Central Disorders of Horizontal Ocular Alignment

This discussion will focus on those acquired disorders of the central neuraxis that commonly cause exotropia or esotropia. A broad discourse on this topic would incorporate those innumerable ailments that produce strabismus by the simple mechanism of nuclear or intranuclear paresis of the lateral or medial recti. However, I will limit my coverage of these more mundane problems and will concentrate on supranuclear disorders of horizontal alignment. Many of these latter conditions may act by creating tonic imbalances within the vergence eye movement system; excessive convergence tone with respect to divergence tone would be expected to cause esotropia, while the converse situation would produce exotropia. Although this general mechanism seems an attractive explanation for many central heterotropias, one must keep in mind that historical descriptors like 'convergence insufficiency' and 'divergence paralysis' tend to imply more than is actually known regarding the pathophysiologic mechanisms of these disorders. Given their pivotal importance, I will begin this chapter with a brief review of the anatomy and physiology of normal disjunctive ocular movements.