Purpose: To study patients with monofixation and presumed intermittent exotropia with monofixation with the specific intent of determining if they should be categorized as separate diagnostic entity than intermittent exotropes with bifoveal fusion.
Design: A retrospective re-analysis of data from 2 previously published prospective randomized clinical trials on the treatment of intermittent exotropia with attention to the occurrence of the monofixation syndrome.
Methods: A single-center institutional practice study of 215 patients from 2 separate consecutive randomized series undergoing surgery for presumed intermittent exotropia. Outcome measure was the presence of monofixation after surgery.
Results: Of 215 patients undergoing surgery for presumed intermittent exotropia, 194 were over 3 years of age at surgery, had bifoveal fusion, and did not have a preoperative manifest microtropia. None of them developed the monofixation syndrome after surgery. An additional 14 patients who had been previously excluded from those studies because they were too young for sensory testing were included in this study. Seven of them (50%) had the monofixation syndrome after surgery. A different 7 patients who had also been excluded from those prior studies because they had a constant microtropia prior to surgery which would build on alternate cover testing were also included in this study. All 7 had the monofixation syndrome after surgery.
Conclusion: The presence of the monofixation syndrome after surgery for presumed intermittent exotropia most likely reflects the fact that it was present preoperatively. Many of these patients manifest a constant microtropia preoperatively and hence should not be called intermittent exotropes. The term monofixational exotropia is more appropriately descriptive.