Characteristics and course of patients with deteriorated monofixation syndrome

Monofixation syndrome is characterized by small-angle strabismus with vergence fusional amplitudes and "peripheral fusion." Although it is thought to be a relatively stable condition, some patients with this syndrome deteriorate, resulting in an increasing heterotropia, sometimes associated with diplopia. Deteriorated monofixation syndrome is well known among clinicians; however, there are no studies describing the course and outcomes for these patients.

To assess the clinical characteristics, course, and response to therapy of patients with deteriorated monofixation syndrome.

We identified all patients from our database that had an ocular deviation of < or =8 Delta on simultaneous prism cover testing, peripheral fusion, and between 3000 and 67 seconds of stereoacuity (monofixators) who subsequently had an increase in their deviation to >8 Delta, loss of fusion, or diplopia. From this group we assessed patient clinical characteristics, course, and response to therapy.

We identified 29 patients with deteriorated monofixation syndrome who subsequently underwent treatment. Treatment consisted of surgery in 28 patients and minus lens therapy in one patient. Of the study group, 28 (97%) of the patients had a history of esotropia and 20 patients (69%) had a history of amblyopia. Nine patients noted diplopia at the time of deterioration, which persisted in four patients after treatment. In all, 14 patients (48%) met the criteria for monofixation again after therapy, while 20 patients (69%) had successful motor alignment (< or =8 Delta). There was a trend toward poorer outcomes in the diplopic group when compared with the patients who did not have diplopia, although this was not statistically significant (P = 0.26 for regaining monofixation syndrome). Follow-up ranged from 1 month to 21 years.

Though monofixation is considered a stable condition, some patients will deteriorate over time as demonstrated by an increase in the ocular deviation and loss of fusion. In this study 31% of our patients noted the onset of diplopia. Following treatment, 48% of the patients regained monofixation. Patients with diplopia following deterioration of their alignment may be less likely to regain good alignment or monofixation after treatment.