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S. Schutte, F. C. T. van der Helm, M. J. C. Eijkemans, J. Polling, H. J. Simonsz; A Model for Reoperations in Strabismus Surgery. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4877.
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© ARVO (1962-2015); The Authors (2016-present)
To make a model of causes of reoperations in strabismus surgery and to determine the number of preventable reoperations by improvements in the trajectory of strabismus surgery.
Congenital esotropia (CE) was used as an example for strabismus surgery. In a historic-cohort study (Ned Tijdschr Genees: 143:2121) we previously established the relationship between the postoperative angle of strabismus and the chance of a reoperation. Sensitivity analysis of the surgical trajectory was used to determine how much each source of variance in the surgical trajectory contributed to variance in the postoperative angle of strabismus.To make the model, data were used from previous studies: (1) We measured accuracy in prism cover tests; six patients were examined by six orthoptists and concordance of the measurements was assessed (the latent angle at distant fixation had a 90% confidence interval of 5 degrees) (2) we determined the error in relocation of the muscle insertion during surgery by systematically analyzing photographs that were taken during surgery (+/-0.5mm) and (3) we used a mechanical model to investigate the influence of anatomical and physiological factors. Subsequently, we could derive the overall reduction in the number of reoperations that can be achieved by, for example, more accurate preoperative measurements, more precise surgery and accounting for anatomical and physiological variation. As a validation, we multiplied the relation between chance on reoperation and preoperative angle of strabismus with the postoperative angles of strabismus we found in the bilateral recession vs. recession-resection study (ARVO, 2002).
The model predicted a reoperation rate of 18%. Literature reports approx. 20% when the child is first operated at the age of four, but higher when the child is first operated at an earlier age. Approx. half of the reoperations are caused by inaccuracy in the measurement of the angle of strabismus and imprecise surgery.
Improvements in strabismus surgery can reduce the reoperation rate which would improve well-being of the patients and possibly reduce the costs. The model can be adopted for application in accommodative esotropia, convergence excess, exotropia, and paralytic strabismus.
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