Consecutive exotropia: does one size fit all?

Consecutive exotropia, the presence of a divergent strabismus where there was previously a convergent strabismus, is most commonly noticed as an iatrogenic occurrence1 which may be immediate or late onset post surgery for an esotropia or, rarely, postbotulinum toxin for an esotropia. In this month’s journal, Chatzistefanou et al (see page 742) report on their experience of reversal of unilateral medial rectus recession and lateral rectus resection for the correction of consecutive exotropia.2 This approach is not new3 4 but the authors demonstrate very well a dose–effect relationship, whereby larger preoperative angles result in a greater prism dioptre reduction per millimetre of surgery undertaken, to some extent, confirming the “uniform surgery” theory for strabismus surgery, that is, the same surgical numbers but different effect depending on the preoperative angle. Their dose–effect relationship is similar to that reported previously5 for this procedure. They chose less than 10 pd from orthophoria as a criterion for success. Is this a reasonable criterion to use? Larson et al 6 showed that cosmetically the threshold for detection of an esotropia, exotropia …