Loss of fusion and the development of A or V patterns

To test the hypothesis that loss of fusion predisposes the ocular motor system to the development of A or V patterns, we reviewed the pre- and postoperative courses of patients with intermittent exotropia overcorrected with horizontal muscle surgery. Of 332 patients who had surgery, 21 experienced at least 1 month of consecutive esotropia. An equal number of age-matched patients who maintained fusion postoperatively served as controls. No patient in either group had a preoperative A or V pattern. At the first return visit, at least 4 weeks postoperatively, 4 (19%) of the 21 patients with consecutive esotropia showed an A or V pattern, whereas none of the 21 control patients did so. At the end of follow up (mean of 27 months for patients with consecutive esotropia and 29 months for controls), 9 (43%) of the 21 patients with consecutive esotropia showed an A or V pattern versus 1 (5%) of the 21 controls. These findings strongly suggest that loss of fusion is instrumental in the development of A or V patterns, consistent with "sensory torsion" theory of A and V pattern development.