Abstract
Purpose: :
As part of routine MRI examinations, oculodynamic MRI (od-MRI) movies offer a new fast (<30s) means to visualize eye movements in living patients. The objective of this pilot study is to improve visualization of orbital structures, in particular the extra ocular muscles (EOM), the eye and the ON.
Methods: :
A 1.5T od-MRI was obtained with a TrueFISP sequence (180ms/image, 1.3x1.3 mm spatial resolution) in a 28y old control subject and a 43y old female with bilateral high myopia (-20 dpt). Horizontal eye movements were assessed using a sagittal slice with a thickness of 5 mm. The information was computed and visualized, using special image processing procedures in combination with direct volume rendering.
Results: :
Od-MRI movies correlated well with the clinical findings. In the patient it showed a highly elongated eye bulb with a posterior staphyloma. On horizontal eye movement, the optic nerve of the myope curved more and abduction stopped at midline, where the posterior pole of the eye was constrained by orbital tissue, i.e. the medial rectus muscle and the periost. This correlated well with her esotropia of + 20° and her ocular motility which was impaired in all directions of gaze, in particular: abduction was only possible to midline. The improved visualization technique increased the borders of tissue contrast and thus facilitated identification of sclera, periost and muscle structures. In particular, in both subjects an orbital layer could be distinguished from a global layer in the both rectus muscles. Also, changes consistent with passive velocity induced movement of the vitreous were seen.
Conclusions: :
To our knowledge, this is the first report of an od-MRI imaging that allows visualization of movement of the vitreous and identification of the global and orbital EOM layers. It offers a potential clinical application to study differing functions of the global and orbital EOM.
Keywords: eye movements • imaging/image analysis: clinical • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)