A Test-Bed for Vision Science Based on Adaptive Optics Scott C. Wilks Charles A. Thompson, Scot S. Olivier, Brian J. Bauman, Lawrence Flath, and Robert Sawvel Adaptive Optics Group Lawrence Livermore National Laboratory and John S. Werner and Thomas Barnes Center for Neuroscience University of California, Davis 95616 This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.

Diffraction-Limited Adaptive Optics and the Limits of Human Visual Acuity normal vision supernormal vision New advances in ophthalmology may enable correction of high-order aberrations in the eye. Advances in laser eye surgery, contact and interocular lenses. Improved aberration correction could provide supernormal vision - better than 20/10 visual acuity, more than a factor of 3 increase in contrast sensitivity. Psycho-physical effects of aberration-free eyesight on visual performance are not known. We are using unique LLNL expertise in adaptive optics to enable detailed scientific studies of the visual performance benefits of improved aberration correction for the general population.

New advances in ophthalmology may enable SUPERNORMAL VISION Normal human visual acuity is 20/20 on the Snellen scale after correction for defocus and astigmatism. The physiology of the average human eye can support better than 20/10 visual acuity if higher-order aberrations are corrected. Psf of 6.8 mm Pupil w/ AO on/off Wavefront of Wavefront of distorted image perfect image Super- normal vision normal vision Imperfect Eye Cornea and Lens New advances in laser refractive surgery and contact lenses may enable correction of high-order aberrations.

Types of aberrations in population 1.4 Mean of 63 eyes 5.7 mm pupil* 1.2 1 Rms wavefront error (µm) 0.8 0.6 0.4 0.2 Z2,0 Z2,-2 Z2,2 Z3,-1 Z3,1 Z3,-3 Z3,3 Z4,0 Z4,2 Z4,-2 Z4,4 Z4,-4 Z5,1 Z5,-1 Z5,3 Z5,-3 Z5,5 Z5,-5 Zernike Modes Defocus Coma Spherical Aberration Astigmatism Regular eyewear Uncorrected high order aberrations: LASIK, custom-made contact lenses *J. Porter, private communication

High-resolution adaptive phoropter combines ophthalmic wavefront sensor with liquid crystal wavefront corrector Conventional Phoropter Wavefront sensor Liquid crystal corrector Ultimately, a clinical ophthalmic adaptive optics system could be used to replace the phoropter in order to allow optometrists to assess high-order aberrations in the eye while the patient directly observes the visual benefit of correction. Permanent correction of high-order aberrations could then be accomplished with custom laser eye surgery or contact lenses.

Aberration-free vision Eye E Diffraction-limited image on retina: resolution only limited by pupil size Eye chart Perfect lens Photoreceptors sample image 1-to-1: optical resolution matches retinal resolution 20/8 “supernormal” vision! Can we really see the “E”?

Adaptive optics control wavefront phase to compensate for optical aberrations corrector Aberrated wavefront Corrected wavefront Wavefront sensor Wavefront control computer

Adaptive optics can provide unique diagnostic capability to study effects of vision correction An adaptive optics system can be used to sense and correct aberrations in a subject’s eye and allow detailed studies of visual performance under a variety of conditions. Deformable Mirror CCD Hartmann-Shack Wavefront Sensor Laser Beacon Optical aberrations in subject’s eye Telescope computer and light source E AB CFDG Eye Chart Adaptive optics is the only demonstrated method for effectively correcting high-order aberrations in the eye

Hamamatsu optically addressed nematic liquid crystal spatial light modulator - operational principles LC LCD ( phase map ( phase intensity LCD Optically written map Optically ( desired phase here) written here) intensity map Spatial Imaging Imaging electrically written here) Backlighting Modulator Light Lens Lens Laser Diode Aberated apprx. 30mw Process Beam C orrected Process Beam Imaging Read Beam Optic Write Beam

Demonstration of high-resolution wavefront control using liquid crystal spatial light modulators High-resolution liquid crystal spatial light modulator Yellow HeNe Laser Collimating Optic Kinematic Mounted Mirror (19 actuator DM or Flat ) T elescope Lens Expanding Telescope Reducing Telescope micro scope Objective 1K x 1K Farfield Scoring Camera Spatial Light Modulator LCD (desired phase map electrically written here) Backlight Diode Write Beam Imaging Lenslet Array 1K x 1K Sensor Kinematicly Mounted (OALCSLM, Flat, or MEMS Device can be installed) 1K x 1K Nearfield Camera Wavefront Reference Source High-resolution wavefront control test-bed schematic HAMAMATSU LC SLM High-resolution wavefront sensor High-resolution wavefront correction results Reconstructed aberrated wavefront Aberrated far-field image: Strehl  0.3 Corrected far-field image: Strehl  0.7 40x50 Hartmann sensor image

SLM stroke vs Voltage shows us where to operate device, to maximize stroke. 450 Hz 500 Hz 550 Hz 600 Hz 650 Hz

The SLM response is slightly uneven over the face of the device. 1 2 3 1 9 5 6 4 7 8 9 We really only care about the PV that gives us the phase we want to wrap at. This means we want to wrap on a Surface, and not just at a pixel value (say 150.)

Plot of the response of the SLM (Stroke) versus grey value (0-256) for our optimal values, 600 Hz, 3.6 Volts.

Wavefront Aberrations of SLM Note: We are currently working with Hamamatsu to improve optical quality of the device.

We write a pattern to the SLM, correcting for the abberations inhernet in the device. Peak to Valley of ~ 400 nm (surface)

Reflected light, for 3 different phase lags. The LC-SLM is perfect for phase wrapping, effectively increasing stroke. Incoming light looks like this for all 3 cases below. l h(x) h(x) l/4 l/2 Reflected light, for 3 different phase lags.

We can apply phase wrapping on the flat file. By wrapping at PV approximately 150, we can take out the 0.7 micron abberation, using only 0.3 microns of stroke!

Phase wrapping the flat file. Either this: both give this flatness of reflecting surface: 0 < PV < 254 or this, written to SLM… 0 < PV < 150 (corresponding to ½ wave Of 630 nm light in WYKO)

Computationally, what does phase wrapping look like? function wrap_phase_new, input ;This function wraps values > 150 ; scale numbers up, so we wrap at 150, not 256 in=input*(256.0/150.0) output = byte(in) output = output*(150.0/256.0) return,output end 300 f(x) 150 300*(256/150) f(x) 150*(256/150) f(x) 256 f(x) 150

Phase wrapping a gaussian. PV = 254 PV = 300 Slice across center 0 < PV < 150 (corresponding to ½ wave Of 630 nm light in WYKO) 0 < PV < 254

Phase wrap the 633 nm, but not the 785nm. Far field spot 633 nm Far field spot Write pattern to SLM Grey bars have Pixel Value = 150 633 light sees “flat” surface, while 785 sees a grating.

Now, phase wrap the 785 nm, but not the 633 nm. Far field spot 633 nm Far field spot Write pattern to SLM White bars have Pixel Value = 254 633 light sees “flat” surface, while 785 sees a grating.

Prototype adaptive phoropter using liquid crystal spatial light modulator

The Rubreye Will be used as a model eye to align, calibrate and perform initial tests on the Adaptive Optics System.

Prototype adaptive phoropter using liquid crystal spatial light modulator

Far field off SLM no aperture, in testbed. reference SLM unpowered SLM with flat file

Control Hardware Integration Effort Dalsa CA-D6 256x256, 8 bit Camera Hamamatsu SLM Adaptive Optics Associates 200mm pitch, 5mm f.l. Lenslet Array Matrox Pulsar Frame Grabber / VGA (SLM) Driver Current Status: All pieces have been procured Dalsa and Pulsar have been successfully run with Dell PC. Software modifications in progress Software Dell PC

Summary: There are many technical challenges in using SLM’s for Vision Correction. Hamamatsu LC SLM We found a voltage-frequency combination that maximizes stroke. Stroke is still limited stroke < 1mm: Solution? Use phase wrapping. SLM has much finer resolution than wavefront sensor – thus, using smaller aperture still gives high resolution, as well as flatter SLM. Chromatic dispersion (different response at different wavelengths) is consistent with advertised values: 2 color solution. Phase Wrapping Principles of phase wrapping shown to work (2 color experiment.) Two color correction (close loop at one color, correct at another) will be our next test.