The authors undertook a retrospective study to evaluate the extent of reduced deviation after Botulinum toxin (BT) when used as a postoperative diplopia test. They evaluated effect in 39 patients: 32 exotropia and seven esotropia. The same BT dose was used for all – five units in 0.1ml saline. The median preoperative angle was 40PD (16-78) at near and 40PD (12-77) for distance. The preoperative assessment for follow-up surgery was at a mean of seven months (4-16) after BT injection. Reduced angle of deviation of 15PD or more at either near or distance fixation was noted in 36% of patients. This altered the planned surgery for four cases with a change from 3-muscle to 2-muscle surgery. Reduction was more common for exotropia than esotropia.