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

Abstract

To determine the structure-function relationship between the degree of superior oblique (SO) hypoplasia and ocular motility in unilateral SO palsy. 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_P/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. The degree of SO hypoplasia (SO_P/N) showed a weak negative correlation with bilateral head tilt differences in all groups (<i>β</i>=-0.009, p<0.001 in the absent group; <i>β</i>=-0.003, p=0.034 in the present group; <i>β</i>=-0.007, p=0.002 in the acquired group). There was only a weak positive correlation with SO_P/N and hypertropia differences between both gazes in the absent group (<i>β</i>=0.009, p<0.001) and the acquired group (<i>β</i>=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. 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.