Walsh & Hoyt: Congenital

Congenital trochlear nerve palsy accounts for 2967% of trochlear nerve palsies. The etiology is unknown. Aplasia of one trochlear nerve nucleus has been documented as part of a congenital nuclear aplasia syndrome or, together with aplasia of the abducens nerve, in a patient with the oculoauriculovertebral dysplasiahemifacial microsomia syndrome (Goldenhar-Gorlin syndrome). Most isolated trochlear nerve palsies are sporadic, but autosomaldominant transmission occasionally occurs. Usually patients with congenital trochlear nerve palsy are neurologically normal. Some have other neurologic deficits, including cerebral palsy. Many have some degree of facial asymmetry. The patients usually develop large vertical fusion amplitudes and a head tilt, allowing them to avoid diplopia. There may be decompensation after a minor head injury or without any antecedent event. When these patients are evaluated, a review of old photographs, such as a drivers license, may reveal a preexisting head tilt. In addition, direct measurement of vertical fusion amplitudes may establish the diagnosis. Normal persons have a vertical fusion range of only 36 prism diopters, whereas patients with congenital superior oblique paresis may have 1025 prism diopters of vertical fusion amplitude.