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Ashley S Ko, Roy A Cline; Retrieval of Slipped Muscles: Strategies and Impact.. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):565.
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Slipped extraocular muscle (SEM) is an important and serious complication of a strabismus surgery that is underdiagnosed, often leading to intolerable symptoms and inappropriate reoperations by misguided surgeons. Incidence and management data of SEM is rare. While reference tables with projected corrective change per millimeter of extraocular muscles correction with no previous surgery is readily available, no such reference tables are available for SEMs. Additional data providing specific guidelines for SEM surgeries will make a strong impact on surgical planning and outcome. The purpose of this study was to formulate a nomogram for SEM strabismus surgery, rendering an effective reference and strategy.
This retrospective chart review (13 years, January 2000 - April 2013) is a single centre study approved by University of British Columbia Research Ethics Board. We looked at the type of strabismus and the initial type of surgery performed. The orthoptics data pre- and post- SEM correction surgery was analyzed. We also gathered intraoperative data showing the position of the SEMs and the amount corrected. The primary analysis involved determination of how much correction of alignment was achieved (in prism diopters [PD]) per millimetre of the eye muscle corrected. Other data included gender, age at the time of initial surgery, visual acuity, timing of SEM at presentation (recent <6 weeks; distant >6 weeks), and pathology results.
Total of 70 patient [26 (37.1%) male, 44 (62.9%) female] were included in the study. Twelve (17.1%) cases were recent (<6 weeks) and 58 (82.8%) cases were distant (>6 weeks) events. Pseudotendon was identified clinically and/or pathologically in 67 (95.7%) cases. Effect of muscle advancement for slipped muscles ranged between 0.6 and 9.1 PD/mm. The average effect was 3.92 PD/mm. The median effect was 3.76 PD/mm.
The effect of SEM advancement can be very powerful but also unpredictable and variable. Other factors to consider in assessing each patient and performing the surgery are the quality of muscle and the tightness of the antagonists. It is also likely that sensory suppression and fusion play a major role in the outcome, particularly in the secondary strabismic patients. It is important to remember management and outcome of SEM surgery are multifactorial and surgeons must be aware of the variabilities for each case.
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