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    Strabismus much more than orbital pulleys and muscles

    Causes also include connective tissue disorders, nuances of functions of muscle subregions

     

    Many facets of EOMs

    EOMs each have two parts that are independent of one another and do different things. The orbital layer displaces the EOM's pulley posteriorly upon muscle contraction; this layer contains 40% to 50% of the total muscle fibers and inserts on the inside of the pulley.

    In contrast, in the other layer, the global layer, with 50% to 60% of the muscle fiber, the fibers go through the pulley to tendon where they insert on the globe. The orbital layer does not rotate the globe, while the global layer does, Dr. Demer said.

    Recent: VEP, ERG testing brings objective data to clinical practice

    Most of EOMs have two other functional compartments—the horizontal rectus muscles have superior and inferior compartments, and the superior oblique muscle has medial (torsional action) and lateral (mostly vertical action) compartments.

    Surgeries

    Pulleys are now important considerations in eye muscle surgery. Dr. Demer advised that surgical dissection of the intermuscular membranes and tissues around the pulleys should be minimized unless manipulation of pulleys is a specific surgical objective.

    For example, in esotropia that is greater at near than distance, action of the medial rectus muscle can be selectively reduced at near by pulley posterior fixation, suturing the muscle margin to the pulley entrance without scleral suturing at that location.

    However, Dr. Demer noted that in acquired downshift of the lateral rectus pulley due to sagging eye syndrome in older patients, direct pulley surgery is usually not necessary.

    For example, in age-related distance esotropia, he recommends medial rectus recession that is conveniently done under topical anesthesia.

    Dr. Demer also recommends partial tenotomy of vertical rectus muscles for small-angle hypertropia. This technique under topical anesthesia permits reliable correction of hypertropia in the range of 2 to 6 prism D.

     

    More: Click here for ARVO and ASCRS 2016 recaps!

    Joseph L. Demer, MD, PhD

    E: [email protected]

    This article was adapted from Dr. Demer’s presentation at Neuro-Ophthalmology Subspecialty Day at the 2015 meeting of the American Academy of Ophthalmology. Dr. Demer has no financial interest in the subject matter. He reported that some surface coils used were not FDA approved.

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