Feasibility of using backscattered light to recover refractive
- 1. Feasibility of Using Backscattered Light to Recover Refractive Index Gradient in Biological Samples PAYMAN RAJAI Supervised by Dr. REJEAN MUNGER Visual Optics Lab, The Eye Institute
- 2. The Eye
- 3. The Crystalline Lens • A: single layer of epithelial cells at the anterior surface • E: Cells in the equatorial section • P:The posterior surface has no epithelial cells • IC: Inner Cortex • N: Nucleus • Gradient index along vertical and horizontal axes• Gradient index along vertical and horizontal axes • Circular symmetric in Equatorial plane. Physiology of the Lens, GEORGE DUNCAN and I. MICHAEL WORMSTONE Equatorial Plane
- 4. Stating the Problem • The variation in the gradient is still the challenging question • No direct measurement has been done • All previous techniques detected and analyzed the transmitted light. • All previous studies needed the lens to be in laboratory• All previous studies needed the lens to be in laboratory situation, out of the eye • All previous techniques are valid in equatorial plane
- 5. Foundation of Previous Studies: Ray Tracing Approach •Laser beam •Equatorial plane •circular symmetry Cynthia Wilson Thesis 2010
- 6. The Goals of my Project • Direct measurement of the index profile • Detect and analyze the backscattered light • Utilize the commercially available FD-OCT as a high precision tool to extract depthhigh precision tool to extract depth information
- 7. The Benefits of the Project • Enabling measurement in real situation • Enabling individual measurement, individual eye modelling • Enabling more precise refractive surgery• Enabling more precise refractive surgery • Extendable to other areas
- 8. Optical Coherence Tomography Time Domain OCT Fourier Domain OCT Fercher, Rep. Prog. Phys. 66 (2003) 239–303
- 11. Assumptions in conventional OCT δ-like object’s structure Uniform and homogeneous refractive index for the whole sample Reflectivity of each layer does not depend onReflectivity of each layer does not depend on the refractive index
- 12. Possible Approaches to Solve for Inhomogeneous Refractive Index • Plane Wave Approach• Plane Wave Approach • Diffraction Tomography Approach
- 14. Possible Solutions • Oblique illumination in two different angles: difficult to implement
- 15. Possible Solutions • Oblique illumination in two different angles: difficult to implement • Employing two sources with different spectrums • Simulation based on Matrix method of EM wave propagation
- 18. Born Approximation Using the angular spectrum representation yields Born approximation is valid just for very small objects
- 19. Direct application to the OCT
- 20. Rytov Approximation Rytov approximation is valid for smooth fluctuations in phasesmooth fluctuations in phase
- 21. Direct application to the OCT