Congenital ocular motor apraxia in twins. Findings with magnetic resonance imaging.

A pair of identical twins, whose features met Cogan's classic description of congenital ocular motor apraxia, were examined. Each had an absence of willed horizontal saccades and demonstrated classic head thrusting. Magnetic resonance imaging revealed hypoplasia of the corpus callosum. Fourth ventricle enlargement and generalized cerebral hypoplasia were also present but were more pronounced in the sibling with the more delayed motor development. The significance of these findings is discussed in light of our understanding of the control mechanism of volitional eye movements.