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Measuring and modeling elasticity distribution in the intraocular lens

Measuring and modeling elasticity distribution in the intraocular lens. Lens System. Zonules. Cornea. Intraocular Lens. Retina. Ciliary Muscle. Lens Anatomy. Lerman S., Radiant energy and the eye, (1980). Helmholtz Accommodation. Coleman’s Theory of Accommodation.

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Measuring and modeling elasticity distribution in the intraocular lens

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  1. Measuring and modeling elasticity distribution in the intraocular lens

  2. Lens System Zonules Cornea Intraocular Lens Retina Ciliary Muscle

  3. Lens Anatomy Lerman S., Radiant energy and the eye, (1980)

  4. Helmholtz Accommodation

  5. Coleman’s Theory of Accommodation Schachar RA, Bax AJMechanism of human accommodation as analyzed by nonlinear finite element analysisANNALS OF OPHTHALMOLOGY 33 (2): 103-112 SUM (2001)

  6. Presbyopia

  7. Presbyopia • Onsets at about 40 years • 100 % prevalence • Complicates Stabismus (cross eyed) • Increases safety risks for pilots

  8. Conceptual Elastic Model Zonules Media Capsule Zonules

  9. Zonules Media Capsule Zonules Lasering Laser

  10. Photodisruption • Femtosecond pulsed laser • Nonlinear absorption • Breakdown only occurs above threshold • Limited to focal spot • No damage to surrounding tissue • Small disruption sites: 1 to 10 mm • Precise location

  11. Acoustic Radiation Force Gas Bubble Acoustic Wavefront Elastic Solid

  12. Advantages • Reflection more efficient than absorption • Bubbles: • Approximate perfect reflectors • High spatial resolution • High contrast for anechoic tissues like lens • Potential in-vivo procedure • Localized measurement

  13. Water Water Water Water Water Gel Gel Gel Gel Gel Porcine Lens Porcine Lens Porcine Lens Porcine Lens Porcine Lens Experimental Set-up Focusing Lens Shutter ND Filter Ultrafast Laser Mirror

  14. Sampling points 1 mm Sampling

  15. Bubble Displacement (Porcine Lens) 40 30 Maximum Displacement (mm) 20 10 0 1 3 5 7 9 Lateral Position (mm)

  16. 40 R2=0.97 Maximum Displacement (mm) 30 20 0.15 0.2 0.25 0.3 (Int. Backscatter) ~ Bubble Radius Bubble Size Dependence Push #1 Push #7

  17. 6 4 Rel. Maximum Displacement 2 0 0 2 4 6 8 10 Lateral Position (mm) Cumulative Normalized Bubble Displacement (N = 12)

  18. 1 0.8 0.6 Relative Stiffness 0.4 0.2 0 1 2 3 4 5 6 7 8 9 Lateral Position (mm) Relative Stiffness – Porcine Lens

  19. Young’s Modulus – Porcine Lens

  20. Conclusions • Acoustic radiation force displaces bubble • Ultrasound tracks bubble • Convert displacement into elasticity • Lens elasticity • Not homogeneous • Function of radial distance

  21. Heys et. al., Experimental Setup Heys KR, Cram SL, Truscott RJW Massive increase in the stiffness of the human lens nucleus with age: the basis for presbyopia? Molecular Vision (2004)

  22. Heys et. al., Results (65 year-old) Heys KR, Cram SL, Truscott RJW Massive increase in the stiffness of the human lens nucleus with age: the basis for presbyopia? Molecular Vision (2004)

  23. Elasticity Distribution vs. Age Heys KR, Cram SL, Truscott RJW Massive increase in the stiffness of the human lens nucleus with age: the basis for presbyopia? Molecular Vision (2004)

  24. Multilayer Model Anterior 2 Light 1 I H G F D E C Polar distance (mm) A B 0 Zonules -1 Capsule -2 Posterior 1 2 3 4 5 6 0 Radial distance (mm)

  25. Caution • Not a direct model of presbyopia • Ignore age-related geometry • Separate biomechanical contributions • Average elasticity • Elasticity distribution

  26. Procedure Displacement Force Original Deformed

  27. Elasticity Distribution (Varying Average Elasticity) Multiplier A B C D E F G H I

  28. Average Elasticity(Varying Average Elasticity)

  29. Accommodation(Varying Average Elasticity)

  30. Elasticity Distribution (Varying Elasticity Distribution) I H G F E D C B A

  31. Average Elasticity(Varying Elasticity Distribution)

  32. Accommodation(Varying Elasticity Distribution)

  33. Lens Biomechanics Polar distance Radial distance

  34. Elasticity Distribution (Example) High Average Favorable Distribution Low Average Unfavorable Distribution

  35. Accommodation (Example) Low Average Unfavorable Distribution High Average Favorable Distribution

  36. Conclusions • Multi-layer model shows accommodation • Two presbyopia mechanisms: • Increased average elasticity (known) • Elasticity distribution change (new) • Elasticity map needed for presbyopia surgery

  37. Colleagues • Tibor Juhasz • Gagik Jotyan • Ron Kurtz • Matthew O’Donnell • Todd Erpelding • Jing Yong Ye • Christine Tse • Marwa Zhody

  38. Biomedical Ultrasound Laboratory Biomedical Engineering Dept. bul.eecs.umich.edu Center for Ultrafast Optical Science www.eecs.umich.edu/CUOS/ University of Michigan IntraLase Corporation, Irvine, CAwww.intralase.com Supported by NIH grant • R21 EY015876

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