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Mathew Francis, Natasha Pahuja, RUSHAD SHROFF, Rohit Shetty, Kavya Devanapalli, Abhijit Sinha Roy; A novel inverse finite element approach to analyze corneal deformation after SMILE and LASIK. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4317.
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© ARVO (1962-2015); The Authors (2016-present)
Current evidence of biomechanical changes after small incision lenticule extraction(SMILE) and femtosecond laser-assisted in-situ keratomileusis(FS-LASIK) have been inconclusive. This study aims to analyze the acute biomechanical changes associated with SMILE and FS-LASIK using a novel inverse finite element model(I-FEM)
A total of 18 patients were recruited with similar bilateral refraction. The patients underwent SMILE in one eye and FS-LASIK in the other eye. After detailed clinical examination, patients underwent imaging on Pentacam HR and Corvis-ST. These measurements were performed before and after surgery(1, 3 and 6month). The cap/flap depth was set to 110µm. The treatment diameter was 7.8mm and 9mm for SMILE and FS-LASIK, respectively. Corneal tomography from Pentacam-HR was used to construct 3-D corneal model and mesh. The mesh included separate zones for the epithelium, cap/flap and stroma. The I-FEM was based on fiber dependent hyperelastic tissue model considering multilayer corneal structure(Sinha Roy et al, J Mech Behav Biomed Mat, 2015). The I-FEM derived the best fit material properties to describe the corneal deformation measured by Corvis-ST. Using the computed properties, stress strain analogue for each measurement was formulated by simulating intraocular pressure(IOP; 0-60mmHg) acting on posterior surface of the cornea. The displacement of the corneal apex was calculated from stress-strain analogue
Stress-strain analogue of the eyes before and after SMILE(Fig a) and LASIK(Fig b) are shown. At an IOP=30mmHg, displacement of the corneal apex was noted. In LASIK eyes, the displacement increased acutely at 1month followed by continued remodeling(-9.3%) up to 3months(Fig c). However, there was slight recovery of corneal biomechanical strength up to 6month(+12.8%). In SMILE, corneal displacement remained the same at 1 and 3month indicating biomechanical stability. Up to 6month, there was significant recovery such that corneal displacement was less(+27.8%). Similar trends were observed at all other IOPs
There was biomechanical weakening both after SMILE and LASIK. However, SMILE showed more biomechanical stability and improved recovery of biomechanical strength than LASIK. Longitudinal changes obtained from stress-strain analogue could be partly due to change in the hydration level of the tissue. Further, long term data is needed to confirm the findings
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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