Location and Gaze-Dependent Shift of Inferior Oblique Muscle Position: Anatomic Contributors to Vertical Strabismus Following Lower Lid Blepharoplasty?

[PURPOSE] This study investigated, using high-resolution magnetic resonance imaging (MRI), inferior oblique muscle (IO) position relative to the adnexa in normal controls, subjects with and without vertical strabismus following lower lid blepharoplasty, and subjects with other hypertropia.

[METHODS] Sagittal plane MRI was obtained in central gaze, infraduction, and supraduction in 19 controls, 11 subjects with and 2 without hypertropia following bilateral lower lid blepharoplasty, and 13 subjects with hypertropia unrelated to blepharoplasty. In the plane passing through the center of the inferior rectus muscle (IR), we analyzed IO position relative to the globe, as well as the distance from IO to the skin or orbital floor.

[RESULTS] The IO was located approximately 1 mm more anteriorly and 1.2 mm more inferiorly in hypertropic than hypotropic fellow orbits of the blepharoplasty group and controls (P < 0.05). From central gaze to infraduction, IO shift in subjects with blepharoplasty was redirected inferiorly, rather than posteriorly as in all other groups. However, from central gaze to supraduction, IO motion was similar in all groups. There was scarring between the IO-IR pulley and orbital floor in the hypertropic eye after lower lid blepharoplasty.

[CONCLUSIONS] Subjects with strabismus following lower lid blepharoplasty exhibit anterior and inferior IO pulley displacement in central gaze, as well as hindrance to normal posterior shift in infraduction. Proximity of IO to the orbital rim and lower eyelid skin is associated with strabismus following blepharoplasty, possibly because lower lid blepharoplasty may change lid forces on the IO-IR pulley system via scar tissue.