Study of the inferior oblique muscle of the eye by MRI

The utility of the inferior oblique m. radioanatomical study by a FLASH 3D sequence in magnetic resonance imaging (MRI). Twenty eyes (ten healthy volunteers aged 21–32 years, without any history of significant ocular pathology) were explored by MRI (1 Tesla; cranial coil) and comparisons were made between spin echo (SE) T1 sequence (through the neuro-ocular and coronal planes; thickness of slices = 3 mm) and a gradient echo FLASH 3D sequence (thickness of slices = 1 mm). This enabled a mm by mm reformation of the inferior oblique m. through the frontal-oblique plane, made possible by new SE T1 sequences through the same plane. Position, height, and signal of the m. were estimated. The mean frontal angle formed by the muscle and the sagittal axis measured 29° for the right eye and 27° for the left eye. The muscle was always identifiable in the reformation despite its thin dimensions: 1.9 mm (1.5–2.8) on the right and 2 mm (1.7–2.5) on the left, in low signal silhouetted by the high signal of orbital fat. Thus, thanks to mm by mm reconstructions using FLASH 3D sequence, a good radioanatomic study of the inferior oblique m. by MRI is possible. This could be useful particularly for the strabismus of children.