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Mechanical Simulation of Corneal Ring Implant Surgery for Keratoconus Treatment Considering Tissue Collagen Structure

Naderi Eshkaftaki, Mohammad Reza | 2020

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 53349 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Asghari, Mohsen
  7. Abstract:
  8. Keratoconus is one of the most common optical (visual, eye) diseases that usually occurs in youth or early third decade of life. In this disease, cornea gets thin and loses it initial shape and becomes conical. Doctors use different methods for its treatment including use of glasses, contact lenses (hard or soft), cornea transplantation and also cross linking of cornea. Each of these methods have their limitations, on the other hand, considering that this disease progresses and intensifies, ophthalmologists use corneal ring implant surgery for the treatment of this disease in its advanced levels. A good ring implant in corneal causes increased strength and also cause corneal to get back to its initial form. On the other hand, since ophthalmologists do not have sufficient information geometry of an appropriate ring for each patient suffering from keratoconus and they only use their experiences, therefore by simulation ring implant inside cornea, useful information could be obtained for ophthalmologists.
    In this thesis, treatment of patient suffering from keratoconus have been studied and efforts have been made in order to exactly simulate ring implant inside cornea by introducing an exact cornea model. In this research, initially lots of simulations have been performed by which optimal height of the ring was obtained. Then, simulation of 9 ring implants was performed with different geometries inside corneal model which has a relatively exact material and similar to a real cornea, also its properties were implemented using UMAT programming in ABAQUS software. For simulations, cornea data have been received from ophthalmologists then using CAD and FEM software, simulation of corneal and its inner ring implant has been performed. Finally using genetic algorithm, Zernike coefficients of out surface of cornea were calculated and using them vision parameters of Cyl and Sph power are obtained and by selecting the most appropriate ring geometry for the patient, it is found that this parameters have improved by 1.25 and 0.6, respectively, compared to the results after the ophthalmologist surgery
  9. Keywords:
  10. Zernike Coefficients ; Keratocanic Corneas ; User Defined Materials (UMAT) ; Genetic Algorithm ; ABAQUS Software ; Ring Implantation

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