Quantitative analysis of structure-function relationship between ocular motility and superior oblique muscle hypoplasia in unilateral superior oblique palsy.

AIMS: To determine the structure-function relationship between the degree of superior oblique (SO) hypoplasia and ocular motility in unilateral SO palsy.

METHODS: A total of 166 patients with unilateral SO palsy were divided into three groups based on their aetiology and high-resolution MRI findings by an in-plane resolution of 0.25 mm: (1) congenital SO palsy and unilateral trochlear nerve agenesis (absent group, n=79), (2) congenital SO palsy and symmetric trochlear nerves on both sides (present group, n=40) and (3) acquired SO palsy (acquired group, n=47) who all had symmetric trochlear nerves on both sides. The degree of SO hypoplasia was defined as the ratio of SO area between the paretic and nonparetic sides (SOP/N ) at the optic nerve-globe junction on MR images. Multivariate analysis was performed to investigate the relationship between SO hypoplasia and ocular motility parameters.

RESULTS: The degree of SO hypoplasia (SOP/N ) showed a weak negative correlation with bilateral head tilt differences in all groups ( β =-0.009, p<0.001 in the absent group; β =-0.003, p=0.034 in the present group; β =-0.007, p=0.002 in the acquired group). There was only a weak positive correlation with SOP/N and hypertropia differences between both gazes in the absent group ( β =0.009, p<0.001) and the acquired group ( β =0.007, p=0.001). In addition, none of the other ocular motility parameters were related to the degree of SO hypoplasia in all groups.

CONCLUSION: Regardless of the aetiology of unilateral SO palsy, the structure-function relationship of the paretic SO size and ocular motility examination was weak and almost negligible.