Dose effect of botulinum toxin a in heterotropia and heterophoria

To evaluate the short-term dose effect of botulinum toxin in manifest and intermittent horizontal strabismus types.

Dysport of 2 international units was injected into a single muscle in cases of constant esotropia and exotropia plus decompensating esophoria and exophoria. Electromyography (EMG) signal was recorded during each procedure. Angle of deviation was measured in each case pretreatment and posttreatment at 2 weeks by prism cover test for near and distance fixation. Change in deviation was evaluated by nonparametric statistical evaluation.

Sixty-six patients were reviewed: 30 males and 36 females. The mean age was 24 years (1-79: SD 20.4). Of the 66 patients, 28 had botulinum toxin to the right eye and 38 had it to the left eye. Thirty-nine had eso deviations (19 constant, 20 intermittent) and 27 had exo deviations (12 constant, 15 intermittent). EMG signal was classed as excellent (30%), good (26%), low (6%), or absent (38%). Percentage net change in angle of deviation was 52% to 60% for eso and exo deviations at near and distance fixation. No association was found in extent of reduction of angle of deviation for type of deviation, presence of constant or intermittent deviation, eye injected, or EMG signal.

All changes in angle of deviation were significant. Larger pretreatment angles of deviation did not preclude significant changes in angle of deviation using botulinum toxin and significantly greater change in deviation was seen in pretreatment angles greater than 20PD.