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Sander Schutte, Frans C. van der Helm, Huibert J. Simonsz; Impediments in improving Strabismus Surgery. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6371.
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Although the limited accuracy in recession and resection surgery is responsible for approx. 20% of the reoperations (Graefes 2009;247:399-409), the surgical procedure has changed little since 1905. In this study we have analyzed the conditions that impede the development of new surgical devices and procedures for strabismus surgery.
After defining the requirements for accurate strabismus surgery, we studied how current surgical procedures and alternative solutions described in patents meet these requirements. Surgical (higher accuracy, lower risk on adverse events), geometrical (working space limited by nose and orbital rim), legal (e.g. CE and FDA approval) and financial requirements (cost-effectiveness) were considered. To assess the current procedure, we subdivided the surgical workflow into tasks: (1) determining a reference position on the eye and on the muscle (2) holding the muscle and the eye (3) cutting the muscle (4) moving the muscle to its destination position and (5) fixating the muscle. The error sources were identified for each step. To assess the inaccuracies and bottlenecks in alternative solutions we performed exploratory tests.
The first main error source within strabismus surgery is inaccurate determination of reference locations when measuring the target location of the muscle. Variability originates from ambiguous reference locations and re-assessing marked locations. The second error source is inaccurate fixation of the muscle. Variability occurs in entering the sclera with the needle, in locating the knots on the muscle tendon, in tightening the knots and sagging of the muscle between the attachment points. Several solutions have been proposed to overcome these errors, e.g., using more accurate calipers to measure, using adhesives (‘creep’ of the muscle, contamination danger, incomplete resorption) or biodegradable clamps (several patents have been filed, but none have become commercially available) that fixate the tendon over its whole width. Although several solutions exist that could reduce the independent errors, an integral approach has never been made. The main impeding condition is the mechanical complexity of the combined solution: new solutions add considerable complexity to the instrumentation and the procedure, whereas the current procedure is simple and straightforward.
To increase accuracy in strabismus surgery, an integral approach to new instrumentation is required. To compete with the current surgical method, accuracy should be improved without increasing complexity.
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