MRI studies of the patients, as reported previously [9]. Further evidence for a nonparetic origin of the eye movement disturbance in TAO is derived from correlations between saccadic velocity and tension development, which have been shown to be linear and not significantly different from those of normal muscle.…”

“…The inflammatory process can cause marked swelling of the extraocular muscles as demonstrated by imaging procedures such as computed tomography [4] and magnetic resonance imaging (MRI) [9]. The clinical characteristics of TAO include exophthalmos, disturbances of ocular motility and, in severe cases, reduction in vision due to optic neuropathy.…”

Significance of orbital fatty tissue for exophthalmos in thyroid-associated ophthalmopathy

“…In particular, the orbital fatty tissue can be more clearly distinguished from the other tissues using T1-weighted MRI because its signal intensity is much higher. However, there are only a few MRI orbital volume studies of both extraocular muscles and orbital fatty tissue [13,14,23]. In our previous studies [14,23] on orbital volume measurements, it was shown that the volume of the orbital fatty tissue was much greater than that of the extraocular muscles.…”

“…However, there are only a few MRI orbital volume studies of both extraocular muscles and orbital fatty tissue [13,14,23]. In our previous studies [14,23] on orbital volume measurements, it was shown that the volume of the orbital fatty tissue was much greater than that of the extraocular muscles. It is therefore possible that the increase in orbital fatty tissue volume in TAO is a more important cause of exophthalmos than the increase in extraocular muscle volume.…”

“…The details of measurements were described in our previous report [14,23]. The bony orbital cavity was traced along the orbital margin and the line between the zygomatic and lacrimal bones (Fig.…”