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 AJ Mechanism of human accommodation as analyzed by nonlinear finite element analysis  ANNALS OF OPHTHALMOLOGY 33 (2): 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
Capsule
Media
Zonules

9. Lasering
Zonules
Media
Capsule
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. Experimental Set-up Ultrafast Laser Water Gel Water Gel Water Gel
Porcine
Lens
Water
Gel
Porcine
Lens
Water
Gel
Porcine
Lens
Water
Gel
Porcine
Lens
Water
Gel
Porcine
Lens
Shutter
Focusing
Lens
ND Filter
Ultrafast Laser
Mirror

14. Sampling
1 mm
Sampling
points

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

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

17. Cumulative Normalized Bubble Displacement (N = 12)
Lateral Position (mm)
Rel. Maximum Displacement 2 4 6 8 10
Normalized for int. backscatter, mean curve normalized for 5 mm
std. Error of the mean

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

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
Lifetime 4.9x longer in nucleus assuming outer4 = cortex, inner3 = nucleus
Lifetime 8.1x longer in nucleus assuming 4 mm = nucleus, avg(1mm 9mm) = cortex
Stiffness 3.0x in nucleus, assuming nucleus = inner3, cortex = outer4
Stiffness 4.3x in nucleus, assuming nucleus = 5 mm, cortex = 2mm & 8mm

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. Light Multilayer Model Anterior Polar distance (mm) Zonules Capsule2
Light 1 I H G F D E
Polar distance (mm) C A B
Zonules -1
Capsule -2
Posterior 1 2 3 4 5 6
Radial distance (mm)

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

26. Procedure
Deformed
Original
Force
Displacement

27. Optical Power the degree to which a lens converges or diverges light,
equal to the reciprocal of the focal length
ra = anterior radius of curvature
rp = posterior radius of curvature
t = polar lens thickness
n1 = index of refraction for lens
n2 = index of refraction for vitreous

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

29. Average Elasticity (Varying Average Elasticity)

30. Accommodation (Varying Average Elasticity)

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

32. Average Elasticity (Varying Elasticity Distribution)

33. Accommodation (Varying Elasticity Distribution)

34. Lens Biomechanics
Polar distance
Radial distance

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

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

37. Conclusions Multi-layer model shows accommodation
Two presbyopia mechanisms:
Increased average elasticity (known)
Elasticity distribution change (new)
Elasticity map needed for presbyopia surgery
Lifetime 4.9x longer in nucleus assuming outer4 = cortex, inner3 = nucleus
Lifetime 8.1x longer in nucleus assuming 4 mm = nucleus, avg(1mm 9mm) = cortex
Stiffness 3.0x in nucleus, assuming nucleus = inner3, cortex = outer4
Stiffness 4.3x in nucleus, assuming nucleus = 5 mm, cortex = 2mm & 8mm

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

39. Biomedical Ultrasound Laboratory Biomedical Engineering Dept.
bul.eecs.umich.edu
Center for Ultrafast Optical Science
University of Michigan
IntraLase Corporation, Irvine, CA
Supported by NIH grant
R21 EY015876