comparative biomechanical analysis of combined treatments for keratoconus
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
Comparative biomechanical analysis of combined
treatments for keratoconus
M. A. del Buey1, E. Lanchares2, J. A. Cristóbal1, B. Calvo2, M. Doblaré2
Aragon Institute of Engineering Research (I3A)
University of Zaragoza, Spain
Department of Ophthalmology
“Lozano Blesa” Clinical University Hospital, 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.
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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
INTRODUCTION
To compare the effects of two combined treatments for
keratoconus: corneal CXL and ISRS insertion, using a
biomechanical model of the keratoconic cornea.
PURPOSE:
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METHODS Finite Element Model
FE model of a healthy cornea (~ spherical)
FE model of a keratoconic cornea (Thinnest ≈ apex)
Apex
Thinnest
IOP = 15 mmHg
Surroundings
4mm
Cornea
Thinnest
The pathologic tissue is weaker than the healthy one. The CXL-treated tissue is ~300% stiffer (G. Wollensak & E. Iomdina 2009)
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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
• beam 9 mm
•Depth: 300 m
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Mean values PREOP POSTOP p
ACD 3.38 ±0.30 3.34 ±0.33 < 0.05
K 48.85 ± 4.68 46.43 ± 4.17 < 0.05
Sim K 5.95 ± 2.60 3.66 ± 2.20 < 0.05
Clinical resultsDecrease of the ACD caused by the
implantation of ICRS
RESULTS
ACD=0.04
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RESULTS
Numerical simulation
ICRS insertion
Stress distribution
Displacement distribution (deformed shape)
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Stress distribution
Displacement distribution (deformed shape)
1st CXL
2nd ICRS
RESULTS
Numerical simulation
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Stress distribution Displacement distribution (deformed shape)
RESULTSNumerical simulation
1st ICRS
2nd CXL
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RESULTSEffect 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.
Num.Sim. ICR1st CXL
2nd ICRS1st ICRS2nd CXL
Stress(1)
0.1501 MPa 2 MPa 0.03 MPa
ACD -0.056 mm -0.237 mm -0.045 mm
Close to clinical estimation (after ICRS insertion): ACD=0.04
ACD
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CONCLUSIONS
1. Our clinical results show that the ACD can be used to quantify the
hyperopic effect caused by the insertion of ICRS.
2. 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.
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CONCLUSIONS
3. The highest value of stress corresponds to the 1stCXL-2ndICRS
treatment. This is due to the increased stiffness of the previously
CXL-treated tissue.
4. The outcomes show a higher effect of the ICRS implantation
(↓ACD, ↑1) 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.
María A. del Buey Elena Lanchares
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