Elucidation of restrictive motility in high myopia by magnetic resonance imaging.

OBJECTIVE To elucidate the cause of an acquired, restrictive motility disorder in patients with high myopia. METHODS Magnetic resonance imaging (MRI) scans were obtained from 37 patients with high myopia (axial length of globe, 29.4 mm; refractive error, > -15 diopters). Additional dynamic MRI scans were obtained in which the patient fixated in various positions with the less restricted eye for 50 seconds. Twenty normal orbits were studied in control MRI scans. RESULTS The path of the lateral rectus, in the anterior and midorbital regions, was displaced downward an average of 3.4 mm in 13 patients with typical esotropia and hypotropia. This mislocation reduces abducting torque of the lateral rectus and creates depressing and extorting moments. The muscle insertions were normal, except where previous strabismus surgery relocated them. Contact between the enlarged globe and the bones of the orbital apices that would cause esotropia was not observed. CONCLUSIONS This eye muscle abnormality in patients with high myopia is another strabismus syndrome related to abnormalities of orbital connective tissues and muscle paths. Orbital MRI scans may be useful before strabismus surgery in patients with high myopia. If an abnormal lateral rectus path is found, surgery should be directed to normalize it. Magnetic resonance imaging morphometry in high myopia may give additional information on orbital anatomy and biomechanical mechanisms of strabismus.