Transcript Slide 1

Assessment of wave propagation in mice
cornea and lens using phase stabilized swept
source optical coherence tomography
Ravi K. Manapuram, Floredes M. Menodiado, Jiasong Li, Salavat R. Aglyamov, Maleeha Mashiatulla, Shang Wang,
Stanislav Emelianov and Kirill V. Larin
SFM 2012
25th September 2012
Why do we should study biomechanical
properties of lens and cornea
Lens
Diagnosis
Presbyopia: Change of corneal curvature
Induces changes in
• stiffness of the lens
• strain distribution
• Young’s Modulus
Cataract
Astigmatism
Glaucoma
Age related effects
Cornea
Diagnosis
Keratoconus: Change of corneal curvature
Induces changes in
• strain distribution
• stiffness
• shear modulus
• Bending
Keratecstasia and progressive post LASIK (PPLK)
Better understanding of lens nucleus and cortex
Outcomes of refractive surgeries such as micro
incisions, corneal transplants, etc.,
Study the accommodation process
Accurate measurements of IOP.
Lens development
Corneal Hysteresis
General methods
induce a stimulus and measure the ocular tissue response
1.
2.
3.
4.
Mechanical stimulus
Ultrasound
Laser pulse
Air puff
1.
2.
3.
4.
5.
6.
7.
DMA
MRI
B-mode Ultrasound
Supersonic shear imaging
Acoustic radiation force
Electro optical systems (ORA)
Optical methods including OCT
require tissue stimulation on the order of mm amplitude
Dynamic Mechanical Analyzer (DMA) : in vivo ?
The Ocular Response Analyzer (ORA) is a commercially available clinical instrument
ORA require a large displacement of the corneal surface
The predictability of this system is still under investigation
Outline
1. General methods to quantify stiffness
1. Induce a stimulus and measure the response (wave
parameters)
2. Phase resolved method for quantifying wave parameters
1. Ex vivo and In vitro results published earlier1,2,3
3. 2D amplitude distribution in mice lens in vitro1,2
4. 2D amplitude distribution in mice lens in vivo5
5. Methods to quantify wave velocity
et al., Laser Phys Lett., 8(2), 164-168 (2011).
et al., Proc. SPIE, 7885,78851V (2011).
3Manapuram et al., Proc. SPIE, 8209,82090S (2012).
4Manapuram et al., Laser Phys., accepted (2012).
5Manapuram et al., Invest. Ophth. Vis. Sci., in preparation (2012).
1Manapuram
2Manapuram
System and experiment setup
Excitation unit and measurement unit
Excitation unit
Manapuram et al., Laser Phys (accepted) 2012
Manapuram et al., Laser Phys Lett., 8(2), 164-168 (2011).
Manapuram et al., Proc. SPIE, 7885,78851V (2011).
Procedure
(a)
3D image of the eye showing the
excitation point and the points where
phases are measured
2D image of the eye showing the
capability of PhS-SSOCT for whole eye
imaging
Manapuram et al., Proc. SPIE, 8209,82090S (2012).
Procedure
Optical pathlength modulation amplitude
Amplitude Mapping can be achieved with surface
distance.
Manapuram et al., Proc. SPIE, 7885,78851V (2011).
Phase response from mice cornea in situ
Phase response at the surface of the cornea (a) younger (1 month) mice (b) older
(9 month) mice; points are the real data whereas the line plot is the smoothened
data(Note that the shift in response has no significance due to the lack of
knowledge of time of pulse.
2D amplitude map mouse cornea in situ
0.2 /mm
0.35 /mm
0.714 /mm
1 month old (attenuation: 93% per mm)
0.5 /mm
9 month old (43% per mm)
This lateral spatial anisotropy is to be expected based upon the non uniform
orientation and distribution of collagen fibrils that has been shown in mice.
Manapuram et al., Proc. SPIE, 8209,82090S (2012).
Manapuram et al., JBOL (2012).
Damping of wave amplitude as a
function of age (mice cornea in situ )
(a) Damping of normalized amplitude damping over the distance from the tapping
point and (b) Mean attenuation versus mice age.
Delay in wave (mice cornea in situ )
The harmonic oscillations took 0.2 ms to travel from top surface to the bottom surface
Results of similar studies on mice lens
in vitro
Experiment setup for studies on mice
eye (both cornea and lens) in vivo
Wave quantifying procedure
2D Amplitude map (Lens in vivo)
Top layer
Bottom layer
2D Amplitude map (Cornea in vivo)
Top layer
Bottom layer
Wave velocity quantification on gelatin
phantoms
Conclusions
•
We have extended our previously demonstrated method of quantifying
nanometer-level vibrations to measure mechanical wave propagation in the
mouse lens and cornea in vivo.
•
The method utilizes phase response of the tissue surface to a pulsed excitation and
the phase response is detected using M-mode imaging capabilities of PhS-SSOCT.
•
We have shown that mechanical wave propagation in the cornea of different aged
mice vary significantly, which we attribute to differences in stiffness.
•
Therefore, PhS-SSOCT could be an effective tool for measurements of mechanical
wave propagation in soft tissues.
Acknowledgments