University of Rochester, Center for Visual Science The Use of a MEMS Mirror for Adaptive Optics in the Human Eye Nathan Doble 1, Geun-Young Yoon 1, Li Chen 1, Paul Bierden 2, Ben Singer 1, Scot Olivier 3 and David Williams 1 1 Center for Visual Science, University of Rochester, Rochester, NY, Boston MicroMachines Corporation, PO Box 15700, Boston, MA, Lawrence Livermore National Laboratory, 700 East Avenue, PO Box 808, Livermore, CA, 94551

University of Rochester, Center for Visual Science Motivation One of the factors that would limit the availability of a commercial, ophthalmic device equipped with adaptive optics is the cost of the wavefront corrector.  A typical ophthalmic instrument ~ $100,000.  The 97 channel Xinetics DM ~ $100,000. The current AO system at the University of Rochester is being used as a testbed for two alternative, low cost technologies, namely a MEMS mirror and an optically addressed LC-SLM.

University of Rochester, Center for Visual Science Overview The possible uses for AO in an ophthalmic instrument The Rochester AO system and testbed Work with an optically addressed LC-SLM Requirements of a MEMS mirror for vision AO The Boston MEMS device Preliminary Results Summary and Future Work

University of Rochester, Center for Visual Science Why do we need AO for vision? A subject could ‘see’ through an AO system to get an impression of the benefits of a vision correction procedure e.g. Lasik or PRK. Perhaps more importantly, an instrument capable of high resolution imaging of the photoreceptor mosaic would allow early detection and better treatment of retinal diseases.

University of Rochester, Center for Visual Science AO could help in …. Nerve fibre layers - Detection of glaucoma, ganglion cell imaging Retinitis Pigmentosa - Photoreceptor loss Age related macular degeneration (AMD) - Two forms: Wet and Dry Better monitoring of various therapies

University of Rochester, Center for Visual Science The Rochester AO System

University of Rochester, Center for Visual Science The Rochester AO Testbed LC-SLM MEMS

University of Rochester, Center for Visual Science System Parameters

University of Rochester, Center for Visual Science The Hamamatsu Optically Addressed LC-SLM Operation With no write light present the impedance of the amorphous Si layer is very high Application of a write light lowers this impedance and the voltage across the LC layer rises in proportion to the light intensity The readout light is then modulated by the movement of the liquid crystal molecules

University of Rochester, Center for Visual Science Operating Parameters

University of Rochester, Center for Visual Science Strehl Ratio vs. LC Pixelation (with defocus and astigmatism)

University of Rochester, Center for Visual Science Advantages/Disadvantages of using the LC-SLM Advantages  High Resolution (480x480 pixels)  Established technology. Commercially available. Disadvantages  Limited corrective range (2 630nm)  Dispersion in the birefringence  Polarization dependant

University of Rochester, Center for Visual Science Dispersion only Phase wrap at 630nm Both wrap and dispersion Broadband Performance (6.8 mm pupil)

University of Rochester, Center for Visual Science Close the AO loop at the WFS wavelength, drive down the residual rms. Perform an open loop correction at the imaging wavelength. Possible solutions Alternatively, do the WFS and the imaging at the same wavelength.

University of Rochester, Center for Visual Science Requirements of a MEMS mirror for Vision AO The important parameters are: i)Stroke ii)Reflectivity iii)Temporal bandwidth iv)Flatness v)Number of actuators hence size of active area vi)Actuator coupling

University of Rochester, Center for Visual Science Wavefront Stroke - 5.7mm Pupil Optimized defocus Optimized defocus and corrected astigmatism (0.25D) Data from Jason Porter, U of R

University of Rochester, Center for Visual Science Wavefront Stroke - 6.8mm Pupil Zeroed defocus Zeroed defocus and astigmatism Data: Hauwei Zhao, U of Indiana70 subjects - left eye shown

University of Rochester, Center for Visual Science Retinal Reflectivity WFS SLD chosen wavelength is ~800nm. Good reflectivity. Short coherence length, minimizes speckle. Shorter depth of retina penetrated. Imaging Wavelength Chosen to be at 550nm, corresponds to the average peak sensitivity of the L and M cone pigment.  Gold >90% (   m  Silver >90% (  m)  Aluminum ~90% (   m

University of Rochester, Center for Visual Science Requirements of a MEMS mirror for vision AO

University of Rochester, Center for Visual Science The Boston MicroMachines MEMS Mirror Photo: Tom Bifano, U of B Electrostatically actuated diaphragm Attachment post Membrane mirror Substrate Actuator

University of Rochester, Center for Visual Science The Mirror and Driver Boards Photo: Paul Bierden, BMC Zygo Interferogram

University of Rochester, Center for Visual Science Comparison of the Mirror Technologies

University of Rochester, Center for Visual Science Initial Results - Static aberration Mirror On

University of Rochester, Center for Visual Science Results for a static aberration mm pupil Before: RMS =  m P-V = 3.34  m SR = 0.03 After: RMS =  m P-V = 1.77  m SR = 0.12

University of Rochester, Center for Visual Science Real Eye results for a 6.8mm pupil Subject: GYY Paralyzed accommodation and dilated Mirror On

University of Rochester, Center for Visual Science Results for a Dynamic Correction mm pupil Before: RMS = 0.74  m P-V = 5.54  m After: RMS = 0.47  m P-V = 4.05  m

University of Rochester, Center for Visual Science Described two types of low cost wavefront correctors Shown the parameters needed of a MEMS mirror for vision AO Described preliminary results for a static and dynamic aberrations which demonstrates the feasibility of using a MEMS mirror Summary  Optimize the current system  Use a metal coated MEMS mirror  Retinal imaging  Possible use of a high stroke (~12  m) piston/tip/tilt MEMS mirror Future Work

University of Rochester, Center for Visual Science Acknowledgements This work has been supported in part 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 and through the National Eye Institute, grants No. 08R1EY04367D and 08P0EY01319F.