Acquired central disruption of fusional amplitude.

Acquired central disruption of fusional amplitude is characterized by a complete loss of fusional amplitude, the patient maintaining fusion for only a moment under test conditions before breaking to constant diplopia. Under normal viewing conditions, the patient has constant diplopia with both eyes open. Patients who have bilateral superior oblique palsy may mimic this loss of fusion and constant diplopia, but they are distinguished by fusing readily on the troposcope, which compensates for the excyclotorsion, in contrast to prisms, which do not remove the double vision. Case reports document an association with convergence palsy, an infranuclear unilateral superior oblique palsy, and a nonparetic acquired strabismus in visual adults. Head trauma is the usual cause.