Search

Purpose To determine the incidence of divided bellies of the inferior oblique (IO) muscle in embalmed and fresh cadavers, and to elucidate the symmetry of IOs in the left and right eyes. Design Cohort study. Methods IOs were dissected from their origin to the insertion point in 40 intact orbits of 20 embalmed cadavers and in 22 intact orbits of 11 fresh cadavers. The width and location of the IO origin were measured in the skull. In addition, the locations and patterns of IO insertions on the globe were recorded. Results Divided bellies were evident in 18 of the 40 IOs (45%) in the 20 embalmed cadavers but in none of the 22 IOs in the 11 fresh cadavers. The insertional patterns of the IOs differed between the left and right eyes in 12 of 31 cadavers (39%). Conclusions Dehiscence attributable to the loss of intermuscular fatty tissue and shrinkage in the postmortem state could be mistaken for actual divided bellies in embalmed cadavers. Future studies should investigate the incidence of multiple insertions of IOs in a large number of fresh cadavers. In addition, ocular surgeons should be aware of the possibility of differences in the insertional anatomy of IOs between the left and right eyes.

Purpose To investigate the superior oblique (SO) extraocular muscle cross section in normal controls and in SO palsy using high-resolution magnetic resonance imaging (MRI). Design Prospective observational study. Methods At a single academic medical center, high-resolution MRI was obtained at 312 μm in-plane resolution using surface coils in multiple, contiguous, quasi-coronal planes perpendicular to the orbital axis in 12 controls and 62 subjects with SO palsy. Previous strabismus surgery was excluded. Imaging was repeated in central gaze and infraduction. In each image plane along the SO, its cross section was outlined to compute cross-sectional area and the major and minor axes of the best-fitting ellipse. Main outcome measures were SO morphology and ocular motility. Results The major and minor axes, cross-sectional area distributions, and volume of the SO belly were subnormal in orbits with SO palsy at most anteroposterior locations ( P = .001), but discriminant analysis showed that palsied SO cross sections segregated distinctly into round and elongate shapes representing isotropic vs anisotropic atrophy, respectively. The major axis was relatively preserved in anisotropic atrophy ( P = .0146). Cases with isotropic atrophy exhibited greater hypertropia in infraversion than central gaze, as well as greater excyclotorsion, than cases with anisotropic atrophy ( P Conclusions Characteristic differences in shape of the palsied SO belly correlate with different clinical features, and may reflect both the degree of differential pathology in the medial vs lateral neuromuscular SO compartments and the basis for diversity in patterns of resulting hypertropia.