Various forms of cyclic strabismus have been described. A cyclic variation in binocular function modifying a tendency to strabismus is said to be the underlying mechanism. Cyclic esotropia developed in two adult patients, one having no demonstrable binocular function and the other having suffered complete unilateral visual loss in the affected eye. In each case, on the "good days" there was still a manifest esotropia, in contrast to those patients with cyclic esotropia and good binocular function in which the eyes are straight on the "good days." The presence of binocular function is not required for the development of cyclic strabismus, although the level of binocular function is correlated with the ocular alignment on the "good days."