Quantification of recti eye muscle paths in high myopia

To elucidate the etiology of an acquired, restrictive motility disorder in patients with high myopia.

Thirty-three orbits were imaged using a Siemens Magnetom or Siemens Vision (both 1.5 Tesla) MRI (magnetic resonance imaging) scanner, applying a head coil. Coronal T1-weighted, spin-echo images were obtained. Orbits of three different patient groups were analyzed. Group 1 (n = 14): patients with high axial myopia and restricted eye motility (average axial length = 31.4 mm; refractive error more than -15 D). Group 2 (n = 8): subjects with high axial myopia and normal eye motility (average axial length = 29.2 mm). Controls (n = 11): emmetropic subjects with normal eye motility.

Highly myopic patients showed significant displacements of recti EOMs in comparison to the controls. Mean displacements as measured in the plane 3 mm anterior to the globe-optic nerve junction in primary gaze were, in group 1: lateral rectus (LR) 2.9 mm (2.5 downward, 1.4 medial), medial rectus (MR) 1.3 mm downward. In group 2: LR 1.4 mm (1.3 downward, 0.6 medial) and MR 1.2 mm downward. In both groups 1 and 2, the inferior rectus (IR) was displaced 1.3 mm medially and upwards. In both groups of myopic patients the superior rectus (SR) was displaced 1.5 mm medially and downwards.

In patients with high axial myopia, displacements of all recti EOMs can be detected by MRI. However, displacement of the LR into the lateral and inferior quadrant of the orbit is significantly greatest. We therefore assume LR displacement to be a major pathophysiological factor for the restrictive motility disorder in high myopia. EOM dislocations can be explained by myopia-associated alterations in the orbital connective tissues confining EOM positions in relation to the orbital wall.