Original Article
The Effect of Horizontal Rectus Muscle Surgery on Distance-Near Incomitance

https://doi.org/10.1016/j.ajo.2019.11.016Get rights and content

Highlights

  • •

    Traditional teaching suggests that medial rectus muscle surgery induces more effect on ocular alignment at near fixation, and lateral rectus muscle surgery induces more effect on ocular alignment at distance fixation.

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    Our study shows that neither medial rectus or lateral rectus muscle surgery induces a clinically significant change in distance-near incomitance.

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    Analysis of the small, clinically insignificant change in distance-near incomitance shows that medial rectus muscle surgery is not more likely to achieve more effect on ocular alignment at near fixation, and lateral rectus muscle surgery is not more likely to achieve more effect on ocular alignment at distance fixation.

  • •

    It is not necessary to consider distance-near incomitance when choosing between medial rectus and lateral rectus muscle surgery.

Purpose

To determine the effect of horizontal rectus muscle surgery on distance-near incomitance.

Design

Prospective, comparative, interventional case series.

Methods

Prospective evaluation of patients >7 years old who had medial or lateral rectus muscle surgery at the University of Arkansas Medical Center or Arkansas Children's Hospital between December 2009 and January 2012. Prism and alternate cover testing was performed at distance (6 m) and near (0.3 m) fixation after >1 hour of monocular occlusion at preoperative and postoperative examinations within 1 week, and closest to 1 year after surgery. The change in distance-near incomitance was calculated. Patients with extraocular muscle fibrosis or paralysis were excluded.

Results

Forty-five patients met inclusion criteria. Twenty-five patients had medial rectus muscle surgery, and 20 patients had lateral rectus muscle surgery. Postoperative examinations showed a change in distance-near incomitance ≤10 prism diopters (PD) in 42 of 44 patients evaluated within 1 week after surgery and in all 28 patients evaluated 6-24 months after surgery. Horizontal rectus muscle surgery did not induce a clinically significant change in distance-near incomitance (±2 PD equivalence, TOST confidence interval, −1.8 +1.6 PD, P value = 0.014). Contrary to traditional teaching, medial rectus muscle surgery was not more likely to induce a greater effect at near fixation (P = 0.80) and lateral rectus muscle surgery was not more likely to induce a greater effect at distance fixation (P > 0.99).

Conclusion

Horizontal rectus muscle surgery does not induce a clinically significant effect on distance-near incomitance. Contrary to traditional teaching, medial rectus muscle surgery does not induce a greater effect on ocular alignment at near fixation and lateral rectus muscle surgery does not induce a greater effect on ocular alignment at distance fixation. It is not necessary to consider distance-near incomitance when choosing between medial rectus and lateral rectus muscle surgery.

Section snippets

Methods

This study was prospectively approved by the institutional review board of the University of Arkansas for Medical Sciences and conformed to the requirements of the United States Health Insurance Portability and Privacy Act. Informed consent was obtained from each patient after it was determined that they met the inclusion criteria and were therefore eligible for the study.

We prospectively evaluated all patients older than 7 years who had medial or lateral rectus muscle surgery at the University

Statistical Analysis

Two 1-sided t tests (TOST) were performed to test for equivalence between preoperative and various postoperative incomitance measures. A change of less than ±2 prism diopters (PD) was used to define the region of equivalence. We chose 2 PD as this is the degree of precision to which prism and alternate cover testing can quantify a deviation. In addition, clinicians would agree that a change of 2 PD in a horizontal strabismus is clinically insignificant. An α level of 0.025 was used to determine

Results

A total of 45 patients met inclusion criteria with an age range of 9-87 years, including 7 patients who were younger than 18 years. Prior to surgery, 33 patients had high-grade fusion (≥50 arc on Titmus test), 10 patients had monofixation with low grade fusion, and 2 patients had no fusion. Twenty-five patients had medial rectus muscle surgery, including 21 patients who had medial rectus muscle recessions (dose range 3.5-6.5 mm) for esotropia and 4 patients who had medial rectus muscle

Discussion

Our study prospectively obtained pre- and postoperative measurements after patching for 1 hour to eliminate the effect of fusion and isolate the mechanical effect of surgery. The results show that horizontal rectus muscle surgery does not induce a clinically significant change in distance-near incomitance. In addition, medial rectus muscle surgery does not have a preferential effect on ocular alignment at near fixation, and lateral rectus muscle surgery does not have a preferential effect on

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