1. Improved Image Quality in AO-OCT through System Characterization
Samelia O. Okpodu
Vision Science and Adanced Retinal Imaging Laboratory, Department of Ophthalmology & Vision Science, University of California, Davis
Mentor: Dr. Julia W. Evans
Faculty Advisor: Dr. John S. Werner
Additional Collaborators: Dr. Robert J. Zawadzki, Steve Jones,
Dr. Scot S. Olivier
Home Institution: Norfolk State University

2. Outline Background Data Importance Proof of Principle AO-OCT vs. OCT
My Research
Installation Process
Data
Proof of Principle
Conclusion &Future Directions

3. Background-What is OCT?
Optical Coherence Tomography (OCT)
In vivo imaging technique
Diagnosis and monitoring treatment of human retinal diseases
OCT permits us to see retinal layers
In Vivo imaging technique that sends out femtosecond infrared pulses and uses optical interference to sense reflections from tissue inhomogenities.
OCT- you can see contrast b/w the layers which is caused by back reflection.
Where the lines appear lighter you’re seeing more back reflection.
OCT B-Scan. UCD

4. OCT vs. AO-OCT
OCT
Allows rapid acquisition of cross sectional retinal images.
Volumetric reconstruction of retinal structures with micrometer axial resolution.
AO-OCT
Improves lateral resolution.
3 microns in all directions.
--AO-OCT scan, AO allows us to have improved lateral resolution
AO-OCT Reconstruction. UCD

5. UCD AO-OCT System
Far-Field CCD
S-H WFS
In an OCT system Calibration errors limit the image quality
A large part of system characterization is understanding calibration error
WFS provides relative measurements of WF error based on calibration
Far Field camera gives us a way to measure calibration independently of the WFS

6. My Research Installing a Far-Field Camera
Proof of principle testing (basic system testing)
Measured errors which affect OCT image quality
Used wavefront measurements to simulate the PSF
Used the far field camera to measure the PSF
Calibration errors: errors that are not seen by the wavefront sensor

7. Installation Process Proper components Optical Constraints
Machine Shop
Optical Constraints
Far Field and WFS both require pupil planes
Mechanical/ Space Constraints
Mechanical/ Space Constraints: Important where installing an instrument in an already existing system.

8. Installation Process Proper space b/w CCD’s, to avoid beam clipping.
Pellicle Beamsplitters
Pupil Plane
Input Fiber
SH WFS
(14x14cm)
Far Field
CCD
Spherical Mirror
Flat Mirror
26 cm
Iris
Pupil Plane
Proper space b/w CCD’s, to avoid beam clipping.
WFS & Far Field Lens require a pupil plane.
Far Field has to be located at the focal length of the lens.
Calibration mode used for proof of principle.
lens
Pupil Plane
Calibration you don’t have a lot

9. Data Types of Data Side by Side comparisons Proof of Principle WFS
Far Field Data
Side by Side comparisons
Proof of Principle
0.12 D neg. Cylinder

10. Proof of Principle: Defocus
Trial Lens: 0.12 D neg. defocus.
Amount of defocus and spot size are directly proportional.
Change in spot size
Measured
Simulated
Measured PSF was what we expected .
Simulated PSF was not what we expected, but we think that is due to limited sampling

11. Proof of Principle: Aberrator
Plastic bag- simulates higher order aberrations
Qualitatively similar
Would prefer quantitatively similar
Improved by correlation or re-sampling

12. Conclusion & Future Directions
Far Field Camera is installed and working in calibration mode.
Far Field data compares relatively well to the WFS data in calibration mode.
Understand Calibration Error
Investigate mitigation techniques to improve the performance of the AO-OCT system.
Far Field Camera Software
Adjust optical design (ghost reflections)
Testing with model & human eye

13. Acknowledgements Dr. John S. Werner, UCD Dr. Julia W. Evans, UCD, LLNL
Dr. Robert J. Zawadzki, UCDMC
Center for Adaptive Optics
Dr. Patricia Mead, NSU
Dr. Demetris Geddis, NSU
Dr. Arlene Maclin, NSU
References:
R. J. Zawadzki et al., “Adaptive Optics- Optical Coherence Tomography: optimizing visualization of microscopic retinal structures in three dimensions,”J Opt. Soc. Am. A /Vol. 24, No. 5 (2007)
J.W. Evans et al., “Characterization of an AO-OCT System,” Proceedings of the 6th International workshop on adaptive optics for Industry and Medicine : University of Galway, Ireland, June 2007.
This work has been supported by the National Science Foundation Science and Technology Center for Adaptive Optics, managed by the University of California at Santa Cruz under cooperative agreement No. AST

14. Light Budget Light throughput is always important
Element
measured power (mW)
Reflectivity/ Transmistivity
predicted power (mW)
coupler
1.2
0.19
1.22
Collimation optics
0.98
1.20
achromatizing lens
1.17
aperture
0.85
1.00
pellicle
0.92 S1
0.87
0.90
Iris
0.78 S2
0.77
Bimorph DM
0.9
0.69 S3
0.67
0.68 S4
0.66
MEMS
0.7
0.46 S5
0.45 S6
0.44
Horiz scanner S7
0.43 S8
0.42
Vert scanner
0.41 S9
0.39
0.40
S10
Flat mirror
Total to Eye
0.36
Light Budget
Light throughput is always important
32% throughput in original system; 29% in current system
Transmitted (%)
Power ratio /Through put (%)
Power ratio before Far Field (%)
Pellicle 1 92 75
Pellicle 2
69.1
Bimorph DM 90
51.9 56
MEMS 70
34.9
37.9
Total input to the eye 29
31.7
Eveloping and error budget is a common tool for improved performance and system design in astronomical AO systems.

15. Extra Images
Aberrator Extras