AIM: To measure the abnormality of the inferior oblique tendon in patients with congenital superior oblique muscle paralysis.

METHODS: In this cross-sectional, self-control designed study, the tensity of the inferior oblique tendon of both the paralytic and nonparalytic eye were measured during the operations in 30 patients who were diagnosed with exotropia(including intermittent exotropia and constant exotropia )accompanied with single superior oblique muscle paralysis. The tensity of the tendon was measured as the maximal distance of which the inferior oblique tendon could be lifted from the sclera

RESULTS: Inferior oblique had different degrees of thickness, but was tougher and tighter than that of nonparalytic eye. There was a significant difference(P<0.01)in the average tensity of the inferior oblique tendon between the paralytic eyes 6.33±1.35mm and the nonparalytic eyes 7.76±0.81mm.

CONCLUSION: The inferior oblique tendon is stronger and less relaxant in the paralytic eyes.