A study of the anatomical action of the lower eyelid retractors in Japanese

To clarify the morphological change in both the lower eyelid and the orbital fat beneath it associated with eyeball rotation, tests were performed on 11 living subjects by MRI (magnetic resonance imaging) and on 26 dissected cadavers. The MRI study: during downward gazing, in 9 cases out of 11, the inferior oblique muscle was recorded (ie. the lower eyelid contorted and retracted along the perimeter of the eyeball and its fat was moved into the orbital cavity). In the other 2 cases, the aforementioned contortion and retraction did not occur and the eyelid fat remained outside the orbital cavity. In the para-sagittal section along the optic nerve, the area of herniating fat was significantly less when the eyeball rotated downwards than when it gazed upwards. The anatomical study: in all cases, connectiong fibers originating in both Tenon's capsules around the muscles and from the lower eyelid retractors reached the capsule of orbital fat. In cases where there was plentiful orbital fat, the subjects had numerous connective fibers, The connective fibers may support the fat and help to retract it posteriorly. This would cause the recession of the lower eyelid retractors during contraction of the inferior rectus muscle, i.e. when looking downwards.