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Comparative biomechanical analysis of combined treatments for keratoconus

Comparative biomechanical analysis of combined treatments for keratoconus. M. A. del Buey 1 , E. Lanchares 2 , J. A. Cristóbal 1 , B. Calvo 2 , M. Doblaré 2. 1. Department of Ophthalmology “Lozano Blesa” Clinical University Hospital, Zaragoza, Spain. 2.

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Comparative biomechanical analysis of combined treatments for keratoconus

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  1. Comparative biomechanical analysis of combined treatments for keratoconus M. A. del Buey1, E. Lanchares2, J. A. Cristóbal1, B. Calvo2, M. Doblaré2 1 Department of Ophthalmology “Lozano Blesa” Clinical University Hospital, Zaragoza, Spain 2 Aragon Institute of Engineering Research (I3A) University of Zaragoza, Spain The authors have no financial interest in this work. The authors gratefully acknowledge the research support of the Spanish Ministry of Education and Science through the research project DPI2008-02335. 1

  2. INTRODUCTION • KERATOCONUS is a degenerative disorder of the eye in which structural changes within the cornea cause it to thin and change to a more conical shape than its normal gradual curve. • Treatments: - Intrastromal ring segments (ISRS) - Collagen Cross-linking (CXL) - Keratoplasty PURPOSE: To compare the effects of two combined treatments for keratoconus: corneal CXL and ISRS insertion, using a biomechanical model of the keratoconic cornea. 2

  3. Apex Thinnest METHODS Finite Element Model FE model of a healthy cornea (~ spherical) IOP = 15 mmHg FE model of a keratoconic cornea (Thinnest ≈ apex) Cornea Thinnest Surroundings f4mm The pathologic tissue is weaker than the healthy one. The CXL-treated tissue is ~300% stiffer(G. Wollensak & E. Iomdina 2009) 3

  4. METHODS Simulation of CXL, ISCR • ISCR: • O.Z.= 6 mm • length= 160º • t= 0.3 mm • CXL: • UVA: 3 mW/cm2 • Exposure time: 30 min • fbeam 9 mm • Depth: 300 mm 4

  5. RESULTS Clinical results Decrease of the ACD caused by the implantation of ICRS DACD=0.04 5

  6. RESULTS Numerical simulation ICRS insertion Displacement distribution (deformed shape) Stress distribution 6

  7. RESULTS Numerical simulation 1st CXL 2nd ICRS Displacement distribution (deformed shape) Stress distribution 7

  8. RESULTS Numerical simulation 1st ICRS 2nd CXL Displacement distribution (deformed shape) Stress distribution 8

  9. RESULTS Effect of the ICRS insertion The insertion of ICRS causes the applanation of the central area of the cornea (hyperopic effect) and a decrease in the ACD. DACD Close to clinical estimation (after ICRS insertion): DACD=0.04 9

  10. CONCLUSIONS • Our clinical results show that the ACD can be used to quantify the hyperopic effect caused by the insertion of ICRS. • Since the combination of both corneal CXL and ICRS insertion techniques leads to a regularization of the pathological cornea regarding morphology (shape) and biomechanics (tissue behaviour), the sequence of the treatments was analyzed by numerical simulation. 10

  11. CONCLUSIONS • The highest value of stress corresponds to the 1stCXL-2ndICRS treatment. This is due to the increased stiffness of the previously CXL-treated tissue. • The outcomes show a higher effect of the ICRS implantation (↓ACD, ↑s1) when a CXL treatment is previously performed. Thus, biomechanical simulation suggests that ICRS have less effect in advanced keratoconus, due to the weakness of the tissue. madelbuey@telefonica.net 11 María A. del Buey Elena Lanchares

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