Abstract Listings 2024

Purpose

To review the literature, both old and new, about numerical aberrations of the extraocular muscles (EOMs) and the levator palpebrae superioris muscle (LPS).

Methods

The authors summarized the embryologic bases and the possible etiopathogenetic causes of numerical aberrations of the EOMs and the LPS. They also propose a classification for these lesions into broad subtypes, and briefly shed some light on the diagnostic challenges, both clinical and radiologic, posed by these anomalies.

Results

Numerical aberrations of EOMs include (1) complete absence of one or more EOMs, (2) the presence of muscle or fibrous bands that connect two EOMs, (3) duplication of an entire EOM, and (4) partial splitting of the muscle (bifid muscles). However, some cases may defy categorization into any of the above and may resemble atavistic remnants of the lower vertebrate retractor bulbi muscle. Broadly speaking, numerical aberrations of the LPS generally fall into the same categories although the LPS has several peculiar numerical anomalies of its own.

Conclusion

Contrary to conventional thinking, numerical variations of the EOMs are not that rare, therefore raising awareness about them is a fundamental clinical keystone not just for the strabismus surgeon but for the orbital surgeon as well. For the orbital surgeon, this may spare the surgeon from pursuing an orbital witch-hunt for these benign innocuous accessory orbital structures that were accidentally discovered by the radiologist and misinterpreted in the report as a lymphoma or a vascular malformation. For the strabismus surgeon, the failure to identify them may result in an unfavorable outcome in strabismus surgery if these structures are not addressed or are missed because of a lack of awareness despite being responsible for generating complex strabismus patterns or having a restrictive potential of their own.

Additional Authors

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