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 (SO) 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 (SO) showed a weak negative correlation with bilateral head tilt differences in all groups (=-0.009, p<0.001 in the absent group; =-0.003, p=0.034 in the present group; =-0.007, p=0.002 in the acquired group). There was only a weak positive correlation with SO and hypertropia differences between both gazes in the absent group (=0.009, p<0.001) and the acquired group (=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.