Inferior rectus aplasia simulating contralateral monocular elevation deficiency.

Inferior rectus agenesis is usually not considered in the differential diagnosis of vertical strabismus because of its rare incidence. The authors examined an infant who presented with monocular elevation deficiency and was finally found to have contralateral inferior rectus agenesis by magnetic resonance imaging. Inferior rectus agenesis could manifest as contralateral elevation deficit. Careful extraocular motility examination and imaging study are essential for the diagnosis of inferior rectus aplasia.