Elsevier

Survey of Ophthalmology

Volume 47, Issue 1, January–February 2002, Pages 27-35
Survey of Ophthalmology

Major review
Anomalous Orbital Structures Resulting in Unusual Strabismus

https://doi.org/10.1016/S0039-6257(01)00285-5Get rights and content

Abstract

Anomalous orbital structures are a rare cause of strabismus. These structures attach to the globe and produce a mechanical restriction, resulting in incomitant motility disorders. Three types of anomalous structures have been described. The first arise from the extraocular muscles themselves and insert in abnormal locations. The second are fibrous bands located beneath the rectus muscles. The third are discrete anomalous muscles that originate in the posterior orbit and insert in abnormal locations on the globe. These structures have been associated with unusual patterns of strabismus. Clinical findings that suggest the presence of anomalous orbital structures include globe retraction not associated with Duane retraction syndrome, very large vertical strabismus, and an elevation deficit that is worse in abduction. When looking for anomalous orbital structures in patients with atypical strabismus, imaging studies should be considered.

Section snippets

Historical review

Anomalous orbital structures that attach to the globe and cause restriction of motility have been reported as a rare cause of unusual strabismus during the last century. The earliest cases were discovered at autopsy, and no clinical information regarding motility abnormalities was included. Nussbaum first reported this anomaly in 1893 in a patient with an accessory muscle that arose from the lateral rectus muscle and divided into three heads. One of the heads rejoined the lateral rectus muscle,

Structures arising from the extraocular muscles themselves and inserting in abnormal locations

The first type of anomalous orbital structure is characterized by structures that originate from the rectus muscles and insert in abnormal locations. Apple reported a patient with a congenital abduction deficit who was found to have a 4-mm wide muscular band that inserted posterior to the normal medial rectus muscle insertion and extended posteriorly 1.5 cm, where it fused with the internal surface of the medial rectus muscle.1 He described a second patient with a similar accessory muscle band,

Histopathology of Anomalous Orbital Structures

Histopathologic findings have been reported in two patients with accessory extraocular muscles. In Fleischer's report published in 1907, the accessory structure was found to have fascicles of extraocular muscle.7 Histopathology of the distal portion of the structure in Lueder et al's patient revealed “a paucicellular strip of pale fibrous tissue with small fascicles of mature skeletal muscle at one end. Focally, atrophy and loss of individual muscle fibers were associated with encroachment of

Imaging of Anomalous Orbital Structures

Imaging studies have been reported in only a few patients with anomalous orbital structures. Mühlendyck et al reported CT results in two patients.14 The first patient, who had significant restriction of extraocular movements in all directions, had no abnormalities on her initial CT scan. Repeat studies with a higher resolution scanner later revealed a structure inserting near the supero-medial aspect of the optic nerve. The second patient, who had limited upgaze, had a structure that inserted

Clinical Findings Suggesting Possible Anomalous Orbital Structures

When evaluating patients with incomitant strabismus, one looks initially for motility abnormalities that are characteristic of a specific clinical entity (e.g., an elevation deficiency that is present only in adduction is typical of Brown syndrome). If the pattern of a restrictive strabismus is atypical, the differential diagnosis broadens to include orbital trauma, orbital masses (e.g., tumor), thyroid ophthalmopathy, and intrinsic extraocular muscle abnormalities. The presence of an accessory

Treatment

Not all anomalous orbital structures result in strabismus. Some of these structures appear to have been found in patients incidentally, either at autopsy24 or during surgery for a problem unrelated to the anomalous structure.2, 17 Therefore, it is important to correlate the motility findings with the location of the anomalous orbital structure. If the structure produces a clinical effect, it should be one of restriction, limiting motility in the direction away from the anomalous structure.

The

Conclusion

Anomalous orbital structures are a rare cause of strabismus. They should be considered in patients with atypical restrictive strabismus. Recognition of these structures may be difficult, given their rarity. The presence of specific unusual motility patterns and orbital imaging may assist in diagnosis. Release of the restrictive structures may improve motility in some patients.

Method of Literature Search

MEDLINE and Ovid were used to search the medical literature from 1966 to the present. Other sources included references in identified articles and textbooks. Key words used were extraocular muscles, anomalous, accessory, and retractor bulbi. Four German and one French article were translated.

Outline

I. Background

A. Historical review

B. Embryology of the extraocular muscles

II. Types of anomalous orbital structures

A. Structures arising from extraocular muscles and inserting in abnormal locations

B.

Acknowledgements

The author gratefully acknowledges the assistance of Joern Soltau, MD, and Alex Levin, MD, in translation of original articles. The author has no commercial or proprietary interest in any product or concept discussed in this article.

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