Secondary hyperfunction of unoperated inferior oblique muscle after surgical treatment of strabismus.

Secondary hyperfunction of the inferior oblique muscle IO of one of the eyes is a frequent complication after unilateral recession of the overacting IO of the fellow's eye. It is often observed in cases with bilateral asymmetric hyperfunction of the IO's when these are surgically decreased. The pathogenesis of this secondary hyperfunction is not sufficiently explained yet. We evaluated the condition of unoperated IO in 42 children with unilateral hyperfunction of the IO. In all cases the operation we performed was recession combined with a fixed anteroposition. During the two years follow up period we found no secondary hyperfunction of the unoperated oblique muscle in 31 of the children, mild level of elevation in 7 of them, middle--in 2, and severe in 2 of the children. This observation confirmed our conviction of refraining from simultaneous surgical intervention on both IO muscles when there is hyperfunction of one of them.