Does Surgical Resection of Horizontal Extraocular Muscles Disrupt Ocular Proprioceptors?

Abstract

Purpose

It has been promoted that disturbance of ocular proprioception may play a role in the pathogenesis of concomitant strabismus and other types of oculomotor anomalies. The aim of the study was to obtain knowledge about how surgical foreshortening of the myotendinous region potentially affects the proprioceptors that resides in this area of the muscles and to test the hypothesis that avoiding disruption of ocular proprioceptors result in a more favorable long term postoperative result.

Patients and Methods

The distal end of the lateral and medial rectus muscles from patients with manifest concomitant strabismus with a deviation of ≥15 prism diopters (PD) were collected during strabismus surgery and processed for light microscopy by standard histochemical techniques. Histological analysis served to differentiate between the tissue samples containing pure tendon, versus samples containing the myotendinous junction. Criteria for successful outcome was defined as a residual angle of deviation less than 10 PD. The binocular status of the patient was measured pre- and post-operatively at 6-months of follow-up.

Results

Tissue samples from 43 patients (median age 19 years old, range 3–58 years) were collected during surgery. Twenty-six of the samples contained pure tendon, while 17 contained muscle fibres. The evolution of the post-operative result revealed a moderate reduction in the residual angle of deviation in patient-samples containing pure tendon. In contrast, the residual angle of deviation clearly increased in patient-samples containing muscle fibres. The difference between the two groups reached statistical significance after 6 months. Successful outcome was found to be more than three times more likely in cases where surgery was performed in pure tendon, compared to muscle fibres.

Conclusion

The current study supports the hypothesis that avoiding disruption of ocular proprioceptors, located in the distal myotendinous region, results in a more favorable postoperative result.

Keywords:

• strabismus
• surgical outcome
• proprioception

Abbreviations

EOM, extraocular muscle; LRM, lateral rectus muscle; MRM, medial rectus muscle; ET, esotropia; XT, exotropia; IMCs, innervated myotendinous cylinders; BSV, binocular single vision; PD, prism diopter; BCVA, best corrected visual acuity; D, diopters; R&R, recession–resection.

Data Sharing Statement

The dataset generated and analyzed in this study is not publicly available yet because it is a part of the PhD work in progress. Data information is available from the corresponding author.

Ethics Approval and Consent to Participate

This study was conducted following the Declaration of Helsinki and was approved by the Ethics Committee of the State University of Medicine and Pharmacy Nicolae Testemitanu (No.36/76 (2016)). Written informed consent was approved by the EC SUMP and obtained before the patients’ participation in the survey and from the parents or guardians for patients under 18 years old.

Patient and Public Involvement Statement

It was not appropriate or possible to involve patients or the public in the design, or conduct, or reporting, or dissemination plans of our research.

Author Contributions

All authors made a significant contribution to the work reported, whether that is in the conception, study design, execution, acquisition of data, analysis and interpretation, or in all these areas; took part in drafting, revising or critically reviewing the article; gave final approval of the version to be published; have agreed on the journal to which the article has been submitted; and agree to be accountable for all aspects of the work.

Disclosure

The authors declare that they have no competing interests.

Additional information

Funding

No funding to declare.