Primary inferior oblique overaction in congenital esotropia, accommodative esotropia, and intermittent exotropia.

A statistical analysis of the onset and natural history of primary inferior oblique eye muscle overaction (IOOA) was conducted using the records of 456 strabismus patients. With 5 years or more of follow-up, IOOA developed in 72% of congenital esotropes (CETs), 34% of accommodative esotropes (AETs), and 32% of intermittent exotropes (X[T]s) at an average age of 3.6, 5.2, and 5.2 years, respectively. Incidence of IOOA was positively related to the number of horizontal surgeries in CETs but not in AETs or X(T)s. Incidence was not related to age of onset of strabismus, time from onset of strabismus to surgery, age at first surgery, or decompensation of ocular alignment. Mild IOOA did revert to normal in 12 patients after only horizontal surgery. The association of IOOA with dissociated vertical deviation, as well as symmetry, range of age of detection, and recurrence after surgery are also explored.