The paralysis of the fourth cranial nerve (paralysis IV), commonly known as the superior
oblique muscle (SO) paralysis, represents half of vertical strabismus. The diagnosis of SO
paralysis and of its congenital or acquired etiology, are based on a range of clinical
findings. The three main clinical diagnostic elements are the hypertropia in paralyzed side
which increases in adducted position, the positivity of Bielschowsky head tilt test and the
twisting of the eye fundus. These criteria are always considered together and are
interdependent. The diagnostic value and the sensitivity of each of these signs is not
defined. Brain and orbital Magnetic Resonance Imaging (MRI) allowed a better understanding of
the physiopathology of a number of oculomotor disorders.
For this reason, MRI constitute a reference for the SO palsy. The atrophy of the SO muscle is
qualitatively determined by the asymmetry of muscle volume on two contiguous coronal MRI.
The diagnostic value of various clinical signs observed in SO paralysis (sensitivity,
specificity) remains unknown.