[Cyclic strabismus. Presentation of two new cases and critical review of the literature].

Description of cyclic strabismus has been restricted for a long time to circadian esotropia. In this mysterious phenomenon, the eyes are crossed every other day with no binocular vision, but remain perfectly normal during the straight days. The usual characteristics are those of a non-accommodative and non-paretic strabismus, with onset in early childhood. There is no response to conservative treatment, and the cycles become irregular with time until the deviation becomes constant, with an excellent functional result after surgery in every case. Recently, other papers comprising data irrelevant to the classic picture suggest that cyclic strabismus includes, in fact, several different entities. The only common point is the existence of ocular motility disorders that recur more or less regularly, and whose pathologic substrate is primarily heterogeneous, whether it is thought as a mere hypothesis or a likely mechanism. Two new cases of circadian esotropia are presented together with a review of the literature relating to the criteria of the syndrome.