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M.M. Maier, S.M. Bauer, I.M. Lanzl, K.E. Kotliar; How Does Optical Refraction Change in Myopia, Emmetropia and Hypermetropia After Encircling Band Procedure? A Biomechanical Model . Invest. Ophthalmol. Vis. Sci. 2005;46(13):5523.
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Scleral buckling and encircling band are surgical procedures to treat retinal detachment. Especially the encircling band leads to elongation of the optical axis and ensuing changes in refraction. We applied mathematical modeling to describe the effects on globe deformation and refraction after encircling band surgery. Goal of the model is to better predict post surgical refractive outcomes.
A biomechanical model of the process was developed applying principles described by Mironov & Bauer (2002). The numerical simulation was performed for hypermetropic, emmetropic and myopic eyes applying Mathlab 6.1. The difference of scleral thickness, anisotropic scleral rigidity and dimensions of the globe were considered.
Analysing the stress–strain state of the eye shell, the shell deformation consists of several elements, namely the displacement of scleral components according to scleral rigidity, position and force of the encircling band and presence or absence of vitreous. The ensuing deformation defines the change in axial length, corneal curvature and thus refraction. The results for change of refraction relatively to encircling band shortening are represented in the table:
Our model shows relatively small refractive changes. The calculated values are consistent with our clinical experience. It helps to calculate postoperative intraocular pressure and refractive changes. According to our theoretical estimations refractive changes after surgery depend on initial form of the eye, related to the type of refraction. It seems, that the changes in volume during the surgery and biomechanical characteristics of the corneo–scleral shell have more influence on the changes of optical axis and postoperative refraction, than the initial form of the eyeball.
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