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Raed Aldhafeeri, Patrick Smolinski, Thomas R Friberg; The effect of segmental scleral buckling on corneal astigmatism and axial length of the eye: A biomechanical model. Invest. Ophthalmol. Vis. Sci. 2016;57(12):1032.
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© 2017 Association for Research in Vision and Ophthalmology.
Lasik procedures result in corneal thinning, as do several 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. They also induce astigmatism in the cornea. This study was done to assess how the application of a segmental scleral buckle induces stresses and strains in the tissue, how it influences the anterior-posterior (axial) dimension, and the shape of the cornea. A 3-dimensional finite element analysis model was used for this research, and had used a similar model to simulate the effect of radial optic neurotomy (RON) 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 segmental scleral buckle on an eye. The eye was modelled as an three-dimensional structure with an internal pressure of 2 kPa. The mechanical properties of the tissues were assumed to be linearly elastic with the elastic 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. The buckle width was taken to be 3 mm and 90° and 360° buckles were considered with 0.5 mm constriction.
Table 1 gives the change in the anterior-posterior eye dimension and the diameters of the cornea as a function of segmental buckle angular length. Note for the partial buckle the cornea becomes elliptical with a major and minor axis.
Increased buckle angular length leads to increased eye anterior-posterior distance and an increase in myopia. Segmental buckles introduce an asymmetric distortion of the cornea leading to a difference in major and minor axis radii. Patients who have undergone successful lasik procedures to avoid the need for glasses or contact lenses may be susceptible to this myopic shift and astigmatism with corneal buckling.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
Table 1. Change in eye geometry for different buckle angular lengths.
Figure 1. Deformed model of an eye with 90° buckle.
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