Quantitative magnetic resonance morphometry of extraocular muscles: a new diagnostic tool in paralytic strabismus.

Paralytic strabismus is often diagnostically ambiguous due to the similarity of patterns of misalignment produced by different mechanisms. To address this problem, we have developed a new technique employing high-resolution, surface coil magnetic resonance imaging to quantify extraocular muscle size and contractility. Adjacent coronal images are obtained spanning the anteroposterior extent of each orbit, and repeated in multiple directions of gaze. Contractility is evaluated from analysis of muscle cross-sectional areas. The quantitative size and contractile characteristics of normal rectus and superior oblique muscles are reviewed, along with the effects of superior oblique palsy. The morphometric features of lateral rectus palsy are illustrated by three clinical cases exhibiting deficient contractility and atrophy of the lateral rectus muscle. A case of superior oblique palsy is presented illustrating atrophy and lack of contractility of the involved superior oblique muscle. This imaging technique can be employed in any clinical center and permits insight into extraocular muscle function in complex strabismus cases.