[The posterior portion of the eyeball and the muscle cone in cases of high myopia].

PURPOSE

To study the displacement of the eyeball of high myopia in the muscle cone.

METHODS

Three patients with esotropia with high myopia(myopic esotropia group), seven patients with high myopia without esotropia (high myopia group), and eight controls(control group) were examined. Using magnetic resonance imaging, the outer axial length and the displacement of the posterior portion of the eyeball in the muscle cone were measured. In order to neglect individual differences, the coronal scanning was perpendicular to the orbital axis. The displacement was measured in the plane 2 mm and 4 mm anterior from the globeoptic nerve junction. The distance of the displacement was represented by the distance from the center of the globe to the center of the muscle cone.

RESULTS

The displacement in the plane 4 mm anterior (mean +/- standard deviation) was greater in the order of the myopic esotropia group(1.6 +/- 0.64 mm), the high myopia group(1.2 +/- 0.51 mm), and the control group(0.059 +/- 0.35 mm). The displacement of the eyeball was largest in the myopic esotropia group(p < 0.001). The outer axial length and the distance of the displacement in all cases was correlated significantly(r = 0.93, p < 0.01). Moreover, the eyeballs of the myopic esotropia group and the high myopia group were displaced upwards in the temporal area.

CONCLUSIONS

The posterior portion of high myopia was displaced upwards in the temporal area in the muscle cone regardless of the presence or absence of esotropia. The eyeball originally elongates upwards in the temporal area, not towards the weakest part of the muscle cone.