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Raed Aldhafeeri, Patrick Smolinski, Thomas R Friberg; The effect of scleral buckling selection and corneal thinning on axial length of the eye: A biomechanical model.. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):5068.
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© ARVO (1962-2015); The Authors (2016-present)
Lasik procedures result in corneal thinning, as do some corneal disease states. It is well known that circumferential scleral buckles typically result in induced myopia by increasing the axial length of the human eye. This study was done to assess how the application of a scleral buckle of various widths on eyes with decreased corneal thicknesses affects stresses and strains in the tissue, and how it influences the anterior-posterior dimension. A 3-dimensional finite element analysis model was used for this research, and had used a similar model to simulate the effect of surgery on venous occlusions.
A finite element computational model of the eye was developed to assess the changes in stress and strain due to the application of a scleral bundle on an eye with a reduced a corneal thickness. The eye was modelled as an axisymmetric structure with an internal pressure of 2 kPa. The mechanical properties of the tissues were assumed to be linearly elastic with the Young’s modulus and Poisson’s ratio of the sclera, cornea, retina, zonules and lens being (3 MPa, 0.47), (1.5 MPa, 0.42), (0.02 MPa, 0.49), (360 MPa, 0.4) and (6.88 MPa, 0.49), respectively. The maximum thickness of the cornea was taken to be 0.6 mm and the full thickness and a 25% thinning were considered. Buckle widths of 3, 5 and 7 mm were considered with constrictions of 1 and 1.5 mm were applied.
Figure 1 gives the anterior-posterior dimension as of function of the corneal thickness, scleral band width and band constriction.
Increased buckle width, buckle construction and corneal thinning all lead to increased eye anterior-posterior distance and an increase in myopia. Patients who have undergone successful lasik procedures to avoid the need for glasses or contact lenses are more susceptible to this myopic shift than eyes with a normal corneal thickness, independent of buckle width selection. Wider scleral buckles are more likely to induce a greater myopic shift than more narrow buckling elements.
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