Comment on – Observation on the curative effect of horizontal rectus transposition combining recess–resect treatment on monocular elevation deficiency with horizontal strabismus

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Dear Editor, We read with great interest the article by Mo et al.[1] on the effectiveness of horizontal rectus transposition combining recess–resect treatment on monocular elevation deficiency (MED) with horizontal strabismus. Although complete transposition of horizontal rectus muscles combined with recess–resect surgery of the paretic eye is well known in the literature, the authors have improvised the surgical technique by accounting for the actual distance between the insertion of the medial and lateral rectus muscle and the limbus and used the limbus as a landmark for the measurement. We would like to bring to notice a retrospective observational study on the effectiveness of surgical procedures in cases of MED, published by us.[2] Our study was conducted in a tertiary eye center in North India on 41 patients diagnosed with MED from June 2015 to January 2017. In our study, six patients had horizontal strabismus along with vertical deviation. Five patients had exotropia and one patient had esotropia. These patients were planned for Knapp’s procedure where the resection of the corresponding horizontal muscle in the affected eye was performed along with transposition to correct the horizontal component of the strabismus. The recession of the horizontal muscle was intentionally avoided if the horizontal deviation was within 30 prism dioptre (PD). We believed that the transposition of a weak (recessed muscle) may weaken the transposition effect, thus diluting the overall effect of Knapp’s procedure. The average preoperative horizontal deviation was 48.3 PD and the vertical deviation was 30.8 PD in our study. The average preoperative horizontal deviation in the present study was 29 PD and the vertical deviation was 28 PD. The average postoperative horizontal deviation in our study was 16 PD and the vertical deviation was 5.6 PD. The mean vertical correction achieved in our study was 25 PD in contrast to the present study where it was 17.5 PD. This, as we believe, could be because of decreased vertical power of a weakened (recessed) muscle. The authors have acknowledged the same in their study “The correction value of the vertical strabismus in the primary eye position of the full transposition of the horizontal rectus combined with the recess–resect was slightly lower than in other similar studies. The new horizontal rectus suture fixation point was different from the standard Knapp surgery, which slightly weakened the effect of Knapp surgery.”[1] Thus, to conclude Knapp’s transposition without recession may be a good option for MED with a horizontal deviation of ≤30 PD, without compromising the vertical correction. However, in larger horizontal deviations, surgeries on the other eye may be needed to correct the residual horizontal deviation. We suggest a tailored approach in patients with monocular elevation deficits to obtain optimal results. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.

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