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Thomas H. Krzizok, Bernd U. Schroeder; Measurement of Recti Eye Muscle Paths by Magnetic Resonance Imaging in Highly Myopic and Normal Subjects. Invest. Ophthalmol. Vis. Sci. 1999;40(11):2554-2560.
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purpose. To analyze the path of extraocular muscles (EOMs) quantitatively in
highly myopic subjects with and without restricted eye motility versus
control. To elucidate the cause of the acquired motility disorder in
patients with high myopia.
methods. Thirty-three orbits were imaged using a Magnetom or Siemens Vision
(Siemens, Erlangen, Germany; both 1.5 Tesla) MRI (magnetic resonance
imaging) scanner. Coronal T1-weighted, spin-echo images
were obtained with repetition time of 550 msec and echo time of 15
msec. Subjects had to fixate in different positions of gaze. Orbits of
three 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); control group (n= 11), emmetropic subjects with normal eye motility (average
axial length, 23.6 mm).
results. Highly myopic patients showed significant displacements of recti EOMs
in comparison with control subjects. Mean displacements, 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 and in group 2, LR 1.4 mm
(1.3 downward, 0.6 medial) and MR 1.2 mm downward. In groups 1 and 2
the inferior rectus (IR) was displaced 1.3 mm medially and upward. In
both groups of myopic patients the superior rectus (SR) was displaced
1.5 mm medially and downward.
conclusions. In patients with high axial myopia, displacements of all recti EOMs can
be detected by MRI. Displacements of SR, MR, and IR were very similar
in groups 1 and 2 versus control. LR displacement into the lateral and
inferior quadrant of the orbit was greatest in patients with restricted
eye motility. Thus, LR displacement is probably the 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.
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