A type of incomitant strabismus characterized by a difference in the horizontal deviation between upgaze and downgaze of at least 10 prism diopters. In A pattern exotropia, the outward deviation is greater in downgaze than in upgaze. In A pattern esotropia, the inward deviation is greater in upgaze than in downgaze. Etiologies may include superior oblique overaction, orbital pulley abnormalities, or ocular torsion.