Saccadic underaction in concomitant strabismus and Hering′s law : a new neurophysiologic model for binocular motor correspondence

Hering′s law of equal innervation has remained so far as an universal truth with no scientific basis. However, recent reports of Saccadic underactions in concomitant strabismus indicating asymmetric ocular motor innervation is in contradiction to the law. In an effort to understand the inequalities of binocular movements, we propose a neurophysiologic model for both normal and abnormal eye movements. The model hypothesizes that any binocular movement results from the yoking of two monocular reflex loops corresponding to the two eyes, during the plastic stage of development of ocular motor reflexes. The retinal target discrepancy triggers the reflex loop resulting in a monocular corrective movement. As there is a common binocular field, the stimuli to the two eyes are similar causing a similar binocular corrective movement. In abnormal cases coupling of asymmetric motor loops may occur resulting in alternate or unilateral saccadic underactions